Patent Application
20230082796
This application claims priority to and the benefit of Korean Patent Application No. 10-2021-0116497, filed on Sep. 1, 2021, in the Korean Intellectual Property Office, the entire contents of which are hereby incorporated by reference.
One or more embodiments of the present disclosure relate to a cathode active material for a lithium secondary battery, a method of preparing the same, and a lithium secondary battery including a cathode including the same.
As portable electronic devices and communication devices are advanced, there is a great need to develop lithium secondary batteries having high energy density. However, safety of a lithium secondary battery having high energy density may be reduced, and thus improvement in this regard is needed.
In order to manufacture a lithium secondary battery having a long lifespan and reduced gas, studies have been carried out on the use of a single-crystal cathode active material as a cathode active material for a lithium secondary battery.
However, when a single-crystal cathode active material is prepared, a flux is generally used. When a flux is used, it is necessary to go through a washing process, which is an essential process to remove residual salt. Accordingly, manufacturing costs are increased and preparing processes are complicated. In addition, due to heat treatment at high temperature for single-crystallization, single-crystal cathode active materials may have particle agglomeration or productivity thereof may be reduced.
One or more embodiments of the present disclosure include a cathode active material for a lithium secondary battery, the cathode active material having suppressed or reduced aggregation between particles and excellent structural and morphological stability.
One or more embodiments include a method of preparing the cathode active material.
One or more embodiments include a lithium secondary battery which has improved cycle characteristics due to the inclusion of a cathode including the cathode active material.
Additional aspects of embodiments will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments of the disclosure.
According to one or more embodiments, a cathode active material for a lithium secondary battery includes
a nickel-based lithium metal oxide containing single-crystal particles, wherein
a particle size of the single-crystal particles is about 1 μm to about 8 μm, and
a particle size distribution of the cathode active material expressed as (D90-D10)/D50 is 1.4 or less.
According to one or more embodiments, a method of preparing a cathode active material for a lithium secondary battery includes: obtaining a nickel-based metal precursor having pores therein by a co-precipitation reaction of a nickel precursor and at least one compound selected from the group consisting of an M1 precursor and an M2 precursor, and then drying the resulting product;
obtaining a mixture of the nickel-based metal precursor having pores therein and a lithium precursor;
performing a first heat treatment of the mixture to obtain porous oxide particles; and
pulverizing the porous oxide particles, wherein
the M1 precursor may be at least one compound selected from a cobalt precursor, a manganese precursor, and an aluminum precursor, and
the M2 precursor may be a precursor including at least one element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), and zirconium (Zr).
According to one or more embodiments, a lithium secondary battery includes: a cathode containing the cathode active material; an anode; and an electrolyte therebetween.
The above and other aspects and features of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:
Reference will now be made in more detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects of embodiments of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.
Hereinafter, a cathode active material for a lithium secondary battery according to an embodiment, a method of preparing the same, and a lithium secondary battery including a cathode including the same will be described in more detail.
In order to manufacture a lithium secondary battery with improved lifespan characteristics, a cathode containing a single-crystal cathode active material is used.
The single-crystal cathode active material has fewer grain boundaries than the polycrystalline cathode active material (or the single-crystal cathode active material has no grain boundaries), so that due to a limited reaction area between the cathode active material and an electrolyte, a negative surface reaction such as formation of a rock salt phase or a side reaction of the cathode active material and the electrolyte can be suppressed or reduced. Therefore, single-crystal cathode active materials may better withstand mechanical stress due to structural change during charge/discharge cycle, compared to polycrystalline cathode active materials.
It is common to use a flux such as NaCl, KCl, or Na2SO4 when manufacturing a single-crystal cathode active material. However, in the case of using such a flux, it is necessary to go through a washing process which is needed to remove residual salt, resulting in increased preparing costs and a more complicated preparing process. These are obstacles to mass production.
Accordingly, the inventors of the subject matter of the present disclosure developed a method of preparing a single-crystal cathode active material having high crystallinity without using a flux, and a cathode active material obtained using this method. Such a cathode active material has improved structural and morphological stability, and can be mass-produced. In addition, when a cathode containing such a cathode active material is used, safety is improved, and a lithium secondary battery having improved capacity and charge/discharge efficiency can be manufactured.
The cathode active material for a lithium secondary battery according to an embodiment is a nickel-based lithium metal oxide including single-crystal particles, and the particle size of the single-crystal particles may be about 1 μm to about 8 μm, and the particle size distribution thereof represented by (D90-D10)/D50 may be 1.4 or less.
The single-crystal particles used herein refer to i) a one body particle having a primary particle size of 1 μm to 8 μm, ii) an aggregate of primary particles, or iii) a mixture of a one body particle having a primary particle size of 1 μm to 8 μm and an aggregate of primary particles. In this regard, a particle size of the aggregate of primary particles may be from about 1 μm to about 8 μm, and the number of primary particles in the aggregate of primary particles may be 10 or less, for example.
As used herein, the term “one body particle” refers to a structure in which particles are present as independent phases in which particles do not have the morphology of being aggregated with each other.
The cathode active material according to an embodiment may further include an aggregate of 10 or less primary particles.
The particle size distribution may be, for example, about 1.0 to about 1.4 or from about 1.1 to about 1.3.
D90 may be about 4 μm to about 7 μm, and D10 may be about 1.2 μm to about 2.0 μm. D50 may be about 2 μm to about 4 μm. When D90, D10, and D50 of the cathode active material are outside these ranges, dispersibility may be reduced due to aggregation of the cathode active materials, and the specific surface area may be reduced, thereby reducing activity.
In the present disclosure, when the particles are spherical, “size” or “particle size” indicates the average particle diameter, and when the particles are non-spherical, “size” or “particle size” indicates the longer length (e.g., the longest axis of the particle), for example, the average longer length of the particle. The particle size of the particles can be measured using a scanning electron microscope (SEM) or a particle size analyzer. As the particle size analyzer, for example, a HORIBA, LA-950 laser particle size analyzer may be used. When the particle size is measured using a particle size analyzer, the average particle diameter may be D50. D50 refers to the average diameter of particles when the cumulative percentage reaches 50% by volume in the particle size distribution, and refers to the value of the particle size corresponding to 50% from the smallest particle in the distribution curve accumulated in the order of the smallest particle size to the largest particle size, wherein the total number of particles is 100%.
The average particle diameter of the cathode active material may be measured using for example, a laser diffraction method, and in more detail, after the cathode active material is dispersed in a solution, the resultant solution is introduced into a commercially available laser diffraction particle size measuring device (for example Microtrac MT 3000) and ultrasonic waves of about 28 kHz are irradiated thereto with an output of 60 W. In this regard, the average particle diameter (D50) when the cumulative percentage reaches 50% of the particle size distribution obtained by the measuring device, may be calculated.
The term “D10,” as used herein, refers to the average diameter of particles when the cumulative percentage reaches 10% by volume in the particle size distribution, and the term “D90,” as used herein, refers to the average diameter of particles when the cumulative percentage reaches 90% by volume in the particle size distribution.
The particle size of single-crystal particles in the cathode active material according to an embodiment may be, for example, 2 μm to 6 μm, 2 μm to 4 μm, or 2.5 μm to 3.5 μm. When the particle size of the single-crystal particles of the cathode active material is within these ranges, a cathode active material having excellent capacity characteristics may be obtained. In the present disclosure, the particle size may be measured using SEM, BET, and/or the like.
The nickel-based lithium metal oxide may be a compound represented by Formula 1.
Lia(Ni1−x−yM1xM2y)O2±α1 Formula 1
wherein, in Formula 1, M1 may be at least one element selected from Co, Mn, and Al,
M2 may be at least one element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), and zirconium (Zr), and
0.95≤a≤1.1, 0.6≤(1−x−y)<1, 0≤x≤0.4, 0≤y<0.4, and 0≤α1≤0.1, and a case where both x and y are 0, is excluded.
The nickel-based lithium metal oxide may be, for example, a compound represented by Formula 2.
Lia(Ni1−x−y−zCoxM3yM4z)O2±α1 Formula 2
wherein, in Formula 2, M3 may be at least one element selected from Mn and Al,
M4 may be at least one element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), and zirconium (Zr), and
0.95≤a≤1.1, 0.6≤(1−x−y−z)<1, 0≤x<0.4, 0≤y<0.4, 0z≤<0.4, 0≤α1≤0.1, and a case where x, y, and z are each 0, is excluded.
The expression “a case where x, y, and z are each 0” represents “a case where x, y, and z are all 0”.
The amount of nickel in Formula 2 may be, for example, about 60 mol % to about 95 mol %, or about 80 mol % to about 95 mol % (based on the total amount of metals other than lithium).
The peak intensity ratio I(003)/I(104) measured by X-ray diffraction analysis of the cathode active material for a lithium secondary battery according to an embodiment may be about 1.2 to about 4.0, or about 1.2 to about 2.0.
In X-ray diffraction analysis, the peak intensities 1(003) and 1(104) refer to the peak intensity of the (003) plane and the peak intensity of the (104) plane, respectively. In addition, the peak intensity ratio I(003)/I(104) may be a ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane, and is a parameter made to evaluate the degree of uniform orientation of the crystal grains. From I(003)/I(104), the degree of cation mixing or cation exchange may be evaluated.
The (104) plane is a plane perpendicular (e.g., substantially perpendicular) to the surface of the lithium ion movement path, and as the degree of orientation of the crystal plane of the layered structure is increased, the peak intensity of the (104) plane is decreased. Accordingly, as the degree of orientation is increased, the peak intensity of the (104) plane is decreased and I(003)/I(104) is increased. As the peak intensity ratio I(003)/I(104) increases, the stability of the structure of the cathode active material structure is improved.
In the case of the cathode active material of the present disclosure, W(003) may be about 0.110 to about 0.130, for example, 0.117, and W(104) may be about 0.095 to about 0.145, for example, 0.102. In addition, W(003)/W(104) obtained by X-ray diffraction analysis of the cathode active material is about 1.01 to about 1.09, about 1.03 to about 1.09, or about 1.03 to about 1.08. For example, it can be seen that crystallinity is improved. In this regard, W(003) represents the full width at half maximum (FWHM) of the peak corresponding to the (003) plane, and W(104) represents the FWHM of the peak corresponding to the (104) plane.
In addition, it can be seen that the cathode active material according to an embodiment is a single-crystal by confirming grains and grain boundaries of a sub-micro scale or higher when the cross-sectional microstructure thereof is identified through a SEM.
When the peak intensity ratios I(003)/I(104), and W(003)/W(104) of the cathode active material according to an embodiment are within these ranges, the stability of the crystal structure of the cathode active material may be improved and the expansion rate and contraction rate according to the insertion/release of lithium may be improved. Accordingly, the capacity characteristics of the lithium secondary battery may be improved.
The cathode active material may further comprises a cobalt compound-containing coating layer on a surface of the nickel-based lithium metal oxide.
The cobalt compound-containing coating layer may coat all or part of the surface of the cathode active material. For example, the coating layer may coat 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 1% to 10% of the surface of the cathode active material.
The content of a cobalt compound in the coating layer may be 0.1 mol % to 5.0 mol %, 0.5 mol % to 5.0 mol %, 1 mol % to 4 mol %, or 1.5 mol % to 3 mol % based on the total content (100 mol %) of the cathode active material. When the content of the cobalt compound is within the above range, in the synthesis process of the cathode active material, the reactivity between an electrolyte and the interface of the cathode active material may be decreased by reducing Ni3+ included in a metal layer in a large amount into Ni2+ and Co4+ included in the metal layer in a large amount into Co3+/Co2+ or reducing the two types of ions at the same time.
The cobalt compound-containing coating layer may include cobalt oxide, lithium cobalt oxide, or a combination thereof. In addition, the cobalt compound-containing coating layer may further include at least one selected from boron, manganese, phosphorus, aluminium, zinc, zirconium, and titanium.
The coating layer may have a thickness of about 1 nm to about 50 nm, about 5 nm to about 45 nm, or about 10 nm to about 35 nm. When the thickness of the coating layer is within the above range a cathode active material having improved surface resistance characteristics may be obtained.
Hereinafter, a method of preparing a cathode active material for a lithium secondary battery according to an embodiment will be described.
First, a nickel precursor and at least one metal precursor selected from an M1 precursor and an M2 precursor may be subjected to a co-precipitation reaction and then dried to obtain a hollow nickel-based metal precursor having pores therein. The nickel-based metal precursor may have amorphous and porous properties, and the nickel-based metal precursor may be a secondary particle, and for example, the particle size of the secondary particle may be 7 μm to 20 μm or 10 μm to 18 μm, or any ranges subsumed within 7 μm to 20 μm. When a nickel-based metal precursor having such a hollow structure is used, the amount of sintering (heat treatment) filling is increased to improve process flow, and mass production yield can be improved.
In the co-precipitation reaction, a complexing agent and a pH-adjusting agent are used.
The complexing agent may control the reaction rate of the formation of precipitates in the co-precipitation reaction, and may be ammonium hydroxide (NH4OH) (aqueous ammonia), citric acid, or a mixture thereof. The complexing agent may be used at any suitable amount generally used in the art. In one embodiment, aqueous ammonia may be used, for example, as the complexing agent.
The concentration of the complexing agent may be about 0.1 M to about 1.5 M, for example, about 0.1 M to about 1.4 M, or about 0.5 M to about 1.4 M.
The pH-adjusting agent may control the pH of the reaction mixture to form a precipitate from the reaction mixture, and examples thereof include sodium hydroxide (NaOH), sodium carbonate (Na2CO3), sodium oxalate (Na2C2O4), or a mixture thereof. The pH-adjusting agent may be, for example, sodium hydroxide (NaOH).
The M1 precursor may be the same as M1 of Formula 1 below, and may include at least one selected from a cobalt precursor, a manganese precursor, and an aluminum precursor. The M2 precursor may be the same as M2 of Formula 1 below, and may include at least one selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), and zirconium (Zr).
Lia(Ni1−x−yM1xM2y)O2±α1 Formula 1
wherein, in Formula 1, M1 may be at least one element selected from Co, Mn, and Al,
M2 may be at least one element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), and zirconium (Zr), and
0.95≤a≤1.1, 0.6≤(1−x−y)<1, 0≤x<0.4, 0≤y<0.4, and 0≤α1≤0.1, and a case where both x and y are 0, is excluded.
The metal precursor may include, for example, at least one compound selected from an aluminum precursor a cobalt precursor, a manganese precursor, and a metal (M2) precursor.
During the co-precipitation reaction, the pH of the mixture may be adjusted through two steps. The first step may be a pore formation section, in which the pH of the mixture is controlled to be about 11.5 to about 12.0. The second step may be a particle growth section, and the pH of the mixture is controlled to be, for example, about 10.5 to about 11.9. The second step is carried out at a pH lower than that of the first step. As described above, by changing a co-precipitation rate, a difference between the synthesis rate of the interior of the nickel-based metal precursor and the synthesis rate of the exterior of the nickel-based metal precursor may be caused to occur. As a result, a nickel-based metal precursor having pores therein may be obtained. In this regard, the nickel-based metal precursor refers to a precursor for obtaining a nickel-based lithium metal oxide.
In the first step, the pH of the mixture may be adjusted to be, for example, in the range of about 11.6 to about 11.9, or about 11.7 to about 11.8. In the second step, the pH of the mixture may be adjusted to be, for example, in the range of about 10.8 to about 11.7, about 11 to about 11.7, about 11.2 to about 11.6, or about 11.3 to about 11.6.
The difference between the pH of the second step and the pH of the first step may be in the range of about 0.1 to about 1.5. The difference between the pH of the second step and the pH of the first step may be in the range of, for example, about 0.1 to about 1.0, about 0.1 to about 0.8, about 0.1 to about 0.6, about 0.1 to about 0.5, about 0.1 to about 0.3, or about 0.1 to about 0.2.
The stirring time of the first step may vary depending on, for example, the pH conditions of the first step. In an embodiment, the stirring time may be in the range of, for example, about 8 hours to about 12 hours, or about 9 hours to about 10 hours.
According to the subject matter of the present disclosure, the co-precipitation reaction described above proceeds at a faster rate than a method of preparing a cathode active material precursor of the related art and thus the pore distribution of the core is controlled to be high. Accordingly, a cathode active material can be easily prepared, resulting in high productivity. When the pore distribution is controlled to be high, the number of pores in the cathode active material after heat treatment is increased, so that the active material is easily broken during pressing and excellent electrochemical properties can be exhibited in the cathode. The co-precipitation reaction can be carried out at a high speed by adjusting the stirring time to be short while the stirring speed is high. The nickel-based metal precursor having pores therein is a secondary particle containing a plurality of primary particles, and has a hollow (substantially hollow) structure having pores therein. The particle size of the secondary particles may be, for example, 7 μm to 20 μm, 10 μm to 18 μm, 12 μm to 18 μm, or 12 μm to 14 μm.
The particle size of the primary particles may be, for example, 0.2 μm to 0.3 μm (200 nm to 300 nm). When the particle sizes of the primary particles and the secondary particles of the nickel-based metal precursor having pores therein are within these ranges, the phase stability of cathode active material may be excellent or at least improved. Thus, the cathode active material having improved capacity characteristics may be obtained.
The nickel-based metal precursor having pores therein exhibits an amorphous characteristic, and contains an interior having pores and an exterior having a denser structure than the interior. The amorphous properties of the nickel-based metal precursor can be confirmed by X-ray diffraction analysis.
The term “interior,” as used herein, of the nickel-based metal precursor refers to a pore region in which a plurality of pores exist, a region corresponding to 50% by volume to 70% by volume, for example, 60% by volume of the total volume of the precursor from the center to the surface thereof, or the remaining region except for the region (exterior) within 3 μm from the outermost surface of the nickel-based metal precursor.
According to an embodiment, the interior of the nickel-based metal precursor has a pore region containing pores, and the pore region may have the longer length of, for example, 2 μm to 7 μm, for example, 3.5 μm to 5 μm.
The product obtained according to the co-precipitation reaction is dried, thereby obtaining a target nickel-based metal precursor. In this regard, the drying is performed under any suitable conditions generally used in the art. The product obtained according to the co-precipitation reaction may also be cleaned (e.g. washed with distilled water), before being dried.
The nickel precursor and at least one metal precursor of the M1 precursor and the M2 precursor may include, for example, a nickel precursor, a manganese precursor, and a cobalt precursor. In an embodiment, the metal precursor may include, for example, a nickel precursor, a cobalt precursor, and an aluminum precursor.
Examples of the nickel precursor are Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O4·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, fatty acid nickel salt, nickel halide, and a combination thereof. Examples of the manganese precursor are: manganese oxides such as Mn2O3, MnO2, and Mn3O4; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, MnSO4H2O , manganese acetate, dicarboxylic acid manganese salt, manganese citrate, and fatty acid manganese salt; a manganese oxyhydroxide; a manganese halide such as manganese chloride; and a combination thereof.
Examples of the cobalt precursor are Co(OH)2, CoOOH, CoO, Co2O3, Co3O4, Co(OCOCH3)2·4H2O, CoCl2, Co(NO3)2·.6H2O, CoSO4, Co(SO4)2·7H2O, and a combination thereof.
The aluminum precursor may be, for example, aluminum hydroxide, aluminum chloride, aluminum oxide, aluminum sulfate (Al2(SO4)3·18H2O), or a combination thereof.
Regarding the M2 precursor, the precursor containing each element may be a salt, hydroxide, oxyhydroxide, halide, or a combination thereof, each containing each element. In this regard, the salt containing an element may be, for example, at least one compound selected from sulfate, alkoxide, oxalate, phosphate, halide, oxyhalide, sulfide, oxide, peroxide, acetate, nitrate, carbonate, citrate, phthalate, and perchlorate, each including the element described above.
The amount of the nickel precursor and at least one metal precursor selected from the M1 precursor and the M2 precursor may be stoichiometrically controlled to obtain the target nickel-based metal precursor.
The nickel-based metal precursor may be a compound represented by Formula 3,
a compound represented by Formula 4, or a combination thereof.
(Ni1−x−yM1xM2y)(OH)2 Formula 3
wherein, in Formula 3, M1 may be at least one element selected from Co, Mn, and Al,
M2 may be at least one element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al), and
0.6≤(1−x−y)<1, 0≤x<0.4, and 0≤y<0.4, and a case where both x and y are 0, is excluded,
(Ni1−x−yM1xM2y)O Formula 4
wherein, in Formula 4, M1 is at least one element selected from Co, Mn, and Al,
M2 may be at least one element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al), and
0.6≤(1−x−y)<1, 0≤x<0.4, and 0≤y<0.4, and a case where both x and y are 0, is excluded.
The nickel-based metal precursor may be, for example, a compound represented by a compound of Formula 5, a compound of Formula 6, or a combination thereof.
Ni1−x−y−zCoxM3yM4z(OH)2 Formula 5
wherein, in Formula 5, M3 may be at least one element selected from Mn and Al,
M4 may be at least one element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al), and
0.6≤(1−x−y−z)<1, 0≤x<0.4, 0≤y<0.4, and 0z<0.4, and a case where x, y, and z are each 0, is excluded,
(Ni1−x−y−zCoxM3yM4z)O. Formula 6
wherein, in Formula 6, M3 is at least one element selected from Mn and Al,
M4 may be at least one element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al), and
0.6≤(1−x−y−z)<1, 0≤x<0.4, 0≤y<0.4, and 0≤z<0.4, and a case where x, y, and z are each 0, is excluded.
The nickel-based metal precursor may be, for example a compound represented by Formula 7, a compound represented by Formula 8, or a combination thereof.
Ni1−x−y−zCoxMnyM4z(OH)2 Formula 7
wherein, in Formula 7, M4 is at least one element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al), and
0.6≤(1−x−y−z)<1, 0≤x<0.4, 0≤y<0.4, and 0z<0.4, and a case where x, y, and z are each 0, is excluded,
(Ni1−x−y−zCoxAlyM4z)O Formula 8
wherein, in Formula 8, M4 may be at least one element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), and zirconium (Zr), and
00.6≤(1−x−y−z)<1, 0≤x<0.4, 0≤y<0.4, 0z<0.4, and a case where x, y, and z are each 0, is excluded.
Then, the nickel-based metal precursor having pores therein is mixed with the lithium precursor to obtain a mixture.
The mixing ratio of the lithium precursor and the nickel-based metal precursor may be stoichiometrically adjusted to prepare a desired cathode active material.
The mixture is subjected to a first heat treatment to obtain oxide particles having a porous structure. Phase change and grain growth occur through the first heat treatment.
Then, the oxide particles having a porous structure obtained through the first heat treatment are subjected to a pulverizing process to control the particle size distribution to be 1.4 or less, thereby preparing a cathode active material according to an embodiment. The particle size may be controlled to be 10 μm or less, for example, 1 μm to 10 μm, or 1 μm to 8 μm through the pulverizing process described above.
The method of preparing a cathode active material according to an embodiment may further include a second heat treatment. The second heat treatment may contribute to the formation of a cathode active material having higher crystallinity.
The first heat treatment may be performed at a higher temperature than the second heat treatment. When the first heat treatment is performed at a higher temperature than the second heat treatment, a single-crystal cathode active material with improved phase stability can be obtained.
Secondary particles have strong agglomeration between primary particles, and the term “pulverizing,” as used in the present disclosure, refers to a process performed using equipment that applies a strong force (air pressure, mechanical pressure, etc.) to remove the strong agglomeration described above, and examples of the equipment are a jet mill, and an air classifying mill (ACM). When the pulverizing process is performed with a jet mill, the air pressure may be suitably or appropriately adjusted such that the volume density of the pulverized product is 0.2 g/cm3 to 0.50 g/cm3. The air pressure may be controlled to be, for example, in the range from 2 bar to 8 bar, or from 4 bar to 6 bar.
The term pulverization, as used herein, is a term distinct from crushing, and refers to grinding of, for example, powder (particle size: 1 mm or less) into micro-scale particles (particle size: 10 μm or less). In contrast, the term crushing, as used herein, may refer to breaking up a solid (particle size: 10 mm or more) into a powder (particle size: 1 mm or less).
The nickel-based metal precursor and the lithium precursor may be mixed such that a molar ratio (Li/Me) of Li to a metal other than Li is 0.9 or more and less than 1.1, more than 1.0 and less than 1.1, 1.01 to 1.06, or 1.02 to 1.04.
The lithium precursor may be lithium hydroxide, lithium carbonate, lithium sulfate, lithium nitrate, or a combination thereof.
The first heat treatment may be performed in an oxidizing gas atmosphere, at a temperature of 800° C. to 1200° C., 900° C. to 1100° C., or 1000° C. to 1200° C., and the second heat treatment may be performed in an oxidizing gas atmosphere, at a temperature of 600° C. to 900° C., 650° C. to 850° C., 650° C. to 800° C. or 650° C. to 750° C. When the first heat treatment and the second heat treatment are performed under these conditions, a high-density and long-life lithium secondary battery can be manufactured.
The time of the first heat treatment varies depending on the temperature of the first heat treatment, and may be, for example, from 8 hours to 20 hours.
The oxidizing gas atmosphere uses an oxidizing gas such as oxygen or air, and, for example, the oxidizing gas atmosphere includes or consists of a gas atmosphere containing 90% by volume or more of oxygen.
The nickel-based metal precursor and the lithium precursor may be mixed by dry mixing, and may be performed using a mixer or the like. The dry mixing may be performed by milling. Milling conditions are not particularly limited, and may be carried out such that there is little deformation such as micronization of each precursor used as a starting material.
The particle size of the lithium precursor mixed with the nickel-based metal precursor may be controlled in advance. The particle size (e.g., average particle diameter) of the lithium precursor may be in the range of 5 μm to 15 μm. In an embodiment, the particle size of the lithium precursor may be about 10 μm. A target mixture may be obtained by milling a lithium precursor having this particle size with a nickel-based lithium metal oxide precursor at 300 to 3,000 rpm. When the temperature in the mixer rises to about 30° C. or higher in the milling process, a cooling process may be performed to maintain the temperature in the mixer at room temperature (25° C.).
After the pulverizing, the method may further comprise obtaining a mixture by adding a cobalt precursor to a pulverized product. The cobalt precursor may be used when forming a cobalt compound-containing coating layer on the surface of the nickel-based lithium metal oxide. The cobalt precursor may be Co(OH)2, CoOOH, CoO, Co2O3, Co3O4, Co(OCOCH3)2·4H2O, CoCl2, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O, or a combination thereof.
The nickel-based metal precursor may be, for example, Ni0.94Co0.05Mn0.01(OH)2, Ni0.94Co0.05Al0.01(OH)2, Ni0.92Co0.05Al0.03O2, Ni0.94Co0.03Al0.03(OH)2, Ni0.88Co0.06Al0.06(OH)2, Ni0.96Co0.02Al0.2(OH)2, Ni0.93Co0.04Al0.03(OH)2, Ni0.8Co0.15Al0.05O2(OH)2, Ni0.75Co0.20Al0.05(OH)2, Ni0.92Co0.05Mn0.03(OH)2, Ni0.94Co0.03Mn0.03(OH)2, Ni0.88Co0.06Mn0.06(OH)2, Ni0.96Co0.02Mn0.02(OH)2, Ni0.93Co0.04Mn0.03(OH)2, Ni0.8Co0.15Mn0.05(OH)2, Ni0.75Co0.20Mn0.05(OH)2, Ni0.6Co0.2Mn0.2(OH)2, Ni0.7Co0.15Mn0.15(OH)2, Ni0.7Co0.1Mn0.2(OH)2, Ni0.8Co0.1Mn0.1(OH)2, or Ni0.85Co0.1Al0.05(OH)2.
In an embodiment, the nickel-based lithium metal oxide may be, for example, LiNi0.94Co0.05Mn0.01O2, Li1.05Ni0.94Co0.05Al0.01O2, Li1.05Ni0.92Co0.05Al0.03O2, Li1.05Ni0.94Co0.03Al0.03O2, Li1.05Ni0.88Co0.06Al0.06O2, Lii1.05Ni0.96Co0.02Al0.2O2, Li1.05Ni0.93Co0.04Al0.03O2, Li1.05Ni0.8Co0.15Al0.05O2, Li1.05Ni0.75Co0.20Al0.05O2, Li1.05Ni0.92Co0.05Mn0.03O2, Li1.05Ni0.94Co0.03Mn0.03O2, Li1.05Ni0.88Co0.06Mn0.06O2, Li1.05Ni0.96Co0.02Mn0.02O2, Li1.05Ni0.93Co0.04Mn0.03O2, Li1.05Ni0.8Co0.15Mn0.05O2, Li1.05Ni0.75Co0.02Mn0.05O2, Li1.05Ni0.6Co0.2Mn0.2O2, Li1.05Ni0.7Co0.15Mn0.15O2, Li1.05Ni0.7Co0.1Mn0.2O2, Li1.05Ni0.8Co0.1Mn0.1O2, or Li1.05Ni0.85Co0.1Al0.05O2.
Another aspect of embodiments of the present disclosure provides a cathode for a lithium secondary battery, the cathode including a cathode current collector and the cathode active material.
Another aspect of embodiments of the present disclosure provides a lithium secondary battery including a cathode, an anode, and an electrolyte therebetween.
By using the method for preparing a cathode active material according to an embodiment, aggregation between particles may be suppressed or reduced and productivity may be increased, and a single-crystal cathode active material may be prepared. By using the cathode active material, a lithium secondary battery with increased density and prolonged lifespan may be manufactured.
Hereinafter, a method of manufacturing a lithium secondary battery including a cathode including a cathode active material according to an embodiment, an anode, a lithium salt-containing nonaqueous electrolyte, and a separator will be described.
The cathode and the anode are prepared by applying and drying a composition for a cathode active material layer and a composition for an anode active material layer on a cathode current collector and an anode current collector to form a cathode active material layer and an anode active material layer, respectively.
A composition for forming the cathode active material layer may be prepared by mixing a cathode active material, a conductive material, a binder, and a solvent. As the cathode active material, a nickel-based lithium metal oxide according to an embodiment may be used.
The binder in the cathode improves the adhesive strength between cathode active material particles and between the cathode active material and the cathode current collector. Examples of the binder may be polyvinylidene fluoride (PVDF), polyvinylidene fluoride and hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated-EPDM rubber, styrene-butadiene rubber (SBR), fluorine rubber, and various suitable copolymers thereof, and these compounds may be used either alone as one type or as a mixture of two or more types. The amount of the binder may be from about 1 part by weight to about 5 parts by weight based on 100 parts by weight of the total weight of the cathode active material. When the amount of the binder is within this range, the binding force of a cathode active material layer with respect to a cathode current collector may be suitable or sufficient.
The conducting agent may be any suitable material as long as it has electrical conductivity without causing a chemical change (e.g., substantially without causing an undesirable chemical change) in the corresponding battery. Examples of the conducting agent may be: graphite such as natural graphite or artificial graphite; a carbonaceous material such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fiber such as carbon fiber or metal fiber; fluorocarbon; metal powder such as aluminum powder or nickel powder; conductive whisker such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; and a conductive material such as a polyphenylene derivative.
An amount of the conducting agent may be in a range of about 1 part to about 10 parts by weight or about 1 part to about 5 parts by weight based on 100 parts by weight of the cathode active material. When the amount of the conducting agent is within these ranges, conductivity characteristics of the final cathode thus obtained may be excellent or at least improved.
A non-limiting example of the solvent may be N-methylpyrrolidone, and an amount of the solvent may be in a range of about 20 parts to about 200 parts by weight based on 100 parts by weight of the cathode active material. When the amount of the solvent is within this range, a process for forming the cathode active material layer may be easily carried out.
A thickness of a cathode current collector may be in a range of about 3 μm to about 500 μm. A material of the cathode current collector is not particularly limited as long as it has electrical conductivity without causing a chemical change in the corresponding battery. Examples of the material of the cathode current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum or stainless steel that is surface treated with carbon, nickel, titanium, or silver. The cathode current collector may have fine irregularities on a surface thereof to enhance adhesive strength to the cathode active material. The cathode current collector may be in various suitable forms, such as a film, a sheet, a foil, a net, a porous structure, a foam structure, or a non-woven structure.
Also, an anode active material, a binder, and a solvent may be mixed to prepare a composition for an anode active material layer.
As the anode active material, a material capable of reversibly intercalating/deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of being doped on and dedoped from lithium, a transition metal oxide, or a combination thereof may be used.
Examples of the material capable of reversibly intercalating/deintercalating lithium ions include a carbon material, such as, a carbon-based anode active material that is generally used in lithium secondary batteries. Examples of carbon-based anode active materials include crystalline carbon, amorphous carbon, or a combination of these. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite, which is amorphous, plate-like, flake, spherical, or fibrous, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, and calcined coke.
The alloy of lithium metal may be an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.
The material capable of being doped on and dedoped from lithium may be a silicon-based material, for example, Si, SiOx(0<x<2), a Si-Q alloy (wherein Q may be an element selected from an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and a combination thereof, and may not be Si), a Si-carbon composite, Sn, SnO2, Sn—R (wherein R may be an element selected from an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and a combination thereof, and may not be Sn), or a Sn-carbon composite, etc. In an embodiment, at least one of these and SiO2 may be mixed and used. The elements Q and R may be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.
Lithium titanium oxide may be used as the transition metal oxide.
Non-limiting examples of an anode binder are polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and polyacrylic acid, and various suitable binder polymers and/or copolymers, which are prepared by substituting hydrogen of these compounds with Li, Na, or Ca.
An anode active material layer may further include a thickening agent.
As the thickening agent, at least one of carboxymethyl cellulose (CMC), carboxyethyl cellulose, starches, regenerated cellulose, ethyl cellulose, hydroxylmethyl cellulose, hydroxylethyl cellulose, hydroxypropyl cellulose, and polyvinyl alcohol may be used. For example, the thickening agent may be CMC.
An amount of the solvent may be in a range of about 100 parts to about 300 parts by weight based on 100 parts by weight of the total weight of the anode active material. When the amount of the solvent is within this range, a process for forming the anode active material layer may be easily carried out.
The anode active material layer does not need a conductive material when conductivity is ensured. However, the anode active material layer may further include a conductive material if necessary to achieve suitable properties.
The conducting agent may be any suitable material as long as it has electrical conductivity without causing a chemical change (e.g., substantially without causing an undesirable chemical change) in the corresponding battery. Examples of the conducting agent may be: graphite such as natural graphite and artificial graphite; a carbonaceous material such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fiber such as carbon fiber and metal fiber; fluorocarbon; metal powder such as aluminum powder and nickel powder; conductive whisker such as zinc oxide and potassium titanate; conductive metal oxide such as titanium oxide; and conductive materials such as polyphenylene derivatives. The conductive material may be, for example, carbon black.
When the anode active material layer includes a conductive material, the amount of the conductive material may be from about 0.01 parts by weight to about 10 parts by weight, about 0.01 parts by weight to about 5 parts by weight, or about 0.1 parts by weight to about 2 parts by weight, based on the total weight of 100 parts by weight of the anode active material layer.
A thickness of an anode current collector may be, for example, in a range of about 3 μm to about 500 μm. A material of the anode current collector is not particularly limited as long as it has electrical conductivity without causing a chemical change in the corresponding battery. Examples of the material of the anode current collector are copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel that is surface treated with carbon, nickel, titanium, or silver, and an aluminum-cadmium alloy. Also, similar to the cathode current collector, the anode current collector may have fine irregularities on a surface thereof to enhance adhesive strength to the anode active material. The anode current collector may be in various suitable forms, such as a film, a sheet, a foil, a net, a porous structure, a foam structure, or a non-woven structure.
A separator may be located between the cathode and the anode prepared as described above.
The separator may have a pore diameter in a range, for example, of about 0.01 μm to about 10 μm and a thickness in a range of about 5 μm to about 30 μm. Examples of the separator may include an olefin-based polymer separator such as polypropylene separator or polyethylene separator; or a sheet or non-woven fabric of glass fibers. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may concurrently (e.g., simultaneously) serve as the separator.
The non-aqueous electrolyte including a lithium salt is formed of a non-aqueous electrolyte and a lithium salt. As the non-aqueous electrolyte, a non-aqueous electrolyte solution, an organic solid electrolyte, and an inorganic solid electrolyte may be used.
Examples of the non-aqueous electrolyte solution may be, but are not limited to, any suitable aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyro lactone, 1,2-dimethoxy ethane, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, N,N-formamide, N,N-dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate.
Examples of the organic solid electrolyte may be, but are not limited to, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymer, polyester sulfide, polyvinyl alcohol, and polyvinylidene fluoride.
Examples of the inorganic solid electrolyte may be, but are not limited to, a nitride of Li; a halide of Li; and a sulfate of Li, such as Li3N, LiI, Li5NI2, Li3N—LiI—LiOH, Li2SiS3, Li4SiO4, Li4SiO4—LiI—LiOH, and Li3PO4—Li2S—SiS2.
The lithium salt may be a material easily dissolved in the non-aqueous electrolyte, for example, but is not limited to, LiCI, LiBr, LiI, LiCIO4, LiBF4, LiB10Cl10, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, (FSO2)2NLi, lithium chloroborate, or a combination thereof.
Referring to
An electrode assembly in which the cathode 53, the anode 52, and the separator 54 are wound or folded, is accommodated in a battery case 55. The separator 54 may be located between the cathode 53 and the anode 52 to form a battery assembly in which the cathode 53, the anode 52, and the separator 54 are alternately stacked according to the shape of the battery 51. Next, an organic electrolyte is injected into the battery case 55 and sealed with a cap assembly 56 to complete the manufacture of the lithium secondary battery 51. The battery case 55 may have a cylindrical, rectangular, or thin-film shape. For example, the lithium secondary battery 51 may be a large-sized thin-film battery. The lithium secondary battery 51 may be a lithium ion battery. Once the battery assembly is accommodated in a pouch, impregnated in an organic electrolyte solution, and sealed, the manufacture of a lithium ion polymer battery may be completed. In addition, a plurality of the battery structures are stacked to form a battery pack, and the battery pack can be used in any suitable device requiring high capacity and high output. For example, the battery pack may be used in laptop computers, smart phones, and electric vehicles.
Also, the lithium secondary battery may be used in electric vehicles (EVs) due to excellent storage stability at high temperature, lifespan characteristics, and high-rate characteristics. For example, the lithium secondary battery may be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs).
One or more embodiments will now be described in more detail with reference to the following examples. However, these examples are not intended to limit the scope of the one or more embodiments.
A nickel-based metal precursor (Ni0.94Co0.05Mn0.01(OH)2) (NCM precursor) was synthesized through co-precipitation.
Nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water, which is a solvent, such that a molar ratio of Ni:Co:Mn 94:5:1 to prepare a mixed solution. An aqueous ammonia (NH4OH), which is a complexing agent, and sodium hydroxide (NaOH), which is a pH adjuster, were prepared to form a complex compound. The concentration of aqueous ammonia was 0.5 M, and the concentration of sodium hydroxide was 32 wt %. The metal source mixed solution, aqueous ammonia, and sodium hydroxide were added into a reactor. Sodium hydroxide was then added into the reactor to adjust the pH of the inside thereof.
The pH of the mixture was adjusted to be 11.75 and stirred for 10 hours, and then the pH of the mixture was adjusted to be 11.55 and stirred for 25 hours to reduce the pH by about 0.2 based on the initial pH. In this way, by changing the co-precipitation rate of the nickel-based lithium metal oxide precursor, the difference was caused to occur between the synthesis rate of the interior of the nickel-based lithium metal oxide precursor and the exterior thereof, thereby obtaining a nickel-based lithium metal oxide precursor having pores therein.
After the reaction was carried out for about 20 hours while stirring the reaction mixture, the input of the raw material solution was stopped.
The slurry solution in the reactor was filtered and washed with distilled water of high purity and dried in a hot air oven at 200° C. for 24 hours to obtain a nickel-based lithium metal oxide precursor (Ni0.94Co0.05Mn0.01(OH)2) having a hollow structure. The nickel-based metal precursor is a secondary particle that is an aggregate of primary particles, and the particle size of the primary particles was about 300 nm (0.3 μm), and the average particle diameter of the secondary particles was about 14 μm.
A nickel-based metal precursor (Ni0.94Co0.05Al0.01(OH)2) (NCA precursor) was synthesized through co-precipitation.
A nickel-based lithium metal oxide precursor (Ni0.94Co0.05Al0.01(OH)2) having a hollow structure was obtained in the same manner as in Preparation Example 1, except that aluminum sulfate (Al2(SO4)318H2O) was used instead of manganese sulfate in preparing the mixed solution. The nickel-based metal precursor is a secondary particle that is an aggregate of primary particles, and the particle size of the primary particles was about 300 nm (0.3 μm), and the average particle diameter of the secondary particles was about 14 μm.
A large-grain nickel-based metal precursor that had a dense state and did not have a hollow structure was obtained in the same manner as in Preparation Example 1, except that the pH of the mixture was maintained at 11.77 and stirred for a total of 35 hours, instead of reducing the pH of the mixture by about 0.2 based on the initial pH in such a manner that the pH of the mixture was adjusted to be 11.75 and then stirred for 10 hours, and then, the pH of the mixture was adjusted to be 11.55 and stirred for 25 hours. The nickel-based metal precursor obtained according to Comparative Preparation Example 1 is a secondary particle that is an aggregate of primary particles, and the particle size of the primary particles was about 300 nm (0.3 μm), and the average particle diameter of the secondary particles was about 14 μm.
A large particle nickel-based metal precursor that had a high-density state and did not have a hollow structure, was obtained in the same manner as in Preparation Example 2, except that the pH of the mixture was maintained at 11.77 and stirred for a total of 35 hours, instead of reducing the pH of the mixture by about 0.2 based on the initial pH in such a manner that the pH of the mixture was adjusted to be 11.75 and then stirred for 10 hours, and then, the pH of the mixture was adjusted to be 11.55 and stirred for 25 hours. The nickel-based metal precursor obtained according to Comparative Preparation Example 2 is a secondary particle that is an aggregate of primary particles, and the particle size of the primary particles was about 300 nm (0.3 μm), and the average particle diameter of the secondary particles was about 14 μm.
Comparative Preparation Example 3: Small Particle, High-Density, and non-Hollow NCM Precursor
A high-density small particle nickel-based metal precursor having a dense state without a hollow structure was obtained in the same manner as in Comparative Preparation Example 1, except that the pH of the mixture was increased from 11.77 to 12.2. The average particle diameter of the secondary particles of the small particle nickel-based metal precursor was about 3 μm.
The porous nickel-based metal precursor (Ni0.94Co0.05Mn0.01(OH)2) having a hollow structure of Preparation Example 1 and lithium hydroxide were added to obtain a first mixture. The molar ratio (Li/Me) of Li to the metal other than Li in the first mixture was about 1.02. In this regard, the amount of metal (Me) was the total amount of Ni, Co and Mn.
The first mixture was subjected to a first heat treatment at 900° C. in an air atmosphere for 15 hours to prepare hollow and crystallized secondary particles (SP) (see, for example,
The first heat treatment product was pulverized by using a jet mill to obtain pulverized particles having a particle size of 3 μm. The air pressure during jet-mill pulverizing was about 5 bar. These particles were surface-defected primary particles (PP) (see
A single-crystal (SC) cathode active material (Li1.02Ni0.94Co0.05Mn0.01O2) was prepared by performing a second heat treatment on the pulverized particles in an oxygen atmosphere at about 750° C. (see
The particle size (e.g., average particle diameter) of the single-crystal particles (one body particle or primary particle) of the cathode active material was about 3 μm, and the single-crystal particles had a non-porous structure.
A first mixture was obtained by adding nickel-based metal precursor (Ni0.94Co0.05Al0.01(OH)2) having a hollow structure of Preparation Example 2 and lithium hydroxide. The molar ratio (Li/Me) of Li to the metal other than Li in the first mixture was about 1.02. In this regard, the metal (Me) amount was the total amount of Ni, Co and Al.
The first mixture was subjected to a first heat treatment at 900° C. in the air atmosphere for 15 hours to prepare crystalline secondary particles (SP) having a hollow structure. Through the first heat treatment, Ni antisite was formed in the bulk structure and nickel was diffused to the surface to form NiO phase that is irreversible in terms of electrochemical activity.
The first heat treatment product was pulverized by using a jet mill to obtain pulverized particles having a particle size of 3 μm. These particles were surface-defected primary particles (PP).
A cathode active material (LiNi0.94Co0.05Al0.01O2) containing a cobalt compound-containing coating layer having a hollow structure was prepared by adding Co(OH)2, which is a cobalt precursor, to the pulverized particles and performing a second heat treatment at about 700° C. in an oxygen atmosphere. The amount of the cobalt precursor was controlled such that the amount of the cobalt compound in the cobalt compound-containing coating layer was 2 mol % based on the total amount of the cathode active material.
The cathode active material obtained according to Example 1 contained single-crystal particles, the particle size of the single-crystal particles was about 3 μm, and the cathode active material had a non-porous structure. The amount of the cobalt compound was 2 mol % based on the total amount of the cathode active material finally obtained, and the thickness of the cobalt compound-containing coating layer was about 20 nm.
The cobalt compound-containing coating layer improves the surface stability and ionic conductivity of the single-crystal cathode active material, and the presence of the coating layer containing the cobalt compound was confirmed by the EDS-mapping of
Example 3 relates to a case in which the cathode active material of Example 2 was prepared in lab-scale and mass-scale production (MP), and is an experimental example for mass productivity test of Evaluation Example 6 to be described below.
In the lab-scale experiment, 200 g of precursor was mixed with lithium hydroxide (LiOH) and heat treated in a box-furnace. In the MP scale, 3,000 g of precursor was mixed with LiOH and heat treated in Roller Hearth Kiln (RHK). The precursor used herein was the nickel-based metal precursor (Ni0.94Co0.05Al0.01(OH)2) having a hollow structure used in Example 2.
In the lab-scale test and the MP-scale tests, the first heat-treated mixture SP was pulverized using a jet mill. 200 g of powder was subjected to the second heat treatment in a box furnace to obtain SC-Lab (single-crystal cathode active material prepared in lab-scale test). Then, 3,000 g of powder was subjected to the second heat treatment at RHK to obtain SC-MP (single-crystal cathode active material prepared in mass-scale production test). In Example 3, the conditions for each of the first heat treatment and the second heat treatment were in the same as described in Example 2.
A first mixture was obtained by adding nickel-based metal precursor (Ni0.94Co0.05Mn0.01(OH)2) having a non-hollow structure of Comparative Preparation Example 1 and lithium hydroxide. The molar ratio (Li/Me) of Li to the metal other than Li in the first mixture was about 1.02. In this regard, the metal (Me) amount was the total amount of Ni, Co and Mn.
The first mixture was subjected to a first heat treatment in an air atmosphere at 900° C. for 15 hours.
The heat treatment product was pulverized using a Hosogawa jet mill (Blower 35 Hz, AFG 8000 rpm, Air 4 kgf/cm2) to prepare a polycrystalline nickel-based lithium metal oxide having a non-hollow structure.
The pulverized nickel-based lithium metal oxide having a non-hollow structure was subjected to a second heat treatment at about 750° C. in an oxygen atmosphere to obtain a cathode active material which is polycrystalline particles and has a non-hollow structure.
Although the cathode active material obtained according to Comparative Example 1 had the form of pulverized primary particles, the surface thereof had many defects generated in the pulverizing process and the particles were broken.
A cathode active material was obtained in the same manner as in Example 1, except that the small, high-density nickel-based metal precursor of Comparative Preparation Example 3 was used instead of the large nickel-based metal precursor having the non-hollow structure of Comparative Preparation Example 1.
A polycrystalline cathode active material (Poly NCA: PC NCA) was obtained in the same manner as in Comparative Example 1, except that the nickel-based metal precursor (Ni0.94Co0.05Al0.01(OH)2) having the non-hollow structure of Comparative Preparation Example 2 was used instead of the nickel-based metal precursor (Ni0.94Co0.05Mn0.01(OH)2) having the non-hollow structure of Comparative Preparation Example 1. This cathode active material is a secondary particle and has a particle size of about 14 μm, and the particle size of a primary particle thereof was 500 nm.
The cathode active material obtained according to Comparative Example 3 was in the form of secondary particles which are polycrystalline particles with no hollow structure therein and in which primary particles were dense.
Lithium secondary battery Manufacture Example
A coin half-cell was prepared as follows without a separate pulverization process, by using the cathode active material obtained according to Example 1 as a cathode active material.
A mixture of 96 g of the nickel-based active material (LiNi0.94Co0.05Mn0.01O2) prepared in Example 1, 2 g of polyvinylidene fluoride, 47 g of N-methylpyrrolidone as a solvent, and 2 g of carbon black as a conducting agent was mixed by using a mixer to remove bubbles, thereby preparing a slurry for forming a cathode active material layer in which the mixture was homogeneously dispersed.
The slurry prepared according to the process was coated on an aluminum foil using a doctor blade so as to form a thin electrode plate, and the thin electrode plate was dried at 135° C. for 3 hours or more and subjected to pressing and vacuum drying processes, thereby preparing a cathode.
A 2032 type coin cell was manufactured using the cathode and a lithium metal counter electrode. A separator having a thickness of about 16 μm and formed of a porous polyethylene (PE) film was located between the cathode and the lithium metal counter electrode, and an electrolyte solution was injected to manufacture the 2032 type coin cell. A solution in which 1.1 M LiPF6 was dissolved in a solvent prepared by mixing ethylene carbonate (EC) and ethylmethyl carbonate (EMC) at a volume ratio of 3:5 was used as the electrolyte solution.
When a coin cell is manufactured according to Preparation Example 1, it is not necessary to go through a grinding process when manufacturing a cathode, and primary particles that are agglomerated in the pressing process may be dispersed. Therefore, productivity can be improved.
Coin half cells were manufactured in the same manner as in Manufacture Example 1, except that the cathode active materials of Examples 2 and 3 were used instead of the cathode active material of Example 1.
A coin half-cell was manufactured in the same manner as in Manufacture Example 1, except that the cathode active material obtained according to Comparative Example 1 was used instead of the cathode active material of Example 1.
A coin cell was manufactured in the same manner as in Comparative Manufacture Example 1 except that the cathode active material of Comparative Example 2 was used instead of the cathode active material of Comparative Example 1.
A coin cell was manufactured in the same manner as in Comparative Manufacture Example 1 except that the cathode active material of Comparative Example 3 was used instead of the cathode active material of Comparative Example 1.
A SEM analysis was performed on the surface and cross-section of each of the nickel-based metal precursors prepared according to Preparation Example 1 and Comparative Preparation Example 1. As the scanning electron microscope, Magellan 400L (FEI company) was used. The SEM analysis result of the surface of the nickel-based metal precursor prepared according to Preparation Example 1 is shown in
Referring to
In contrast, as shown in
SEM analysis was performed on the product (SP) obtained after the first heat treatment according to Example 1 and Comparative Example 1. The SEM was Magellan 400L (FEI company), and the SEM analysis result of the surface of the product (SP) obtained after the first heat treatment according to Example 1 is shown in
SP of Example 1 was a secondary particle including single-crystal primary particles as shown in
In contrast, the SP of Comparative Example 1 had the form of small particles (1 μm -5 μm) as shown in
In Example 2, the surface of the post-pulverizing product (PP) and the product after the second heat treatment (SC) was subjected to SEM analysis. The results of surface analysis of the pulverized product (PP) are shown in
Referring to these drawings, Ni antisite was formed in the bulk structure through the first heat treatment and nickel was diffused to the surface to form NiO that is irreversible in electrochemical activity. Due to the second heat treatment, the decrease in crystallinity in the grinding process of the second heat treatment may be recovered, and through this process, the ordering of the Ni antisite into a metal site may be promoted and surface defects may be healed or reduced. The cobalt compound-containing coating layer improves the surface stability and ionic conductivity of the single-crystal cathode active material, and the presence of the coating layer containing the cobalt compound was confirmed by the EDS-mapping of
The particle size distribution characteristics of the cathode active materials (SC) prepared according to Example 1 and Comparative Example 1 were analyzed using a particle size analyzer (PSA), and the results thereof are shown in
In Table 1, particle size distribution (span is represented by (D90-D10)/D50.
The particle size distribution graph may be obtained by the following PSD (particle size distribution) measurement conditions.
LS13320 (Beckmann Coulter) was used as a laser particle size analyzer, and the analysis conditions were as follows:
pump speed (55%), sample ultrasonic dispersion of 40 KHz ultrasonic wave (60s), run length of 60s, refractive index ratio of Sample RI 1.6, e-factor of 1.00, sample amount of 0.20 g, and 1 ml of sample input dispersant: 10% sodium hexa metaphosphate (sodium hexamethaphosphate)
Referring to Table 1 and
The particle size distribution characteristics of SP, PP, and SC obtained according to each step according to Example 2 were analyzed using a PSA, and the results thereof are shown in Table 2, and
As shown in Table 2, the span was 1.20, which indicates that SC had a uniform (substantially uniform) particle distribution.
The D50 particle size of the NCA(OH)2 precursor was 14.31 μm, and the D50 particle size of the product SP obtained after the first heat treatment was slightly increased to 15.50 μm, and as shown in
The pulverizing of SP into PP can be clearly observed from
The particle size distribution of SC NCA was slightly broadened compared to that of PP as shown in
A charging test was performed on 5 kg of the first heat-treated product according to Example 1 and Comparative Example 2, and the test results are shown in Table 3,
Referring to Table 3 and
On the other hand, when the large grain precursor of Example 1 was used, the product subjected to the first heat treatment did not show separations of top and bottom, aggregates were small, and there was no difference (substantially no difference) in XRD properties. Accordingly, it can be seen that when the large precursor of Example 1 was used, a uniform (substantially uniform) cathode active material layer having no difference in physical properties could be obtained, compared to the case using the small precursor of Comparative Example 2.
The SP, PP, and SC prepared according to Example 2 were subjected to X-ray diffraction analysis using X'pert pro (PANalytical) using Cu Karadiation (1.54056Å). The results of X-ray diffraction analysis are shown in
The crystal structure of the product in each process was analyzed by XRD characterization in
The shifting of the peak to a lower angle indicates that the well-crystallized SP particles collapsed in the PP due to the physical damage caused by the jet mill process. The FWHM of the (003) plane supports the crystal structure collapse in PP. The broadening of the FWHM may be derived mainly from the lack of crystallinity, which is depleted of the order of the lattice domains.
The loss of crystallinity from the pulverizing process can be recovered during the second heat treatment as observed from the FWHM and XRD properties of (003) plane of SC. The peak corresponding to the (003) plane shifts to the original position of the SP and the FWHM is decreased to similar value with SP exhibiting the defected crystal recovers its crystallinity. The Li/Ni disordering is decreased during the second heat treatment as the intensity ratio of (003) plane and (104) plane is increased to 1.21. The width ratio of (003) plane and (104) plane are also increased in SC. This result indicates or at least suggests that SC exhibits high crystallinity not only in the (003) plane direction but also in the (104) plane direction. XRD analysis results show that SC obtained according to the method described above had high crystallinity and low Li/Ni disordering.
In Table 4,I(003) indicates the intensity of the peak corresponding to the (003) plane (the peak having 2θ of about 18°-19°), and I(104) indicates the intensity of the peak corresponding to the (104) plane (the peak having 2θ of about)44.5°). In this regard, W(003) represents the FWHM of the peak corresponding to the (003) plane, and W(104) represents the FWHM of the peak corresponding to the (104) plane.
Charge/discharge characteristics of the coin half cells manufactured in Manufacture Example 3 and Comparative Manufacture Example 3 were evaluated using a charging/discharging apparatus (Model No.: TOYO-3100 available from TOYO).
In the first charge/discharge cycle, the coin cells were each charged at 25° C. at a constant current of 0.1 C until the voltage reached 4.25 V and then charged at a constant voltage until the current reached 0.05 C. Once the charging was completed, the cell was rested for about 10 minutes, and then discharged at a constant current of 0.1 C until the voltage reached 3 V. In the second charge/discharge cycle, the cells were each charged at a constant current of 0.2 C until the voltage reached 4.25 V and then charged at a constant voltage until the current reached 0.05 C. Once the charging was completed, the cell was rested for about 10 minutes, and then discharged at a constant current of 0.2 C until the voltage reached 3 V.
Evaluation of the lifespan of each of the coin cells was performed by charging the cell at a constant current of 1 C until the voltage reached 4.3 V and then charging the cell at a constant voltage until the current reached 0.05 C. Once the charging was completed, the cell was rested for about 10 minutes, and then discharged at a constant current of 1 C until the voltage reached 3 V. The charge/discharge cycle was repeated 50 times.
The capacity retention ratio (CRR) was calculated using Equation 3, and the charge/discharge efficiency was calculated from Equation 3. In addition, the CRR, charge/discharge efficiency characteristics, and battery capacity were evaluated and shown in
CRR[%]=[discharge capacity in 50th cycle/discharge capacity in 1st cycle]×100
Charging/discharging efficiency=[discharge voltage of 1st cycle/charging voltage of 1st cycle]×100
Referring to
Example 3 showed stable discharge capacities of 211 mAh/g and 210 mAh/g, respectively. However, while the first cycle efficiency of SC is less than 89%, the efficiency of poly NCA (PC NCA) used in Comparative Manufacture Example 3 is more than 90%. These results are due to a long diffusion path of Li+ ions through single grain (one body particles)(>μm scale). Despite the loss of primary efficiency, both SC samples showed much better cycle retention properties after 50 cycles in which 96% of the initial discharge capacity was maintained, whereas Poly NCA (PC NCA) showed 91° A of the capacity retention ratio after 50 cycles at the current rate of 1C. Considering that SC-Lab and SC-MP exhibit similar electrochemical behavior, it can be seen that when the mass-production method of SC was used, material properties with excellent physical and electrochemical properties can be obtained.
Evaluation Example 6: Lifespan at a temperature of 45° C.
Charge/discharge characteristics of the coin half cells manufactured in Manufacture Example 1 and Comparative Manufacture Example 1 were evaluated using a charging/discharging apparatus (Model No.: TOYO-3100 available from TOYO).
In the first charge/discharge cycle, the coin cells were each charged at 45° C. at a constant current of 0.1 C until the voltage reached 4.25 V and then charged at a constant voltage until the current reached 0.05 C. Once the charging was completed, the cell was rested for about 10 minutes, and then discharged at a constant current of 0.1 C until the voltage reached 3 V. In the second charge/discharge cycle, the cells were each charged at a constant current of 0.2 C until the voltage reached 4.2 V and then charged at a constant voltage until the current reached 0.05 C. Once the charging was completed, the cell was rested for about 10 minutes, and then discharged at a constant current of 0.2 C until the voltage reached 3 V.
Evaluation of the lifespan of each of the coin cells was performed by charging the cell at a constant current of 1 C until the voltage reached 4.2 V and then charging the cell at a constant voltage until the current reached 0.05 C. Once the charging was completed, the cell was rested for about 10 minutes, and then discharged at a constant current of 1 C until the voltage reached 3 V. The charge/discharge cycle was repeated 2000 times.
The CRR characteristics of the battery were evaluated and results thereof are shown in
Referring to
Charge/discharge characteristics of the coin half cells manufactured in Manufacture Example 2 and Comparative Manufacture Example 3 were evaluated using a charging/discharging apparatus (Model No.: TOYO-3100 available from TOYO).
In the first charge/discharge cycle, the coin cells were each charged at 25° C. at a constant current of 0.1 C until the voltage reached 4.25 V and then charged at a constant voltage until the current reached 0.05 C. Once the charging was completed, the cell was rested for about 10 minutes, and then discharged at a constant current of 0.1 C until the voltage reached 3 V. In the second charge/discharge cycle, the cells were each charged at a constant current of 0.2 C until the voltage reached 4.25 V and then charged at a constant voltage until the current reached 0.05 C. Once the charging was completed, the cell was rested for about 10 minutes, and then discharged at a constant current of 0.2 C until the voltage reached 3 V.
Evaluation of the lifespan of each of the coin cells was performed by charging the cell at a constant current of 1 C until the voltage reached 4.3 V and then charging the cell at a constant voltage until the current reached 0.05 C. Once the charging was completed, the cell was rested for about 10 minutes, and then discharged at a constant current of 1 C until the voltage reached 3 V. This charge/discharge cycle was repeated 200 times. In addition, ex-situ XRD analysis was performed on the (003) peak of the cathode active material before and after 200 cycles at the cathode of Manufacture Example 2 and Comparative Manufacture Example 1.
The morphology of the cathode before and after 200 cycles was analyzed using SEM.
The physical and structural changes of the Poly NCA (PC NCA) of Comparative Manufacture Example 3 and the SC NCA of Manufacture Example 3 are shown in
After 200 cycles, the morphology collapses seriously as shown in
In contrast, SC NCA retains the grain morphology of pristine electrode even after 200 cycles as shown in
As can be seen from
The single-crystal structure of NCA may withstand mechanical deformation due to expansion and contraction of the lattice during charging and discharging. Due to the narrower surface area of SC, reactions from surface such as SEI formation and NiO transformation can also be suppressed or reduced. Due to the excellent structural and morphological retention properties of SC, SC electrodes exhibit excellent or at least improved cycle retention properties.
(2) Manufacture Example 1 and Comparative Manufacture Example 1
In contrast, for the coin half cells of Manufacture Example 1 and Comparative Manufacture Example 1, the evaluation method in which the physical and structural changes of the cathode after the charge/discharge cycle for the coin half-cell of Manufacture Example 2 were identified, was performed in the same manner so as to evaluate the physical and structural changes of the cathode after the charge/discharge cycle.
As a result of the evaluation, it was confirmed that the morphology of the battery of Manufacture Example 1 did not change significantly after 200 cycles as in the case of Manufacture Example 2. In contrast, the coin half-cell of Comparative Manufacture Example 1 showed a change in morphology.
The overwhelming cyclic performance of SC over poly crystal (PC) NCA was confirmed by a full cell test.
As a cathode, an SC mixed electrode (small SC NCA+large PC NCA in a 3:7 mixing weight ratio) and a PC mixed electrode (small PC NCA+large PC NCA in a 3:7 mixing weight ratio) were each formed, and then, full cells were manufactured by using the cathodes. In this regard, small SC NCA is the cathode active material of Example 2 formed from the nickel-based metal precursor of Preparation Example 2, large PC NCA is the cathode active material of Comparative Example 3 formed from the nickel-based metal precursor of Comparative Preparation Example 2, small PC NCA is the cathode active material of Comparative Example 2 formed from the nickel-based metal precursor of Comparative Preparation Example 3. The particle size of large PC NCA was about 14 μm, and the particle size of small SC NCA and small PC NCA were both about 3 μm.
A mixture of 96 g of cathode, 2 g of polyvinylidene fluoride, 47 g of N-methylpyrrolidone as a solvent, and 2 g of carbon black as a conductive agent was mixed by using a mixer to remove bubbles, thereby preparing a slurry for forming a cathode active material layer in which the mixture was homogeneously dispersed.
The slurry prepared according to the above process was coated on an aluminum foil by using a doctor blade to form a thin electrode plate, and then dried for 3 hours or more at 135° C., followed by pressing and vacuum drying to complete the manufacture of a cathode.
98 wt % of synthetic graphite (BSG-L, Tianjin BTR New Energy Technology Co., Ltd.), 1.0 wt % of styrene-butadiene rubber (SBR) binder (ZEON), and 1.0 wt % of carboxymethylcellulose (CMC, NIPPON A&L) were mixed and then added to distilled water and stirred for 60 minutes using a mechanical stirrer to prepare an anode active material slurry. The slurry was applied to a thickness of about 60 μm on a copper current collector having a thickness of 10 μm by using a doctor blade, dried in a hot air dryer at 100° C. for 0.5 hours, and then dried again under vacuum and at a temperature of 120° C. for 4 hours, followed by roll pressing, thereby manufacturing an anode.
A full cell was prepared using the anode and the cathode. A separator having a thickness of about 16 μm and formed of a porous polyethylene (PE) film was placed between the cathode and the anode, and an electrolyte solution was injected to manufacture a 2032 type coin cell. A solution in which 1.1 M LiPF6 was dissolved in a solvent in which ethylene carbonate (EC) was mixed with ethylmethyl carbonate (EMC) at a volume ratio of 3:5, was used as the electrolyte solution.
The excellent electrochemical activity of SC was confirmed by mixing each of small PC NCA and small SC NCA with large grain PC NCA to form a SC mixed electrode and a PC mixed electrode, each of which is a bimodal electrode. Such a bimodal electrode exhibits increased electrode density and the amount of the binder may be reduced. In this regard, the mixed weight ratio of large PC and SC is 70 wt %:30 wt %, and the weight ratio of the counter electrode blended with small PC is the same. In order to equalize the titration of the current density applied to each electrode, the two blend electrodes were calendared at an electrode density of 3.65 g/cc as shown in
The SC mixed electrode (small SC NCA+large PC NCA) showed a large discharge capacity retention ratio of 91.4% after 2000 cycles at 25° C. (RT), whereas the PC mixed electrode (small particle PC (3 μm or less)+large (14 μm or less) PC NCA) had only 80% capacity retention as shown in
In addition, the manufacturing process of SC and PC-blend full cell was analyzed using in-situ chromatography, and the results are shown in
Both SC and PC cells showed similar gas generation behavior through the formation process and generated CO2 gas. Referring to
When gas emissions are reduced using SC materials, large-scale batteries with improved safety can be developed. In general, in large-scale batteries, such as EVs or ESSs, gas emissions are a major obstacle. By using a single-crystal material, a battery having not only a long lifespan but also the enhanced safety can be obtained.
The cathode active material for a lithium secondary battery according to an aspect of one or more embodiments of the present disclosure has a single-crystal characteristic capable of high capacity, and when the cathode active material is used, a lithium secondary battery having improved long life cycle stability is able to be manufactured in mass production.
It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. While one or more embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the following claims, and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2021-0116497 | Sep 2021 | KR | national |
