Patent Grant
10862119
This application claims the benefit under 35 U.S.C. § 119 of Korean Patent Application Nos. 10-2017-0152449, filed Nov. 15, 2017; 10-2017-0152450, filed Nov. 15, 2017; 10-2017-0152451, filed Nov. 15, 2017; and 10-2018-0126427, filed Oct. 23, 2018, the disclosures of each of which are incorporated herein by reference in their entirety.
The present invention relates to a cathode active material for a secondary battery and a preparation method thereof, and more particularly, to a lithium composite oxide including a secondary particle formed as primary particles cohere, in which a manganese (Mn) oxide is present in the periphery of the primary particles, a concentration of a Mn oxide has a concentration gradient from the center of the primary particle to a surface of the particle, a concentration of a Mn oxide has a concentration gradient from a surface of the secondary particle to the center thereof, and a lithium ion migration path is included in the primary particle, and a preparation method thereof.
Lithium secondary batteries, which were developed in early 1990s and have so far been used, are compact, light-weight, and large-capacity batteries spotlighted as power sources for portable devices. The lithium secondary batteries have advantages in that an operating voltage is high and energy density is significantly high, as compared with conventional batteries such as nickel-hydrogen (Ni—MH), nickel-cadmium (Ni—Cd), sulfuric acid-lead batteries using an aqueous electrolyte. In particular, recently, research into a power source for an electric vehicle in which an internal combustion engine and a lithium secondary battery are hybridized have actively been conducted in the United States, Japan, Europe, and the like.
Manufacturing large-sized batteries for electric vehicles using lithium secondary batteries has been considered in terms of energy density, but nickel-metal hydride batteries are still used in electric vehicles in consideration of safety. Lithium secondary batteries have limitations to be applied to electric vehicles due to high price and safety issues. Particularly, when lithium secondary batteries including currently commercialized LiCoO2 or LiNiO2 as a cathode active material are heated in an over-charged state, a structure thereof is rapidly changed. Thereafter, due to the structural change, oxygen in a lattice is emitted to result in an unstable crystal structure due to delithiation at the time of charging. That is, the commercialized lithium secondary batteries are very vulnerable to heat.
In order to improve this, attempts have been made to replace a portion of nickel with a transition metal element to further increase a heating start temperature or to inhibit rapid heating. A material of LiNi1−xCoxO2 (x is 0.1 to 0.3) in which a portion of nickel is replaced with cobalt exhibits excellent charge/discharge characteristics and life characteristics, but still involves the problem of thermal stability. In addition, Li—Ni—Mn composite oxides in which manganese, instead of nickel, is partially substituted or Li—Ni—Mn—Co composite oxides in which nickel is substituted with manganese and cobalt and techniques related to preparation thereof have also been developed. In this regard, Japanese Patent No. 3890185 discloses a new concept of a cathode active material which creates a solid solution by uniformly dispersing manganese and nickel compounds at an atomic level, rather than a concept of partially substituting a transition metal for LiNiO2 or LiMnO2. European Patent No. 0 918 041 and U.S. Pat. No. 6,040,090 disclose a Li—Ni—Mn—Co composite oxide in which nickel is substituted with manganese and cobalt. The composite oxide disclosed in this document has improved thermal stability, as compared with a material including only nickel and cobalt, but it can be seen that it does not completely solve the problem of thermal stability of the nickel-based compound.
In order to solve such a problem, a method of changing a surface composition of a cathode active material in contact with an electrolyte using a method such as coating a surface, or the like, has been proposed. A coating amount for coating the cathode active material is as small as 1 to 2 wt % or less with respect to the cathode active material. A small amount of coating material forms a very thin film layer of about several nanometers to inhibit a side reaction with an electrolyte or, after the coating material is applied, it is heat-treated to form a solid solution on a surface of a particle to have a metal composition different from that of the inside of the particle. Here, the particle surface layer bonded with the coating material is as thin as tens of nanometers or less, and a significant difference in composition between the coating layer and the particle bulk reduces the effect when the battery is used for a long period of time by hundreds of cycles. Further, the effect of the battery is also reduced even by incomplete coating that the coating layer is not uniformly distributed on the surface.
In this connection, Korean Patent Laid-Open Publication No. 10-2005-0083869 discloses a lithium transition metal oxide having a concentration gradient of a metal composition. In this document, however, metal compositions of an internal layer and an external layer of a synthesized oxide are different, the metal compositions are not gradually changed in a generated cathode active material. This may be solved through a heat treatment process, but, at a high temperature of 850° C. or higher, a concentration gradient difference is rarely formed due to thermal diffusion of metal ions.
(Patent document 1) Japanese Patent No. 3890185
(Patent document 2) European Patent No. 0 918 041
(Patent document 3) U.S. Pat. No. 6,040,090
(Patent document 4) Korean Patent Laid-Open Publication No. 10-2005-0083869
An aspect of the present invention provides a novel compound in which a manganese (Mn) compound has a concentration gradient in a primary particle and a secondary particle, and a preparation method thereof.
According to an aspect of the present invention, there is provided a cathode active material for a secondary battery, including: a secondary particle formed as a plurality of primary particles cohere and including a manganese oxide on a surface portion of each of the primary particles.
The cathode active material for a secondary battery according to the present invention may include a manganese (Mn) oxide between the primary particles inside the secondary particle. The cathode active material for a secondary battery according to the present invention may include a Mn oxide even at a boundary between the primary particles constituting the secondary particle.
In the cathode active material for a secondary battery according to the present invention, a Mn concentration at the surface portion of the primary particle may be higher than a Mn concentration inside the primary particle.
In the cathode active material for a secondary battery according to the present invention, the Mn concentration of the primary particle may have a gradient from a central portion to the surface portion of the primary particle.
In the cathode active material for a secondary battery according to the present invention, the Mn oxide may be selected from the group consisting of Li2MnO3, LiMn2O4, MnO2, LiwMn2O4 (0<w<1), and Li2MnO3(1−v)LiMn2O4 (0<v<1). In the case of the cathode active material for a secondary battery according to the present invention, after an active material not including Mn is prepared, Mn is present on a surface of the secondary particle and inside the secondary particle, specifically, at the boundary between the primary particles in the secondary particle in the process of rinsing the active material with a solution including Mn, and thereafter, Mn is oxidized during sintering to form an Mn oxide. The cathode active material for a secondary battery according to the present invention includes the Mn oxide selected from the group consisting of Li2MnO3, LiMn2O4, MnO2, LiwMn2O4 (0<w<1), and Li2MnO3(1−v)LiMn2O4 (0<v<1) by a bonding ratio of Mn and oxygen (O).
The cathode active material for a secondary battery according to the present invention may have peaks at positions of (020), (003), (101), (006), (102), (104), (005), (009), (107), (018), (110), and (113) when XRD-analyzed.
The cathode active material for a secondary battery according to the present invention may have the peak (020) based on Li2MnO3 between 2θ=20° and 21° when XRD-analyzed.
The cathode active material for a secondary battery according to the present invention may have a peak of Li1−xMn2O4 between 2θ=36 and 38°, between 44 and 45°, and between 65 and 66°, when XRD-analyzed.
A peak intensity increase rate at the position (104) of the cathode active material for a secondary battery according to the present invention when XRD-analyzed after charging may be 3% or less, as compared with XRD analysis before charging.
The cathode active material for a secondary battery according to the present invention may include a lithium ion migration path arranged toward the center of the secondary particle in the primary particle.
The Mn oxide of the cathode active material for a secondary battery according to the present invention may be present within 1 μm from the surface of the secondary particle.
The cathode active material for a secondary battery according to the present invention may be represented by Chemical Formula 1 below.
Li1+aNi1−(x+y+z)CoxAlyMnzM1bO2 [Chemical Formula 1]
(Here, 0≤x≤0.1, 0≤y≤0.02, 0≤z≤0.0006, 0≤a≤0.1, 0≤b≤0.1 and M1 is one or more elements selected from the group consisting of Al, Ni, Mn, Cr, Fe, Mg, Sr, V, Zn, W, Zr, B, Ba, Sc, Cu, Ti, Co, a rare earth element, and combinations thereof).
According to another aspect of the present invention, there is provided a secondary battery including a cathode active material for a secondary battery.
According to another aspect of the present invention, there is provided a method for preparing a cathode active material for a secondary battery, including: a first operation of preparing a precursor including nickel and cobalt; a second operation of adding a lithium compound and an aluminum compound to the precursor and performing a heat-treatment on the mixture to prepare a composite metal compound; and a third operation of rinsing the prepared composite metal compound with a solution including manganese and drying the rinsed composite metal compound.
In the cathode active material for a secondary battery according to the present invention, the manganese oxide is present in the periphery of the primary particle, the manganese oxide forms a concentration gradient from a particle center to a particle surface in the secondary particle, and secondary battery including the cathode active material for a secondary battery according to the present invention has high safety, while exhibiting high capacity and high output.
The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Hereinafter, the present invention will be described in detail by the following embodiments. However, the following embodiments are merely illustrative and are not intended to limit the scope of the present invention. Any concept having substantially the same constitution and achieving the same operational effect as those of technical concept described in the claims of the present invention is included in the scope of the present invention.
A precursor represented by Ni0.98Co0.02(OH)2 was prepared by co-precipitation reaction. LiOH as a lithium compound and 1.4 mol of Al2O3 as an aluminum compound were added to the prepared precursor and heat-treated to prepare a cathode active material for a lithium secondary battery.
The prepared composite metal compound was rinsed with a washing solution containing 0.01 mol % of Mn and dried under the condition of 150° C. and 400 mmHg for 5 hours to prepare a cathode active material for a secondary battery represented by Li1.01Ni0.913CO0.07Al0.014Mn0.0001O2.
A cathode active material for a secondary battery represented by Chemical Formula of Li1.01Ni0.912C0.07Al0.014Mn0.0002O2 was prepared under the same conditions and by the same method as those of Inventive Example 1, except that the prepared composite metal compound was rinsed with a washing solution containing 0.02 mol % of Mn.
A cathode active material for a secondary battery represented by Chemical Formula of Li1.01Ni0.911Co0.07Al0.014Mn0.0003O2 was prepared under the same conditions and by the same method as those of Inventive Example 1, except that the prepared composite metal compound was rinsed with a washing solution containing 0.03 mol % of Mn.
A cathode active material for a secondary battery represented by Chemical Formula of Li1.01Ni0.911Co0.07Al0.014Mn0.0003O2 was prepared under the same conditions and by the same method as those of Inventive Example 1, except that the prepared composite metal compound was rinsed with a washing solution containing 0.04 mol % of Mn.
A cathode active material for a secondary battery represented by Chemical Formula of Li1.01Ni0.909Co0.07Al0.014Mn0.0005O2 was prepared under the same conditions and by the same method as those of Inventive Example 1, except that the prepared composite metal compound was rinsed with a washing solution containing 0.05 mol % of Mn.
A cathode active material for a secondary battery represented by Chemical Formula of Li1.01Ni0.908Co0.07Al0.014Mn0.0006O2 was prepared under the same conditions and by the same method as those of Inventive Example 1, except that the prepared composite metal compound was rinsed with a washing solution containing 0.06 mol % of Mn.
A lithium composite oxide represented by Chemical Formula Li1.01Ni0.914Co0.07Al0.014O2 was prepared under the same conditions and by the same method as those of Inventive Example 1, except that it was immersed in a manganese-containing solution for rinsing.
Concentrations of metals of the cathode active materials prepared in the above inventive examples were measured by an energy dispersive spectrometer (EDX) by varying measurement ratios and results thereof are illustrated in
In
Changes in the concentrations of manganese, cobalt, nickel, and aluminum of the cathode active material for a secondary battery of Inventive Example 4 were checked from the surface of the secondary particle to the center of the secondary particle on the basis of TEM measurement results, and results thereof are illustrated in
In
Weight percent (wt %) and atomic percent (at %) of manganese, cobalt, nickel, and aluminum in the TEM measurement range were measured and illustrated in Table 2 and
Changes in the concentrations of nickel, cobalt, aluminum and manganese included in the cathode active material for a secondary battery of Inventive Example 4 were measured on the surface of the secondary particle (surface, line data 2) and in a portion (grain boundary, line data 6) in contact with a boundary between the primary particles inside the secondary particle, and results thereof are illustrated in
In
As illustrated in
XRD measurement is made for the cathode active materials prepared in the above Inventive Examples and Comparative Example, and results thereof are illustrated in
In
In
A diffusion path of lithium ions according to respective positions of the primary particles of the cathode active material for a secondary battery of Inventive Example 4 was checked from TEM measurement data and is illustrated in
In
at the A position which is the surface position of the secondary particle and the C position which is the boundary between the primary particles in the secondary particle.
Residual lithium of the cathode active materials prepared in Inventive Examples 1 to 6 and the cathode active material prepared in Comparative Example were measured.
Specifically, 1 g of a lithium composite oxide was immersed in 5 g of distilled water and stirred for 5 minutes. After stirring, the lithium composite oxide was filtered to obtain a filtrate, to which 0.1 M of a HCl solution was added so as to be titrated to have pH 5. Here, the volume of the added HCl solution was measured to analyze residual lithium of the used cathode active material, and results thereof are illustrated in Table 3 below.
Batteries were manufactured using the secondary battery cathode active materials prepared according to Inventive Examples 1 to 6 and Comparative Example 1.
First, the secondary battery cathode active material, a super-P as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed at a weight ratio of 95:5:3 to prepare a slurry. The prepared slurry was uniformly applied to an aluminum foil having a thickness of 15 μm and vacuum-dried at 135° C. to prepare a cathode for a lithium secondary battery.
A coin battery was manufactured using the obtained cathode for a lithium secondary battery, a lithium foil as a counterpart electrode, a porous polyethylene film Celgard LLC., Celgard 2300) having a thickness of 25 μm as a separator, and a solvent including LiPF6 having a concentration of 1.15 M as a liquid electrolyte and including a mixture of ethylene carbonate and ethylmethylcarbonate mixed in a volume ratio of 3:7.
Initial capacities of the batteries respectively including the cathode active materials of the present invention and the cathode active material of comparative example manufactured in Manufacturing Example were measured, and results thereof are illustrated in
As illustrated in
Life characteristics of the coin batteries were measured at room temperature (25° C.) and high temperature (45° C.), and results thereof are illustrated in
As illustrated in
Charge//discharge characteristics when the coin batteries were charged/discharged one time or 50 times were measured at room temperature (25° C.) and a high temperature (45° C.), and results thereof were converted into dQ/dV to voltage (V) 12 and illustrated in
As illustrated in
After the coin batteries manufactured using the cathode active materials prepared in the Inventive Example and Comparative Example were charged/discharged 50 times, the coin batteries were disassembled, XRD Measurement was made on the obtained cathode active materials and compared with XRD data measured for the active materials before the batteries were manufactured. Results thereof are illustrated in
As illustrated in
In the case of a general battery, a crystal structure thereof deteriorates due to cation migration when the battery continues to be charged and discharged. As illustrated in
In the case of the cathode active material of the present invention, it can be seen that, the increase in the value of 4104) was merely 2.61% even after charging/discharging was continuously performed, which indicates that the extent of deterioration of the bulk structure even after charging/discharging was reduced.
XPS of the coin battery manufactured using the secondary battery cathode active material of Inventive Example 4 and XPS of the coil battery manufactured using the secondary battery cathode active material prepared in Comparative Example 1 in Manufacturing Example, before and after charging and discharging 50 times, were measured, and results thereof are illustrated in
In
The coin battery manufactured using the secondary battery cathode active material of Inventive Example 4 and the coin battery manufactured using the secondary battery cathode active material of Comparative Example 1 in Manufacturing Example were charged and discharged 50 times, cross-sections of the cathode active materials were measured by an EDX, and results thereof are illustrated in
As illustrated in
While the present invention has been illustrated and described in connection with the embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2017-0152449 | Nov 2017 | KR | national |
| 10-2017-0152450 | Nov 2017 | KR | national |
| 10-2017-0152451 | Nov 2017 | KR | national |
| 10-2018-0126427 | Oct 2018 | KR | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6040090 | Sunagawa et al. | Mar 2000 | A |
| 20110311869 | Oh | Dec 2011 | A1 |
| Number | Date | Country |
|---|---|---|
| 102017215146 | Feb 2019 | DE |
| 0 918 041 | Nov 2010 | EP |
| 3890185 | Mar 2007 | JP |
| 10-2005-0083869 | Feb 2005 | KR |
| 20160015779 | Feb 2016 | KR |
| Entry |
|---|
| English translation of DE-102017215146-A1 (Year: 2019). |
| English translation of KR-20160015779-A (Year: 2016). |
| Number | Date | Country | |
|---|---|---|---|
| 20190148725 A1 | May 2019 | US |
