Patent Application
20170077496
1. Field of the Invention
The present invention generally relates to a metal gradient-doped cathode material for lithium batteries, a method for preparing same, and more specifically to a cathode material comprising a modifying metal formed of at least one of magnesium (Mg), calcium (Ca), strontium (Sr), boron (B), aluminum (Al), gallium (Ga), indium (In), titanium (Ti), silicon (Si) and tin (Sn) in a gradient of concentration so as to improve the capacity, cycle-life and safety of lithium battery.
2. The Prior Arts
Recently, as the problem of global warming and the energy crisis of petroleum decrease become more serious, people have made many efforts to develop electric vehicles with more energy saving, carbon reducing and environmental protection. To meet environmental protection and energy saving, one of the best driving power sources for the electric vehicles is the high energy-density lithium battery with more safety. Many advanced countries around the world like America, Europe, Japan, Korea, China and Taiwan have aggressively spent various resources in researching and developing related technology for more powerful electric vehicles and lithium batteries for mass production. Additionally, the industry of 3C consumer electronic products made much progress, and smart phones and tablet PC have become more popular and almost a must-have for everybody to carry around and perform some mobile and smart functions like wireless on-line surfing, video playing and cloud information receiving. As a result, it is crucial to prolong the running time of the power source for the 3C electronic products, and thus needs to develop higher energy-density batteries to meet the requirement of electric vehicles and 3C products. The above properties of the lithium battery are strongly related to the active materials of electrodes, especially the cathode material.
Since the cathode material greatly influences the performance of the lithium battery, not only low cost, high capacity, long cycle-life and large charge/discharge current are necessary, but also thermal stability, thereby improving operation safety for the battery. Among current cathode materials, the hexagonal-crystalline material draws more attention because of higher energy-density. Lithium cobalt oxide (LiCoO2) is one of the most commonly-used cathode materials. However, Co is a strategic material, costly, hard available and toxic. Such that another material, lithium nickel oxide (LiNiO2), with high energy-density, low cost and less toxic has been studied to replace LiCoO2. Currently, LiNiO2 still has some troublesome problems like difficult synthesis, poor thermal-stability and unstable lattice structure. To overcome these issues, part of Ni in LiNiO2 is replaced by Co, and the stability of lattice structure is enhanced. Such a hexagonal-crystalline cathode material, LiNixCo1-xO2, exhibits higher capacity (larger than 180 mAh g−1) and better thermal-stability than LiNiO2, and becomes one of the most crucial materials for the next generation of the lithium battery. While this cathode material has many advantages, some low-cost cathode materials like LiNixCoyMn1-x-yO2 have been progressively developed. The LiNixCoyMn1-x-yO2 cathode material has lower capacity than the LiNixCo1-xO2 cathode material, but its material cost, cyclability and safety can be further improved by adding Mn.
Currently, there are two approaches to develop high energy-density cathode material. One approach is focused on the Ni-rich material to increase its capacity. The other is to increase working-voltage like larger than 4.2 V so as to increase its capacity.
While the cathode material with the hexagonal-crystalline structure has higher capacity and is widely used in the lithium battery, however, it easily reacts with the electrolyte on the surface of powder, leading to short cycle-life and poor safety.
In the prior arts, many researchers tried to enhance stability of the hexagonal-crystalline cathode material for lithium battery by adding some more stable modifying materials. Such the modifying materials are different from the active metals like Ni, Co and Mn in the hexagonal-crystalline body.
Specifically, two modifying processes are more commonly used, including surface coating and metal doping.
As for the surface coating method, the cathode material is basically coated with a nano-layer of non-electrochemical active material to reduce the reactivity with the electrolyte, thereby prolong the cycle-life of battery. However, it is still difficult and uneasy for current technology to uniformly coat a nanometer protective layer on the surface of cathode material. As a result, industrial utility is greatly reduced.
The metal doping method employs some non-electrochemical active metal to uniformly dope into the crystal structure of cathode material so as to enhance the stability of material. However, more amount of the modifying metal is needed to effectively suppress the reactivity of the cathode material with the electrolyte, and the original advantage of high capacity is thus reduced.
Therefore, it is greatly needed to provide a metal gradient-doped cathode material for lithium batteries, in which a less-amount modifying metal is used to improve the stability of material, so as to manufacture lithium batteries with high capacity, good cyclability and high-safety, thereby overcoming the above problems in the prior arts.
The primary objective of the present invention is to provide a metal gradient-doped cathode material for lithium batteries. The cathode material of the present invention is basically a powder particle without any boundary or layered structure and the powder generally comprises a hexagonal-crystalline material body and a modifying metal doped in the hexagonal-crystalline material body. In particular, the modifying metal is doped in a gradient of concentration. Specifically, the metal gradient-doped cathode material is expressed by a chemical formula “f mol % M doped LizNiaCobMncO2”, where LizNiaCobMncO2 represents the hexagonal-crystalline material body, M represents the modifying metal, which has a molar content f larger than 0.5% and smaller than 10% of the sum of molar content of Ni (nickel), Co (cobalt) and Mn (manganese) in the hexagonal-crystalline material body, specified by 0.5% (a+b+c)≦f≦10% (a+b+c).
The hexagonal-crystalline material body, LizNiaCobMncO2, as an active component of cathode material comprises a lithium metal oxide of a single metal selected from Ni and Co, or two metals selected from Ni/Co, Ni/Mn and Co/Mn, or three metals comprising Ni, Co and Mn, where z, a, b and c in the chemical formula are specified by 0.9≦z≦1.2, a+b+c=1, 0≦a≦1, 0≦b≦1 and 0≦c≦0.6. The modifying metal is a metal or a metalloid selected from at least one of magnesium (Mg), calcium (Ca), strontium (Sr), boron (B), aluminum (Al), gallium (Ga), indium (In), titanium (Ti), silicon (Si) and tin (Sn). Especially, the modifying metal is more concentrated on the surface of the powder and gradually decreases toward the core of the powder so as to form a gradient profile of concentration. The concentration of modifying metal on the surface of the powder, is expressed as f′, the concentration of the modifying metal at the core of the powder, is expressed as f″, and the concentration ranges of modifying metal are f′>f>f″>0 and f′−f″>0.2% (a+b+c). The surface of the powder with more the modifying metal can effectively reduce the reactivity of the cathode material with the electrolyte in the lithium battery. As a result, the cyclability and safety for the lithium battery is greatly improved. In particular, less amount of the modifying metal is enough to achieve the desired effect so as to avoid the traditional problem that more amount of the modifying metal greatly reduces the capacity of the battery, thereby increasing the energy-density and cycle-life of the lithium battery. The metal gradient-doped cathode material is formed by coating modifying metal hydroxide on the surface of the hexagonal-crystalline material by a chemical co-precipitation method, and then sintering the modifying metal hydroxide coated hexagonal-crystalline material.
More specifically, the cathode material of the present invention exhibits not only the aspect that the reactivity of the cathode material with the electrolyte is effectively reduced by adding less amount of the modifying metal, but also the advantage that electrochemical performance and thermal stability are improved and the overall efficiency, cycle-life and industrial utility of the battery are increased.
The present invention will be apparent to those skilled in the art by reading the following detailed description of a preferred embodiment thereof, with reference to the attached drawings, in which:
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
Please refer to
The hexagonal-crystalline material body of the metal gradient-doped cathode material comprises a lithium metal oxide of a single metal selected from Ni and Co, or two metals selected from Ni/Co, Ni/Mn and Co/Mn, or three metals comprising Ni, Co and Mn, where z, a, b and c in the chemical formula LizNiaCobMncO2 are specified by 0.9≦z≦1.2, a+b+c=1, 0≦a≦1, 0≦b≦1 and 0≦c≦0.6. More specifically, the hexagonal-crystalline material body is doped with the modifying metal, which is configured in a continuously variation of concentration. In particular, the modifying metal is different from the active metal like Ni, Co and Mn, and exhibits weaker reactivity with the electrolyte used in lithium batteries.
It is preferred that the modifying metal comprises a metal or a metalloid selected from at least one of magnesium (Mg), calcium (Ca), strontium (Sr), boron (B), aluminum (Al), gallium (Ga), indium (In), titanium (Ti), silicon (Si) and tin (Sn). In particular, the modifying metal is more concentrated on the surface A and continuously decreases toward the core B in a direction indicated by C, and a gradient of concentration is thus formed. The concentration of modifying metal on the surface A of the powder, is expressed as f′, the concentration of the modifying metal at the core B of the powder, is expressed as f″, and the concentration ranges of modifying metal are f′>f>f″>0 and f′−f″>0.2% (a+b+c).
The metal gradient-doped cathode material is formed by coating modifying metal hydroxide on the surface of the hexagonal-crystalline material by a chemical co-precipitation method, and then sintering the modifying metal hydroxide coated hexagonal-crystalline material.
In addition, the metal gradient-doped cathode material of the present invention is a R-3m space group. The D50 particle size of powder is 0.5˜25 μm. For instance, the concentration of the modifying metal varieties around the region of, a half of the D50 particle size of powder, that is, from 0.25 to 12.5 μm. The metal gradient-doped cathode material has a tap density larger than 1.5 g cm 3, and its specific surface area is 0.1˜25 m2 g−1.
Some illustrative examples as preferred embodiments and comparative examples will be described in detail for physical and electrochemical properties to more clearly demonstrate the effects implemented by the present invention.
1. Synthesis of the lithium nickel cobalt oxide cathode material gradient-doped with aluminum as the modifying metal: A chemical co-precipitation method is used to synthesize spherical nickel cobalt hydroxide (N0.82Co0.18(OH)2). An aqueous solution of 1.2 M NiSO4 and CoSO4 (molar ratio of Ni:Co 4:1) is pumped into a tank reactor (capacity, 2 L) with continuous stirring. Simultaneously, a 2.0 M NaOH solution and an 8.0 M NH4OH solution, which is used as a chelating agent, are fed separately into the reactor. The concentration of NH4OH, pH and temperature are maintained at 1.2 M, 10.5 and 60° C., respectively. After vigorous stirring for 20 hours, spherical Ni0.82Co0.18(OH)2 precipitations with particle diameters of approximately 10˜15 μm are formed. Then, lithium hydroxide (LiOH.H2O) is added and mixed, where a molar ratio of lithium salt to nickel/cobalt metal is 1.02:1.00. The mixture is sintered at 750° C. in an oxygen atmosphere for 10 hours so as to obtain the LiNi0.82Co0.18O2 cathode material. The as-synthesized LiNi0.82Co0.18O2 powders are suspended in a 0.3 M NH4OH solution, and then an appropriate amount of Al2(SO4)3 solution is slowly added into the suspension with continuous stirring for 2 hours. Simultaneously, a 3.0 M NH4OH solution is fed into the reactor. In order to control the relative supersaturation, the pH and temperature are adjusted to 8.0 and 60° C., respectively. A certain amount of aluminum hydroxide(Al(OH)3) is uniformly coated on the surface of LiNi0.82Co0.18O2 by a chemical co-precipitation method and then sintered at 750° C. in an oxygen atmosphere for 3 hours. Thus, the cathode material of lithium nickel cobalt oxide doped with a gradient of aluminum metal indicated by Al(GD)-LNCO is obtained.
2. Manufacturing and measuring the coin cell: Appropriate amounts of active material, graphite/carbon black and PVdF(polyvinylidene fluoride) are prepared according to a weight ratio of 90:6:4, and then NMP is added and mixed to form a uniform slurry. A 150 μm doctor blade is used to spread the slurry on an 18 μm aluminum foil. The coated film as the electrode plate is dried on a hot plate and then further dried in vacuum to remove NMP solvent. Before assembling the coin cell, the electrode plate is roll-pressed and punched to form a circular disk (12 mm) In the coin cell, a disk of lithium metal serves as the anode, and an Al(GD)-LNCO electrode-plate is the cathode. The electrolyte is prepared by mixing 1.0 M LiPF6 dissolved in EC(ethylene carbonate) and DMC(dimethyl carbonate) solvent at a volume ratio of 1:1. The polyethylene membrane as a separator is soaked in the electrolyte for 24 hours prior to use. The charge/discharge ranges are 2.8˜4.3 V and 2.8˜4.5 V, respectively, and the charge/discharge currents are 0.1 C˜7 C so as to measure various electrochemical properties of the Al(GD)-LNCO cathode material.
3. DSC (differential scanning calorimeter) for the Al(GD)-LNCO cathode material: The coin cell is assembled and charged to 4.3 V. The cell is then dissembled in an argon-filled dry box to take out the cathode electrode, and 3mg of the cathode material is scraped from the cathode plate and placed into an aluminum pan. 3 μL of the electrolyte is added and then the aluminum pan is sealed. DSC scanning is carried out at a scan rate of 5° C. min−1 from 180˜280° C.
As compared with the cathode material manufactured in the illustrative example 1, the comparative example 1 manufactures the lithium nickel cobalt oxide cathode material without any modification, indicated by LNCO. Specifically, LNCO is synthesized via the following steps: spherical nickel cobalt hydroxide, (Ni0.82Co0.18(OH)2), is formed by a chemical co-precipitation method; lithium hydroxide is added and mixed at a molar ratio of lithium salt to nickel/cobalt metal being 1.02:1.00; and then the mixture is sintered at 750° C. in an oxygen atmosphere for 13 hours so as to obtain the LiNi0.82Co0.18O2 cathode material (LNCO). The process of manufacturing the coin cell is the same as that of Al(GD)-LNCO. The LNCO cathode material is also measured by DSC.
The measurement results of the illustrative example 1 and the comparative example 1 are illustrated in
As for analysis of the physical properties, inductively coupled plasma/optical emission spectrometer (ICP/OES) and scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS) are used to measure the quantitative element analysis for the bulk, surface and cross section of the Al(GD)-LNCO cathode material of the illustrative example 1. For example, the average molar percentage of aluminum element doped in lithium nickel cobalt oxide is 2.55% measured by ICP/OES.
For analysis of electrochemical properties, the differences between the Al(GD)-LNCO cathode material in illustrative example 1 and the LNCO cathode material in the comparative example 1 are clearly shown in
Moreover,
Refer to
Form the above mentioned, the Al(GD)-LNCO cathode material of the illustrative example 1 is better than the LNCO cathode material of the comparative example 1 in terms of electrochemical properties.
Further refer to
1. Synthesis of the lithium nickel cobalt manganese oxide cathode material gradient-doped with magnesium as the modifying metal: An aqueous solution of 1.2 M NiSO4, CoSO4 and MnSO4 (molar ratio of Ni:Co:Mn≈5:2:3) is pumped into a tank reactor (capacity, 2 L) with continuous stirring. Simultaneously, a 2.0 M NaOH solution and an 8.0 M NH4OH solution, which is used as a chelating agent, are fed separately into the reactor. The concentration of NH4OH, pH and temperature are maintained at 1.2 M, 10.5 and 60° C., respectively. After vigorous stirring for 20 hours, spherical Ni0.51Co0.20Mn0.29(OH)2 precipitations with particle diameters of approximately 10˜15 μm are formed. After spherical nickel cobalt manganese hydroxide (Ni0.51Co0.20Mn0.29(OH)2) is synthesized by a chemical co-precipitation method, a sintering process is performed at 600° C. in an oxygen atmosphere for 10 hours to obtain the spherical nickel cobalt manganese oxide, and then lithium hydroxide (LiOH.H2O) is added and mixed at a molar ratio of lithium salt to nickel/cobalt/manganese metal being 1.02:1.00. The mixture is sintered at 850° C. in an oxygen atmosphere for 18 hours to obtain the LiNi0.51Co0.20Mn0.29O2 cathode material. The as-synthesized LiNi0.51Co0.20Mn0.29O2 powders are suspended in a 1.0 M NH4OH solution, and then an appropriate amount of MgSO4 solution is slowly added into the suspension with continuous stirring for 1 hour. Simultaneously, a 0.5 M NaOH solution and a 6.5 M NH4OH solution are fed separately into the reactor. In order to control the relative supersaturation, the pH and temperature are adjusted to 11.0 and 60° C., respectively. A certain amount of magnesium hydroxide(Mg(OH)2) is uniformly coated on the surface of LiNi0.51Co0.20Mn0.29O2 by a chemical co-precipitation method and then sintered at 850° C. in an oxygen atmosphere for 2 hours so as to obtain the cathode material of lithium nickel cobalt manganese oxide doped with a gradient of magnesium metal indicated by Mg(GD)-LNCMO.
2. Manufacturing and measuring the coin cell: Appropriate amounts of active material, graphite/carbon black, and PVdF (polyvinylidene fluoride) are prepared according to a weight ratio of 91:6:3, and then NMP is added and mixed to form a uniform slurry. A 150 μm doctor blade is used to spread the slurry on an 18 μm aluminum foil. The coated film as the electrode plate is dried on a hot plate and then further dried in vacuum to remove NMP solvent. Before assembling the coin cell, the electrode plate is roll-pressed and punched to form a circular disk (12 mm). In the coin cell, a disk of lithium metal serves as the anode, and a Mg(GD)-LNCMO electrode-plate is the cathode. The electrolyte is prepared by mixing 1.0 M LiPF6 dissolved in EC and DMC solvent at a volume ratio of 1:1. The polyethylene membrane as a separator is soaked in the electrolyte for 24 hours prior to use. The charge/discharge ranges are 2.8˜4.3 V and 2.8˜4.5 V, respectively, and the charge/discharge currents are 0.1 C˜7 C so as to measure various electrochemical properties of the Mg(GD)-LNCMO cathode material.
3. DSC (differential scanning calorimeter) for the Mg(GD)-LNCMO cathode material: The coin cell is assembled and charged to 4.5 V. The cell is then dissembled in an argon-filled dry box to take out the cathode electrode, and 3 mg of the cathode material is scraped from the cathode plate and placed into an aluminum pan. 3 μL of the electrolyte is added and then the aluminum pan is sealed. DSC scanning was carried out at a scan rate of 5° C. min−1 from 220˜300° C.
As compared with the cathode material manufactured in the illustrative example 2, the comparative example 2 manufactures the lithium nickel cobalt manganese oxide cathode material without any modification, indicated by LNCMO. Specifically, LNCMO is synthesized via the following steps: spherical nickel cobalt manganese hydroxide, (Ni0.51Co0.20Mn0.29(OH)2), is formed by a chemical co-precipitation method; spherical nickel cobalt manganese hydroxide is sintered at 600° C. in an oxygen atmosphere for 10 hours to obtain the spherical nickel cobalt manganese oxide; lithium hydroxide is added and mixed at a molar ratio of lithium salt to nickel/cobalt/manganese metal being 1.02:1.00; and then the mixture is sintered at 850° C. in an oxygen atmosphere for 20 hours so as to obtain the LiNi0.51Co0.20Mn0.29O2 cathode material (LNCMO). The subsequent process of manufacturing the coin cell is the same as that of Mg(GD)-LNCMO. The LNCMO cathode material is also measured by DSC.
The measurement results of the illustrative example 2 and the comparative example 2 are illustrated in
As for analysis of the physical properties, ICP/OES and SEM with EDS are used to measure the quantitative element analysis for the bulk, surface and cross section of the Mg(GD)-LNCMO cathode material of the illustrative example 2. The average molar percentage of magnesium element doped in lithium nickel cobalt manganese oxide is 1.7% measured by ICP/OES.
For analysis of electrochemical properties, the differences between the Mg(GD)-LNCMO cathode material in illustrative example 2 and the LNCMO cathode material in the comparative example 2 are clearly shown in
Further refer to
Form the above mentioned, the Mg(GD)-LNCMO cathode material of the illustrative example 2 is better than the LNCMO cathode material of the comparative example 2 in terms of electrochemical properties.
Also, refer to
More specifically, the secondary lithium battery using the cathode material of the present invention may comprise a shell formed of stainless steel, aluminum or aluminum alloy with a shape of circular, rectangular or cylinder. The present invention also applicable to polymer lithium batteries packaged by aluminum foil thermal sealing or other packaging types so as to increase the safety of operation and performances of battery.
From the above mention, one primary feature of the present invention is that the metal gradient-doped hexagonal-crystalline cathode material employs the modifying metal more concentrated on the surface of the cathode powder to reduce the reactivity with the electrolyte, and the modifying metal is specifically configured to gradually decrease toward the core to reduce the doping amount of the modifying metal such that both high capacity and long cycle-life at higher working voltage are implemented, and the industrial utility of the high energy-density cathode material is greatly improved. As a result, the cathode material of the present invention is very applicable to the cathode of the lithium battery.
Although the present invention has been described with reference to the preferred embodiments thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.
