TWI487175B - Lithium nickel manganese oxide composite material, method for making the same, and lithium battery using the same - Google Patents

Description

Lithium nickel manganese oxide composite material, preparation method thereof and lithium ion battery

The invention relates to a lithium nickel manganese oxide composite material and a preparation method thereof, and a lithium ion battery.

The surface of the particle of the positive electrode active material of the lithium ion battery is coated with other materials, which is a common method for modifying the positive electrode active material in the prior art. For example, coating a layer of carbon on the surface of the lithium iron phosphate particles can effectively solve the problem of low conductivity of lithium iron phosphate, and the lithium iron phosphate coated with the carbon layer has good conductivity. In addition, prior art has shown that coating aluminum phosphate on the surface of lithium cobaltate or other positive active material particles can improve the thermal stability of the positive electrode of a lithium ion battery (see the literature "Correlation between AlPO ₄ nanoparticle coating thickness on LiCoO ₂ cathode and thermal Stablility" J. Cho, Electrochimica Acta 48 (2003) 2807-2811 and U.S. Patent No. 7,326,498.

In the prior art, the method of coating the positive electrode active material with aluminum phosphate is to first prepare a dispersion formed by dispersing aluminum phosphate particles in water, and adding the positive electrode active material particles to the dispersion of the prepared aluminum phosphate particles, and adsorbing The action is to adsorb the aluminum phosphate particles on the surface of the large particles of the positive electrode active material, and then evaporate the water in the dispersion liquid, and Heat treatment at 700 ° C to form a positive electrode active material having aluminum phosphate particles on its surface.

However, since aluminum phosphate is insoluble in water, aluminum phosphate particles may form agglomeration when dispersed in water, and when a large amount of positive electrode active material is added to the aluminum phosphate dispersion, the positive electrode active material added first adsorbs a large amount of aluminum phosphate particles, and then added. The positive electrode active material particles may not adsorb enough aluminum phosphate particles. Referring to FIG. 9, even if it can be well coated, the above method determines that the product 20 is microscopically distributed in the form of small particles 22 on the surface of the large active material 24, not a layer of uniform aluminum phosphate. Therefore, the aluminum phosphate coating layer formed on the surface of the positive electrode active material by the above method is not uniform enough, and it is impossible to ensure that the surface of each positive electrode active material can be uniformly coated with aluminum phosphate, thereby circulating the lithium ion battery to which the positive electrode active material is applied. Poor performance makes this method difficult for large-scale industrial applications.

In view of the above, there is provided a method capable of forming a uniform aluminum phosphate coating layer on a surface of a lithium nickel manganese oxide particle, and a lithium nickel manganese oxide composite material having the aluminum phosphate coating layer, and the application of the lithium nickel manganese oxide Composite lithium ion batteries are necessary.

A lithium nickel manganese oxide composite material comprising positive electrode active material particles and an aluminum phosphate layer coated on a surface of the positive electrode active material particles, the positive electrode active material particles being of the chemical formula Li _x Ni _0.5+ya Mn _1.5-yb M _a N _b O ₄ represents, wherein 0.1≦x≦1.1, 0≦y<1.5, 0≦ay<0.5, and 0≦b+y<1.5, M and N are alkali metal elements, alkaline earth metal elements, group 13 elements, One or more of a Group 14 element, a transition group element, and a rare earth element.

A method for preparing a lithium nickel manganese oxide composite material, comprising: providing an aluminum nitrate solution; adding a positive electrode active material particle to be coated to the aluminum nitrate solution to form a mixture, wherein the material of the positive electrode active material particle is a chemical formula _a N _b O ₄ represents, wherein 0.1≦x≦1.1, 0≦y<1.5, 0≦ay<0.5, and 0≦b+y<1.5, M and N are alkali metal elements, alkaline earth metal elements, group 13 elements, One or more of a group 14 element, a transition group element, and a rare earth element; adding a phosphate solution to the mixture to form a reaction, forming an aluminum phosphate layer on the surface of the positive electrode active material particle; and heat treating the positive electrode having an aluminum phosphate layer on the surface Active material particles.

A lithium ion battery comprising a positive electrode comprising the above lithium nickel manganese oxide composite material.

Compared with the prior art, the invention avoids the uneven adsorption caused by solid-solid mixing, resulting in uneven coating of aluminum phosphate, and is suitable for large-scale industrial applications. Further, the present invention can form a uniform thickness and continuous aluminum phosphate layer on the surface of the positive electrode active material particles, instead of depositing the aluminum phosphate particles on the surface of the positive electrode active material particles, thereby having better electrochemical performance.

10‧‧‧ positive composite particles

12‧‧‧ positive active material particles

14‧‧‧Aluminum phosphate layer

20‧‧‧ products

22‧‧‧Small particles

24‧‧‧ Large particles

1 is a schematic view showing the structure of an active material of a phosphoric acid-coated positive electrode according to an embodiment of the present invention.

2 is a scanning electron micrograph of an aluminum phosphate coated lithium cobaltate according to an embodiment of the present invention.

3 is a transmission electron micrograph of an aluminum phosphate coated lithium cobaltate according to an embodiment of the present invention.

4 is a cycle performance test curve of aluminum phosphate coated lithium cobalt oxide according to an embodiment of the present invention.

5 is a cycle performance test curve of aluminum phosphate coated lithium nickelate and lithium niobate uncoated in a comparative experiment according to an embodiment of the present invention.

Figure 6 is a scanning electron micrograph of a high magnification aluminum phosphate coated lithium cobaltate in a comparative experiment.

Figure 7 is a scanning electron micrograph of a low-amplification aluminum phosphate coated lithium cobaltate in a comparative experiment. .

Fig. 8 is a graph showing the cycle performance test of the aluminum phosphate-coated positive electrode active material of the comparative experiment.

Fig. 9 is a schematic view showing the structure of a prior art aluminum phosphate-coated positive electrode active material.

The lithium nickel manganese oxide composite material provided by the present invention, a preparation method thereof, and a lithium ion battery will be further described in detail below with reference to the accompanying drawings and specific embodiments.

Referring to FIG. 1, an embodiment of the present invention provides a positive electrode composite material particle 10 comprising a positive electrode active material particle 12 and an aluminum phosphate layer 14 coated on the surface of the positive electrode active material particle. The mass percentage of the aluminum phosphate layer 14 in the positive electrode composite material particles 10 is from 0.1% to 3%. The thickness of the aluminum phosphate layer 14 is preferably from 5 nm to 20 nm. The aluminum phosphate layer 14 is formed in situ on the surface of the positive electrode active material particle 12. The aluminum phosphate layer 14 is a layer of aluminophosphate material having a uniform thickness and continuous thickness. All surfaces of the positive electrode active material particles 12 are covered by the continuous aluminum phosphate layer 14. Further, an interface diffusion may be formed at the interface between the aluminum phosphate layer 14 and the positive electrode active material particle 12 to diffuse cobalt atoms into the aluminum phosphate layer 14.

The material of the positive electrode active material particles 12 may be a layered lithium cobaltate structure or a nickel-doped spinel lithium manganate structure, specifically, a chemical formula of Li _x Co _1-z M _z O ₂ or Li _x Ni _0.5+ya Mn _1.5-yb M _a N _b O ₄ represents, where 0.1≦x≦1.1, 0≦y<1.5, 0≦ay<0.5, and 0≦b+y<1.5, and 0≦z<1. M and N are each selected from one or more of an alkali metal element, an alkaline earth metal element, a Group 13 element, a Group 14 element, a transition group element, and a rare earth element. Preferably, M and N are selected from the group consisting of Cr, Co, and V. At least one of Ti, Al, Fe, Ga, and Mg. Wherein the range of y is preferably 0 ≦ y < 0.1. Specifically, the material of the material of the positive electrode active material particle 12 may have a chemical formula of LiCoO ₂ or LiNi _0.5 Mn _1.5 O ₄ . The particle diameter of the positive electrode active material particles 12 is preferably from 100 nm to 100 μm, more preferably from 1 μm to 20 μm.

An embodiment of the present invention provides a method for forming a positive electrode active material of a lithium ion battery with a lithium phosphate coating, which comprises the steps of: step one, providing an aluminum nitrate solution; and step two, to be coated The positive electrode active material particles are added to the aluminum nitrate solution to form a mixture; in step 3, a phosphate solution is added to the mixture to react to form an aluminum phosphate layer on the surface of the positive electrode active material particle; and in step 4, the surface is heat treated with aluminum phosphate The positive electrode active material particles of the layer were obtained as positive electrode composite particles.

The material of the positive electrode active material particles is the above-mentioned layered lithium cobaltate structure or nickel-doped spinel lithium manganate structure. The aluminum nitrate solution includes a liquid phase solvent and aluminum nitrate dissolved in the solvent. It is understood that the solvent is selected to be a solvent which can dissociate aluminum nitrate to form Al ³⁺ . Therefore, the solvent is not limited to water, and may be a volatile organic solvent. Preferably, the solvent is a mixture of one or more of ethanol, acetone, dichloroethane and chloroform. The use of water as a solvent and an organic solvent such as ethanol as a solvent can prevent the positive electrode active material particles from reacting with water to lower the performance of the positive electrode active material.

In the above step two, the positive electrode active material particles are insoluble in the aluminum nitrate solution, and the two are solid-liquid mixed, and the purpose is to uniformly adhere a layer of Al ³⁺ on the surface of the positive electrode active material particles. Since Al ³⁺ is present in an ionic form, it can be uniformly attached to the surface of the positive electrode active material particle, and the positive electrode active material particle forms an atomic coating. Further, the amount of the positive active material to be added may be controlled, and the ratio of the positive electrode active material particles to the aluminum nitrate solution may be controlled so that the aluminum nitrate solution can cover the surface of the positive electrode active material particles, so that the obtained mixture is in a slurry state. . The purpose of forming the slurry mixture is mainly to control the addition amount of the aluminum nitrate solution just enough to form an aluminum phosphate coating layer on the surface of the positive electrode active material particles. Specifically, the volume ratio of the volume of the aluminum nitrate solution to the positive electrode active material particles is about 1:10 to 1:40. The particle diameter of the positive electrode active material particles is preferably less than 20 μm. The amount of the aluminum nitrate solution added can be determined by the mass percentage of the aluminum phosphate coating layer to be formed in the positive electrode composite material particles. Preferably, the mass percentage of the aluminum phosphate coating layer in the positive electrode composite material particles is 0.1%. To 3%.

In the above step three, the phosphate solution includes water as a solvent, and a soluble phosphate such as an ammonium phosphate dissolved in the solvent. The ammonium phosphate salt comprises one or more of ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), and triammonium phosphate ((NH ₄ ) ₃ PO ₄ ). the mix of. The phosphate solution contains phosphate ions. The phosphate ion may be a mixture of one or more of orthophosphate ion (PO ₄ ^3- ), dihydrogen phosphate ion (H ₂ PO ₄ ^- ), and monohydrogen phosphate ion (HPO ₄ ^2- ). When the phosphate solution is added to the slurry mixture, the phosphate ions react with Al ³⁺ attached to the surface of the positive electrode active material particles to form a uniform aluminum phosphate precipitate in situ on the surface of the positive electrode active material particles. Preferably, the phosphate solution may be added dropwise to the slurry mixture and stirred so that the phosphate ion and the Al ³⁺ can be uniformly reacted on the surface of the positive electrode active material particle. Similar to the aluminum nitrate solution, the amount of the phosphate solution added can be determined by the mass percentage of the positive electrode composite particles to be formed by the aluminum phosphate coating layer to be formed.

In the above step four, the purpose of the heat treatment is to make the aluminum phosphate and the positive active material Better bonding at the interface to form a composite and remove residual solvent and ammonium nitrate formed by the reaction. By this heat treatment, interface diffusion may be formed at the interface between the aluminum phosphate and the positive electrode active material, and metal atoms in the positive electrode active material may be diffused into the aluminum phosphate layer. The heat treatment temperature may be from 400 ° C to 800 ° C. The heat treatment time is preferably from 0.5 to 2 hours.

Since the method first adds the positive electrode active material particles to the aluminum nitrate solution, and then adds a phosphate solution which can react with aluminum ions to form aluminum phosphate in the aluminum nitrate solution, thereby forming a continuous layer in situ on the surface of the positive electrode active material particles. Aluminum phosphate layer. Since the liquid phase aluminum nitrate solution is mixed with the solid phase positive electrode active material particles, the aluminum ions can be uniformly coated on the surface of the positive electrode active material particles, and therefore, the aluminum phosphate precipitate formed by the aluminum ions after the in situ reaction is also It can be coated more uniformly and continuously on the entire surface of the positive electrode active particles. Compared with the method of first synthesizing aluminum phosphate particles and adsorbing the aluminum phosphate particles to the surface of the positive electrode active material particles by adsorption, the method avoids uneven adsorption due to solid-solid mixing, resulting in uneven coating of aluminum phosphate, Continuous or incomplete coating, suitable for large-scale industrial applications. In addition, the method can form a complete uniform and continuous aluminum phosphate layer on the surface of the positive electrode active material particles instead of depositing the aluminum phosphate particles on the surface of the positive electrode active material particles. The aluminum phosphate layer can pass ions while insulating electron migration between the electrolyte and the active material, thereby preventing the electrolyte from decomposing at a higher voltage while completing the insertion and extraction of lithium ions, thereby making the cathode active. The material can have better battery electrochemical performance and capacity retention performance at higher voltages.

In the embodiment of the present invention, the positive electrode composite material particles are prepared by coating the positive electrode active material particles with aluminum phosphate by using the above method, and the positive electrode composite material particles are used in a lithium ion battery for performance test.

Example 1

In the present embodiment, the positive electrode active material particles are lithium cobaltate particles, and the chemical formula is LiCoO ₂ . The lithium aluminum phosphate-lithium cobalt composite material includes lithium cobaltate particles and an aluminum phosphate layer coated on the surface of the lithium cobaltate particles.

In the preparation of the lithium aluminum phosphate-cobaltate composite, the aluminum nitrate solution is a solution of aluminum nitrate in ethanol. The aluminum nitrate solution had a volume of 30 ml and a molar concentration of 0.16 mol/liter. The lithium cobaltate particles were added in an amount of 100 g. The phosphate solution was an aqueous solution of (NH ₄ ) ₂ HPO ₄ . Three kinds of aluminum phosphate-cobaltate composite particle samples were prepared under the conditions of heat treatment temperature of 400 ° C, 500 ° C and 600 ° C respectively, and the aluminum phosphate layer accounted for 1% by mass of the total mass. Further, a lithium aluminum phosphate-cobaltate composite sample was prepared under the conditions of a heat treatment temperature of 600 ° C and a mass percentage of the total mass of the aluminum phosphate layer of 1.5%. Referring to FIG. 2 and FIG. 3, in the obtained sample, the aluminum phosphate layer is uniformly coated on the surface of the lithium cobaltate particles, and the aluminum phosphate is uniformly observed by high-rate transmission electron microscopy. The form covers the surface of the surface of the lithium cobaltate particles. These four kinds of samples were used as positive electrode active materials, and a certain proportion of conductive agent and binder were mixed and uniformly applied to the surface of the positive electrode current collector to form a positive electrode, and a lithium metal plate was used as a negative electrode, and the positive electrode and the negative electrode were separated through a separator. The electrolyte is infiltrated and assembled into a lithium ion battery for charge and discharge performance testing.

The positive electrode active material particles coated with aluminum phosphate improve the surface structure of the positive electrode active material particles due to the coating aluminum phosphate, provide a platform for the lithium ions to be deflated, and at the same time act as a barrier layer, effectively suppressing the four The valence cobalt ion reacts with the electrolyte to stabilize the lithium cobaltate structure and improve the electrochemical cycle performance. Referring to FIG. 4, the above four kinds of samples were subjected to a constant current charge and discharge cycle test at a current of 0.5 C. The cutoff voltage of the charge was 4.5 V, and the cutoff voltage of the discharge was 2.7 V. Can be found from the figure, adopted The sample prepared by the method of the invention can uniformly coat the aluminum cobaltate particles, and can still have a high capacity and a stable capacity retention rate when charged at a higher voltage, and the capacity retention rate after 50 cycles is More than 90%, the specific capacity is 160 mAh / g to 175 mAh / g. Also, as the heat treatment temperature is increased, the capacity of the battery is increased. The change in the percentage of aluminum phosphate has little effect on battery capacity.

Example 2

In the present embodiment, the positive electrode active material particles are spinel-type lithium nickel manganese oxide particles having a chemical formula of LiNi _0.5 Mn _1.5 O ₄ . The aluminum phosphate-lithium nickel manganese oxide composite material comprises lithium nickel manganese oxide particles and an aluminum phosphate layer coated on the surface of the lithium nickel manganese oxide particles.

The preparation method of the aluminum phosphate-lithium nickel manganese oxide composite material is the same as the preparation method of the aluminum phosphate-lithium cobaltate composite material particles of the above-mentioned Embodiment 1, and the heat treatment temperature is selected to be 600 ° C, which is different only in the material of the positive electrode active material particles. For lithium nickel manganese oxide, the aluminum phosphate layer accounts for 0.5% by mass of the total mass. This aluminum phosphate-lithium nickel manganese oxide composite material was used as a positive electrode active material, and assembled into a lithium ion battery under the same conditions as in Example 1. The lithium ion battery was subjected to a constant current charge and discharge cycle test at a current of 0.2 C. The cutoff voltage of the charge was 5 V, and the cutoff voltage of the discharge was 3 V. After 50 cycles, the capacity retention rate of the battery was above 95%, and the specific capacity was It is about 138 mAh/g. In addition, referring to FIG. 5, the lithium ion battery is subjected to a constant current charge and discharge cycle test at a current of 1 C. After 50 cycles of 1 C current, the capacity retention rate of the battery can still reach 95%, and the specific capacity is about 132 mAh/g. .

Comparative experiment 1

For comparison with the positive electrode composite particles prepared in Example 1 of the present invention, another comparative sample was prepared by the prior art method by mixing an aqueous solution of (NH ₄ ) ₂ HPO _{4 with} an aqueous solution of aluminum nitrate to form phosphoric acid in water. Aluminum particles forming a dispersion; introducing lithium cobaltate particles into the dispersion, adsorbing aluminum phosphate particles on the surface of the lithium cobaltate particles by adsorption; and heat treating the cobalt acid adsorbed on the surface with aluminum phosphate particles at 600 ° C Lithium particles were obtained to obtain the comparative sample. Referring to FIG. 6 and FIG. 7, in the comparative sample prepared by the prior art method, the morphology of the aluminum phosphate particles is aggregated on the surface of the lithium cobaltate particles, and the aluminum phosphate particles are agglomerated to make the coating uneven.

This comparative sample was used as a positive electrode active material, and a battery was assembled under the same conditions as in Example 1 to carry out a charge and discharge performance test. Further, lithium cobalt oxide particles not coated with any material were used as a positive electrode active material, and assembled into a lithium ion battery under the same conditions as in Example 1, and subjected to charge and discharge performance tests. The above Example 1 differs from the comparative experiment only in the positive electrode active material, and other battery conditions and test conditions are the same.

Referring to FIG. 8, the cycle capacity of the comparative sample and the uncoated lithium cobaltate particle sample decreased sharply, and the capacity retention rate after 50 cycles was less than 85%, mainly due to uneven coating of lithium cobaltate particles. Or uncoated, such that when charging is performed under high pressure, lithium cobaltate reacts with the electrolyte to lower the capacity of the battery.

Comparative experiment 2

The uncoated lithium nickelate particles were used as a positive electrode active material, and assembled into a lithium ion battery under the same conditions as in Example 1, and subjected to charge and discharge performance tests. The test results were compared with the test results of Example 2 in FIG. 5, and it was found that the lithium ion battery using the uncoated lithium nickelate particles as the positive electrode active material was charged after 50 cycles at 1 C current. The capacity retention of the cell is approximately 86% and the specific capacity is approximately 118 mAh/g.

In summary, the present invention has indeed met the requirements of the invention patent, and has filed a patent application according to law. However, the above description is only a preferred embodiment of the present invention, and it is not possible to limit the scope of the patent application of the present invention. Equivalent modifications or variations made by those skilled in the art in light of the spirit of the invention are intended to be included within the scope of the following claims.

10‧‧‧ positive composite particles

12‧‧‧ positive active material particles

14‧‧‧Aluminum phosphate layer

Claims (6)

A method for preparing a lithium nickel manganese oxide composite material, comprising: providing an aluminum nitrate solution; adding a positive electrode active material particle to be coated to the aluminum nitrate solution to form a mixture, wherein the positive electrode The material of the active material particles is represented by the chemical formula Li _x Ni _0.5+ya Mn _1.5-yb M _a N _b O ₄ , where 0.1≦x≦1.1, 0≦y<1.5, 0≦ay<0.5, and 0≦b+ y<1.5, M and N are one or a plurality of alkali metal elements, alkaline earth metal elements, Group 13 elements, Group 14 elements, transition group elements and rare earth elements; adding a phosphate solution to the mixture for reaction, The surface of the positive electrode active material particles forms an aluminum phosphate layer; and the positive electrode active material particles having the aluminum phosphate layer on the surface are heat-treated. The method for producing a lithium nickel manganese oxide composite according to the above item 1, wherein the step of adding the positive electrode active material particles to be coated to the aluminum nitrate solution further controls the positive active material. The amount is added to make the mixture mud-like. The method for producing a lithium nickel manganese oxide composite according to claim 1, wherein the aluminum nitrate solution comprises a solvent and aluminum nitrate dissolved in the solvent, and the solvent is ethanol. The method for preparing a lithium nickel manganese oxide composite according to claim 1, wherein the phosphate solution comprises water and an ammonium phosphate salt dissolved in water, and the ammonium phosphate salt comprises ammonium dihydrogen phosphate and hydrogen phosphate. Mixing one or more of ammonium and triammonium phosphate. The method for producing a lithium nickel manganese oxide composite according to claim 1, wherein the heat treatment temperature is from 400 ° C to 600 ° C. The method for producing a lithium nickel manganese oxide composite according to claim 1, wherein a volume ratio of the volume of the aluminum nitrate solution to the positive electrode active material particles is 1:10 to 1:40.