A positive electrode material, a positive electrode sheet including the same, and a battery

Abstract

The application belongs to the technical field of batteries, and particularly relates to a positive electrode material, a positive electrode sheet comprising the positive electrode material and a battery. The positive electrode material provided by the application has good structural stability, and the battery comprising the positive electrode material has excellent cycle performance. The type and doping amount of the doping element A can be used to control the morphology of the positive electrode material in a directional manner, improve the compaction density of the positive electrode material, and thus improve the energy density of the positive electrode sheet. In addition, the A-O bond formed by the doping element A and the oxygen atoms in the crystal can improve the oxygen stability in the positive electrode material, so that the positive electrode material has a higher specific capacity and voltage platform.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a positive electrode material, a positive electrode sheet including the positive electrode material, and a battery. Background Technology

[0002] With the development and advancement of lithium-ion battery technology, increasingly higher demands are being placed on its capacity. In the composition of a lithium-ion battery, the capacity of the cathode material plays a crucial role. One important approach to improving lithium-ion battery capacity is to increase its charge and discharge voltage. However, as the voltage increases, the cathode material faces a series of adverse changes, including unstable crystal structure, rapid capacity decay, and a significant reduction in cycle performance. Therefore, developing a lithium-ion battery cathode material with high specific capacity, a high voltage plateau, good cycle performance, and interface stability at high voltages is a critical task. Summary of the Invention

[0003] To address the problems existing in the background art, the present invention provides a positive electrode material, a positive electrode sheet including the positive electrode material, and a battery. The positive electrode material belongs to the P63mc space group and has an O2 phase stacking structure. The positive electrode material exhibits high specific capacity, good interfacial stability, and cycle stability under high voltage. Using this positive electrode material can improve the specific capacity, cycle performance, rate performance, and energy density of the battery.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] A cathode material, wherein the cathode material is a lithium transition metal oxide comprising Co, A, and optionally M, wherein the A element is selected from at least one of B and P, and the M element is selected from at least one of Al, Mg, Ti, Mn, Te, Ni, W, Nb, Zr, La, and Y; the molar amount of A element per mole of cathode material is n. A The molar amount of Co in a unit mole of cathode material is n. Co The molar amount of element M in a unit mole of cathode material is n. M The n A and n Co+ n M The ratio is 0 <n A / n Co+ n M <0.05.

[0006] In some embodiments, the term can be optional or not.

[0007] In some embodiments, the n A and n Co+ n M0.002, 0.005, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.030, 0.032, 0.034, 0.035, 0.036, 0.038, 0.04, 0.042, 0.043, 0.045, 0.046, 0.048, or 0.049.

[0008] In some embodiments, the molar amount of the A element in a unit mole of the cathode material n A is 0 < n A <0.05, for example n A 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.030, 0.032, 0.034, 0.035, 0.036, 0.038, 0.04, 0.042, 0.043, 0.045, 0.046, 0.048, or 0.049.

[0009] In some embodiments, the molar amount of the M element in a unit mole of the cathode material n M is 0 ≤ n M <0.1, for example n M 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.030, 0.032, 0.034, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, or 0.095.

[0010] In some embodiments, the cathode material further comprises a Li element, and the molar amount of the Li element in a unit mole of the cathode material n Li is 0.7 < n Li <1, for example n Li 0.72, 0.75, 0.77, 0.78, 0.80, 0.82, 0.85, 0.86, 0.88, 0.89, 0.90, 0.92, 0.94, 0.95, 0.96, 0.98, or 0.99.

[0011] In some embodiments, the positive electrode material further comprises Na element, and the molar amount of Na element in unit mole of the positive electrode material is n Na 0 < n < 0.03 Na 0 < n < 0.03, for example, n Na 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026 or 0.028.

[0012] In some embodiments, the positive electrode material has a chemical formula of Li x Na y Co 1-a-b A a M b O2, 0.7 < x < 1, 0 < y < 0.03, 0 < a < 0.05, 0 ≤ b < 0.1, and 0 < a / 1-a < 0.05, wherein the definitions of A and M are as described above.

[0013] In some embodiments, the positive electrode material has an O2 phase stacking structure, and belongs to a P63mc space group.

[0014] In some embodiments, the positive electrode material has a polycrystalline morphology or has a single crystal morphology.

[0015] In some embodiments, the positive electrode material has a median particle size of 15 μm to 20 μm, for example, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm.

[0016] In some embodiments, the A element is selected from at least one of B and P, and is preferably B. The B element and the P element have a fluxing effect, so that the morphology of the positive electrode material is a single crystal or polycrystalline spherical morphology with a large particle size. In particular, the B element can make the structure of the positive electrode material more stable, and can stabilize the interface between the positive electrode material and the electrolyte during the charging and discharging process, which is beneficial to improve the cycle performance of the battery. At the same time, the B and P elements can significantly increase the gram capacity and the compaction density of the positive electrode material, which is beneficial to improve the gram capacity, the energy density and the rate performance of the battery.

[0017] In some embodiments, by controlling the type and doping amount of the A element, the morphology of the positive electrode material can be controlled. When the doping element A is a B element or B and P elements, the morphology of the positive electrode material is a single crystal morphology. When the doping element A is a P element, the morphology of the positive electrode material is a polycrystalline morphology.

[0018] In some embodiments, by controlling the kind and doping amount of the doping element A, the median particle size of the positive electrode material can be controlled to be 15-20 μm, the electrochemical kinetic performance and rate performance in the charge and discharge process can be improved, and the polarization phenomenon can be reduced, so that the battery has higher gram capacity, rate performance and cycle performance.

[0019] In some embodiments, the positive electrode material includes but is not limited to Li 0.92 Na 0.02 Co 0.958 B 0.03 Al 0.012 O2, Li 0.94 Na 0.018 Co 0.985 P 0.003 Al 0.012 O2, Li 0.96 Na 0.018 Co 0.95 B 0.02 P 0.004 Al 0.026 O2, Li 0.98 Na 0.018 Co 0.95 B 0.0 2P 0.004 Mg 0.015 O2.

[0020] The present application also provides a preparation method of the above positive electrode material, which comprises the following steps:

[0021] (1) a co-precipitate is prepared by using a co-precipitation method with a soluble Co salt and optionally a soluble salt containing an M element, and the co-precipitate is sintered to obtain a (Co 1-b M b )3O4 containing M element doping, wherein 0≤b<0.1;

[0022] (2) a mixture of (Co 1-b M b )3O4, a Na source and a compound containing an A element is sintered in an air atmosphere according to a stoichiometric ratio to prepare a Na m Co 1-a-b A a M b , wherein 0.7<m<1;

[0023] (3) the Na m Co 1-a-b A a M bMixing with the Li source according to the mass ratio of 1:(1.5-5), adding 10-40 times weight of deionized water, and performing ion exchange reaction at 100-200°C, washing and drying the reaction product after the reaction to obtain the positive electrode material.

[0024] Specifically, the specific steps of the co-precipitation reaction in step (1) include:

[0025] Mixing the soluble Co salt and the optional soluble salt containing M element according to the molar ratio of Co element and M element of (1-b):b, adding a solvent to obtain a mixed solution;

[0026] Adding a precipitant and a complexing agent to the mixed solution to obtain a reaction solution, adjusting the pH of the reaction solution to 6-8, and allowing the reaction solution to perform a co-precipitation reaction at a predetermined temperature and stirring rate to obtain a co-precipitate.

[0027] Further, in step (1), the soluble Co salt is one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate; and the soluble salt containing M element is one or more of nitrate, sulfate, chloride, and acetate containing M element;

[0028] Further, in step (1), the solvent for the co-precipitation reaction is one or more of deionized water, methanol, and ethanol;

[0029] Further, in step (1), the precipitant for the co-precipitation reaction is one or more of NaOH, KOH, Na2CO3, K2CO3, NaHCO3, and KHCO3. It should be noted that before adding the precipitant to the mixed solution, the precipitant can be pre-prepared to obtain a precipitant solution, and the solvent for preparing the precipitant solution can be one or more of deionized water, methanol, and ethanol;

[0030] Further, the molar concentration of the precipitant solution is 0.1-3 mol / L, and more preferably 1-3 mol / L;

[0031] Further, in step (1), the complexing agent for the co-precipitation reaction is one or more of ammonia, ammonium carbonate, and ammonium bicarbonate. It should be noted that before adding the complexing agent to the mixed solution, the complexing agent can be prepared to obtain a complexing agent solution, and the solvent for preparing the complexing agent solution can be one or more of deionized water, methanol, and ethanol;

[0032] Further, the molar concentration of the complexing agent solution is 0.1-3 mol / L, and more preferably 1-3 mol / L;

[0033] Further, in step (1), the temperature of the co-precipitation reaction is 25-85°C; and the time of the co-precipitation reaction is 24-36 h.

[0034] Further, in step (2), the Na source is one or more of Na2CO3, NaOH, Na2O, and NaCl.

[0035] Further, in step (2), the compound containing the element A is selected from one or more of B2O3, H3BO3, H2B4O7, HBO2, Na4P2O7, and Na3PO4.

[0036] Further, in step (2), (Co 1-b M b )3O4, the Na source, and the compound containing the element A are in a molar ratio of (0.7-1):(1-b-a):a, where 0

[0037] Further, in step (2), the sintering temperature is 750-950°C, more preferably 800-900°C, and the sintering time is 20-40h, more preferably 24-36h.

[0038] Further, in step (3), the Li source is one or more of LiOH, LiCl, and LiNO3.

[0039] It should be noted that the number of washing times and the washing agent used in step (3) are not particularly limited, and can be selected according to requirements, as long as the salt on the surface of the product can be removed, for example, the washing agent can be deionized water.

[0040] In the preparation process of the positive electrode material of the present application, by comprehensively adjusting the types of reactants, the parameters of coprecipitation reaction, the types and doping amounts of product elements, etc., the positive electrode material can have the specific chemical composition and structure described in the present application, and can greatly improve the specific capacity, cycle performance, rate performance, and energy density of lithium ion batteries.

[0041] The present application also provides a positive electrode sheet, which comprises the positive electrode material described above.

[0042] According to an embodiment of the present application, the positive electrode sheet comprises a current collector and a positive electrode active material layer; the positive electrode active material layer is arranged on at least one surface of the current collector; and the positive electrode active material layer comprises the positive electrode material described above.

[0043] According to an embodiment of the present application, the positive electrode active material layer further comprises a conductive agent and a binder.

[0044] According to an embodiment of the present application, the conductive agent includes but is not limited to carbon-based materials, metal-based materials, conductive polymers, or mixtures thereof.

[0045] According to an embodiment of the present application, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof.

[0046] According to an embodiment of the present application, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, silver.

[0047] According to an embodiment of the present application, the conductive polymer is a polyphenylene derivative.

[0048] According to an embodiment of the present application, the current collector includes, but is not limited to, aluminum foil, carbon-coated aluminum foil, perforated aluminum foil, stainless steel foil, polymer substrate coated with conductive metal, and any combination thereof.

[0049] According to an embodiment of the present application, the binder includes, but is not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), water-based acrylic resin, polyvinyl alcohol, polyvinyl butyral, polyurethane, fluorinated rubber, carboxymethyl cellulose (CMC), polyacrylic acid (PAA).

[0050] According to an embodiment of the present application, the positive electrode sheet can be prepared according to conventional methods in the art. Typically, the positive electrode material and optionally a conductive agent, a binder are dispersed in a solvent (e.g., NMP) to form a uniform positive electrode slurry, the positive electrode slurry is coated on a current collector, and after processes such as drying, a positive electrode sheet is obtained.

[0051] The present application also provides a battery comprising the positive electrode material described above, or a battery comprising the positive electrode sheet described above.

[0052] According to an embodiment of the present application, the charge cut-off voltage of the battery is greater than or equal to 4.5 V.

[0053] The present application has the following advantages:

[0054] (1) The positive electrode material provided by the present application has good structural stability, and the battery composed of the positive electrode material has excellent cycle performance.

[0055] (2) The positive electrode material provided by the present application, by the type and doping amount of the doping element A, on the one hand, can control the morphology of the positive electrode material in a targeted manner, improve the compaction density of the positive electrode material, and thus improve the energy density of the battery; on the other hand, the A-O bond formed by the doping element A and the oxygen atoms in the crystal can improve the oxygen stability in the positive electrode material, so that the positive electrode material has a higher specific capacity and voltage plateau. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 SEM image of the positive electrode material of Example 1.

[0057] Figure 2 SEM image of the cathode material in Example 4.

[0058] Figure 3 SEM image of the cathode material in Example 7.

[0059] Figure 4 SEM image of the cathode material in Comparative Example 1. Detailed Implementation

[0060] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0061] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0062] Example 1

[0063] (1) Cobalt sulfate and aluminum sulfate were mixed in a molar ratio of Co to Al of 0.97:0.03 and deionized water was added to obtain a mixed solution. Sodium hydroxide (a precipitant) and ammonia (a complexing agent) were added to the mixed solution to obtain a reaction solution. Ammonia was introduced to adjust the pH of the reaction solution to 7.5, and the reaction solution under stirring underwent a coprecipitation reaction to obtain a coprecipitate. The coprecipitate was sintered at 700℃ to obtain (Co... 0.97 Al 0.03 3O4 powder;

[0064] (2) According to the stoichiometric ratio, (Co) 0.97 Al 0.03 A mixture of Na₂O₄, Na₂CO₃, and H₃BO₃ was mixed at a molar ratio of Na, Co, and B of 0.72:0.955:0.015 to obtain a powder. This powder was then sintered at 900°C for 36 hours in air to obtain Na₂O₄. 0.72 Co 0.955 B 0.015 Al 0.03 O2;

[0065] (3) Put Na 0.72 Co 0.955 B 0.015 Al 0.03 O2 and LiOH were mixed at a mass ratio of 1:2.5, and 20 times their weight of deionized water were added. An ion exchange reaction was carried out at 120°C. After the reaction was complete, the reaction product was washed and dried to obtain the cathode material Li.0.9 Na 0.02 Co 0.955 B 0.015 Al 0.03 O2.

[0066] Example 2

[0067] (1) The same as Example 1;

[0068] (2) A mixture of (Co 0.97 Al 0.03 )3O4, Na2CO3 and H3BO3 was mixed according to the molar ratio of Na, Co, B being 0.74:0.95:0.02, to obtain a mixture powder, and the mixture powder was sintered at 900°C for 36h under air atmosphere to obtain Na 0.74 Co 0.95 B 0.02 Al 0.03 O2.

[0069] (3) Na 0.74 Co 0.95 B 0.02 Al 0.03 O2 was mixed with LiOH according to the mass ratio of 1:2.5, and 20 times weight of deionized water was added, and ion exchange reaction was carried out at 120°C, and after the reaction was completed, the reaction product was washed and dried to obtain the positive electrode material Li 0.93 Na 0.015 Co 0.95 B 0.02 Al 0.03 O2.

[0070] Example 3

[0071] (1) The same as Example 1;

[0072] (2) A mixture of (Co 0.97 Al 0.03 )3O4, Na2CO3 and H3BO3 was mixed according to the molar ratio of Na, Co, B being 0.76:0.945:0.025, to obtain a mixture powder, and the mixture powder was sintered at 900°C for 36h under air atmosphere to obtain Na 0.76 Co 0.945 B 0.025 Al 0.03 O2.

[0073] (3) Na 0.76 Co 0.945 Al 0.03 B 0.025O2 is mixed with LiOH in a mass ratio of 1:2.5, 20 times weight of deionized water is added, and ion exchange reaction is carried out at 120°C. After the reaction is completed, the reaction product is washed and dried to obtain the positive material Li 0.93 Na 0.015 Co 0.945 B 0.025 Al 0.03 O2.

[0074] Example 4

[0075] (1) Cobalt sulfate and aluminum sulfate are mixed in a molar ratio of Co element to Mg element of 0.97:0.015, and deionized water is added to obtain a mixed solution. Sodium hydroxide as a precipitant and ammonia water as a complexing agent are added to the mixed solution to obtain a reaction solution. Ammonia water is introduced to adjust the pH value of the reaction solution to 7.5. The reaction solution is allowed to carry out a co-precipitation reaction under stirring to obtain a co-precipitate. The co-precipitate is sintered at 700°C to obtain (Co 0.97 Mg 0.015 )3O4 powder;

[0076] (2) The mixture of (Co 0.97 Mg 0.015 )3O4, NaOH and Na4P2O7 is mixed in a molar ratio of Na, Co and P of 0.72:0.983:0.002 to obtain a mixture powder. The mixture powder is sintered at 900°C for 36h in an air atmosphere to obtain Na 0.72 Co 0.983 P 0.002 Mg 0.015 O2.

[0077] (3) Na 0.72 Co 0.983 P 0.002 Mg 0.015 O2 is mixed with LiCl in a mass ratio of 1:2.5, 20 times weight of deionized water is added, and ion exchange reaction is carried out at 120°C. After the reaction is completed, the reaction product is washed and dried to obtain the positive material Li 0.91 Na 0.018 Co 0.983 P 0.002 Mg 0.015 O2.

[0078] Example 5

[0079] (1) The same as Example 4;

[0080] (2) The same as Example 4; 0.97 Mg 0.015)3O4, NaCl and Na4P2O7 mixture is mixed according to the molar ratio of Na, Co, P as 0.74:0.9825:0.0025, to obtain the mixture powder, the mixture powder is sintered at 900°C for 36h under air atmosphere, to obtain Na 0.74 Co 0.9825 P 0.0025 Mg 0.015 O2.

[0081] (3) Na 0.74 Co 0.9825 P 0.0025 Mg 0.015 O2 is mixed with LiCl according to the mass ratio of 1:2.5, and 20 times weight of deionized water is added, ion exchange reaction is carried out at 120°C, after the reaction is completed, the reaction product is washed and dried to obtain the positive material Li 0.94 Na 0.016 Co 0.9825 P 0.0025 Mg 0.015 O2.

[0082] Example 6

[0083] (1) same as example 4;

[0084] (2) (Co 0.97 Mg 0.015 )3O4, NaCl and Na4P2O7 mixture is mixed according to the molar ratio of Na, Co, P as 0.76:0.982:0.003, to obtain the mixture powder, the mixture powder is sintered at 900°C for 36h under air atmosphere, to obtain Na 0.76 Co 0.982 P 0.003 Mg 0.015 O2.

[0085] (3) Na 0.76 Co 0.982 P 0.003 Mg 0.015 O2 is mixed with LiCl according to the mass ratio of 1:2.5, and 20 times weight of deionized water is added, ion exchange reaction is carried out at 120°C, after the reaction is completed, the reaction product is washed and dried to obtain the positive material Li 0.96 Na 0.014 Co 0.982 P 0.003 Mg 0.015 O2.

[0086] Example 7

[0087] (1) mixed cobalt sulfate and aluminum sulfate according to the molar ratio of Co element and Al element of 0.97:0.02, and added deionized water to obtain a mixed solution; added a precipitant sodium hydroxide and a complexing agent ammonia water into the mixed solution to obtain a reaction solution, adjusted the pH value of the reaction solution to 7.5 by passing in ammonia water, and allowed the reaction solution to perform a co-precipitation reaction under stirring to obtain a co-precipitate; sintered the co-precipitate at 700°C to obtain (Co 0.97 Al 0.02 )3O4 powder;

[0088] (2) mixed (Co 0.97 Al 0.02 )3O4, NaCl, H3BO3, Na4P2O7 according to the molar ratio of Na, Co, B, P of 0.72:0.955:0.022:0.003 to obtain a mixture powder, sintered the mixture powder at 900°C for 36h under an air atmosphere to obtain Na 0.72 Co 0.955 B 0.022 P 0.003 Al 0.02 O2;

[0089] (3) mixed Na 0.72 Co 0.955 B 0.022 P 0.003 Al 0.02 O2 with a Li source (the weight ratio of LiOH and LiNO3 is 8:2) according to the mass ratio of 1:2.5, and added 20 times weight of deionized water, and performed an ion exchange reaction at 120°C, washed and dried the reaction product after the reaction to obtain a positive electrode material Li 0.92 Na 0.02 Co 0.955 B 0.022 P 0.003 Al 0.02 O2.

[0090] Example 8

[0091] (1) same as example 7;

[0092] (2) mixed (Co 0.97 Al 0.02 )3O4, NaCl, H3BO3, Na4P2O7 according to the molar ratio of Na, Co, B, P of 0.74:0.945:0.032:0.003 to obtain a mixture powder, sintered the mixture powder at 900°C for 36h under an air atmosphere to obtain Na 0.74 Co 0.945 B 0.032 P0.003 Al 0.02 O2;

[0093] (3) Na 0.74 Co 0.945 B 0.032 P 0.003 Al 0.02 O2 was mixed with Li source (LiOH and LiNO3 in weight ratio of 8:2) in mass ratio of 1:2.5, and 20 times weight of deionized water was added, ion exchange reaction was carried out at 120℃, after the reaction was completed, the reaction product was washed and dried to obtain the positive material Li 0.94 Na 0.018 Co 0.945 B 0.032 P 0.003 Al 0.02 O2.

[0094] Example 9

[0095] (1) same as example 7;

[0096] (2) (Co 0.97 Al 0.02 )3O4, NaCl, H3BO3, Na4P2O7 mixture was mixed in the molar ratio of Na, Co, B, P of 0.76:0.935:0.04:0.005 to obtain the mixed powder, the mixed powder was sintered at 900℃ for 36h in air atmosphere to obtain Na 0.76 Co 0.935 B 0.04 P 0.005 Al 0.02 O2;

[0097] (3) Na 0.76 Co 0.935 B 0.04 P 0.005 Al 0.02 O2 was mixed with Li source (LiOH and LiNO3 in weight ratio of 8:2) in mass ratio of 1:2.5, and 20 times weight of deionized water was added, ion exchange reaction was carried out at 120℃, after the reaction was completed, the reaction product was washed and dried to obtain the positive material Li 0.96 Na 0.016 Co 0.935 B 0.04 P 0.005 Al 0.02 O2.

[0098] Comparative example 1

[0099] (1) same as example 1;

[0100] (2) The mixture of (Co 0.97 Al 0.03 )304, Na2CO3 is mixed according to the molar ratio of Na:Co = 0.72:0.97, to obtain the mixture powder, and the mixture powder is sintered at 900°C for 36h under air atmosphere to obtain Na 0.72 Co 0.97 Al 0.03 O2.

[0101] (3) The Na 0.72 Co 0.97 Al 0.03 O2 is mixed with LiOH according to the mass ratio of 1:2.5, and 20 times the weight of deionized water is added to carry out ion exchange reaction at 120°C. After the reaction is completed, the reaction product is washed and dried to obtain the positive electrode material Li 0.9 Na 0.02 Co 0.97 Al 0.03 O2.

[0102] Comparative Example 2

[0103] (1) The same as Example 4;

[0104] (2) The mixture of (Co 0.97 Mg 0.015 )304, Na2CO3 is mixed according to the molar ratio of Na:Co = 0.72:0.985, to obtain the mixture powder, and the mixture powder is sintered at 900°C for 36h under air atmosphere to obtain Na 0.72 Co 0.985 Mg 0.015 O2.

[0105] (3) The Na 0.72 Co 0.985 Mg 0.015 O2 is mixed with LiOH according to the mass ratio of 1:2.5, and 20 times the weight of deionized water is added to carry out ion exchange reaction at 120°C. After the reaction is completed, the reaction product is washed and dried to obtain the positive electrode material Li 0.91 Na 0.018 Co 0.985 Mg 0.015 O2.

[0106] Comparative Example 3

[0107] (1) The same as Example 7;

[0108] (2) The mixture of (Co 0.97 Al 0.02)3O4, Na2CO3, H3BO3, Na4P2O7 mixture was mixed according to the molar ratio of Na, Co, B, P was 0.72:0.91:0.05:0.02, the mixture powder was obtained, the mixture powder was sintered at 900℃ for 36h under air atmosphere, Na 0.72 Co 0.91 B 0.05 P 0.02 Al 0.02 O2;

[0109] (3) Na 0.72 Co 0.91 B 0.05 P 0.02 Al 0.02 O2 and LiOH were mixed according to the mass ratio of 1:2.5, and 20 times of deionized water was added, and ion exchange reaction was carried out at 120℃, and after the reaction was completed, the reaction product was washed and dried to obtain the positive material Li 0.92 Na 0.02 Co 0.91 B 0.05 P 0.02 Al 0.02 O2.

[0110] The positive material prepared in the above examples belongs to P63mc space group, and has O2 phase stacking structure.

[0111] The above examples and comparative examples all use CR2032 type button cell to study the electrochemical performance of the positive material, and the preparation method of the button cell is as follows:

[0112] The positive sheet uses NMP as the solvent, and the positive active material (the positive material prepared in the examples and comparative examples), the conductive agent Super P, and the binder polyvinylidene fluoride PVDF are mixed according to the mass ratio of 97:1.5:1.5, and are stirred uniformly in a defoaming machine to prepare a slurry positive material with a solid content of 70%, and the positive material is uniformly coated on the surface of an aluminum foil, and is baked in a vacuum oven at 100℃ for 12h, and then is rolled, cut, and obtained.

[0113] The positive sheet and the lithium sheet negative electrode, PP / PE / PP three-layer separator, and 1mol / L LiPF6 / (EC+DEC) electrolyte (volume ratio 1:1) are assembled into a button cell for electrochemical test in a glove box.

[0114] The performance test process of the button cell prepared above is as follows:

[0115] The test temperature is 25℃, and the voltage interval is 3.0-4.5V. The first 5 cycles are used for rate performance test. During charging, 0.1C constant current charging is performed until the voltage is 4.5V. During discharging, 0.1C, 0.2C, 0.5C, 1C and 2C rates are used for discharging at 4.5V constant voltage. Then, 50 cycles are used for cycle performance test under the condition of 0.5C charging and discharging rate and 3.0-4.55V voltage interval. The capacity retention rate (%) of lithium ion battery after 50 cycles = the discharge capacity of the 55th cycle / the discharge capacity of the 6th cycle x 100%.

[0116] Table 1: Performance test results of positive electrode materials and button cells of examples and comparative examples

[0117]

[0118] From the data in Table 1, it can be seen that Comparative Example 1-2 only dopes M elements such as Al and Mg. The capacity, rate performance and cycle performance of Comparative Example 1-2 are all worse than those of Examples 1-9 at high voltage (≥4.5V), which indicates that the doping of B and P can improve the specific capacity, rate performance and cycle stability of the positive electrode material. Among them, the co-doping of B and P has the best effect, which indicates that B and P have a synergistic effect. However, the doping amount of B and P cannot be too much, otherwise the capacity, rate performance and cycle performance of the positive electrode material will be greatly reduced. This is because too much A element will cause the structure of the positive electrode material to be unstable, resulting in excessive irreversible capacity and decreased cycle performance.

[0119] From the electron microscope images of Example 1, Example 4, Example 7 and Comparative Example 1, it can be seen that the positive electrode material containing B doping has a single crystal morphology, and the positive electrode material without B element has a polycrystalline morphology. This indicates that the fluxing effect of B element has a great influence on the morphology of the material during sintering. After changing from polycrystalline morphology to single crystal morphology, the compaction density of the material also increases, thereby improving the energy density of the lithium ion battery.

[0120] The above describes the embodiments of the present application. However, the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A positive electrode material, the positive electrode material being a lithium transition metal oxide comprising Co element, Li element, A element, Na element and M element, the A element being a combination of B and P, the M element being selected from at least one of Al, Ti, Mn, Te, Ni, W, Nb, Zr, La and Y or at least one of Mg, Ti, Mn, Te, Ni, W, Nb, Zr, La and Y; The molar amount of the A element in the unit mole of the positive electrode material is n A The molar amount of the Co element in the unit mole of the positive electrode material is n Co The molar amount of the M element in the unit mole of the positive electrode material is n M The n A The n Co+ The ratio of n M / n A / n Co+ n M <0.05; n: molar amount of the A element in one mole of the positive electrode material A 0 < n A <0.05; n: molar amount of the M element in one mole of the positive electrode material M 0 < n M <0.1; n is the molar amount of Na element in one mole of the positive electrode material Na 0 < n Na <0.03; n is the molar amount of Li element in one mole of the positive electrode material Li 0.7 < n Li <1; The chemical formula of the positive electrode material is: Li x Na y Co 1-a-b A a M b O2, 0.7 < x < 1, 0 < y < 0.03, 0 < a < 0.05, 0 < b < 0.1, and 0 < a / 1-a < 0.05; the positive electrode material having a polycrystalline morphology or having a single crystal morphology; the positive electrode material having an O2 phase stacking structure belonging to a P63mc space group.

2. The cathode material of claim 1, wherein, the positive electrode material having a median particle size of 15 μm to 20 μm.

3. The cathode material of claim 1 or 2, wherein, The chemical formula of the positive electrode material is: Li 0.96 Na 0.016 Co 0.935 B 0.04 P 0.005 Al 0.02 O2. 4.A positive electrode sheet, the positive electrode sheet comprising the positive electrode material according to any one of claims 1 to 3. 5.A battery, the battery comprising the positive electrode material according to any one of claims 1 to 3 or the battery comprising the positive electrode sheet according to claim 4.

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