Cathode material, preparation method and application thereof

Abstract

This application relates to a cathode material, a preparation method thereof and an application. The preparation method of the cathode material includes: mixing a Li source, a flux and a nickel-cobalt-manganese precursor to obtain a mixed raw material; performing high-temperature calcination on the mixed raw material at gradually decreasing temperatures in multiple stages to obtain a pre-product, the temperature of the high-temperature calcination being 900°C to 1050°C; performing low-temperature calcination on the pre-product, the low-temperature calcination temperature being 650°C to 920°C; the molar ratio n of Li atoms in the Li source to the nickel-cobalt-manganese precursor being 0.5 < n < 1.15; the flux including an inorganic salt MX, where M includes Li + , Na + , K + , Rb + , Cs + , Mg 2+ , Ca 2+ , Sr 2+ and Ba 2+ and at least one of them, and X includes F ‑ , Cl ‑ , Br ‑ , I ‑ , NO3 ‑ and SO4 2‑ and at least one of them. This preparation method can reduce the content of the Li source while reducing the agglomeration of product particles and the generation of grain boundaries.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] The grain boundary existing in the positive electrode material is one of the main factors for capacity retention degradation. Due to uneven stress at the grain boundary interface caused by charging and discharging, the grain boundary cracking occurs in the electrochemical cycle process, thereby increasing the interface side reaction, increasing the impedance, and causing part of the active material to be deactivated. The amount of grain boundary in the positive electrode material prepared by the traditional solid phase method is relatively large; and in the molten salt method, the inorganic molten salt and the Li source can modify the microstructure of the positive electrode material, reduce the agglomeration of the product particles, and reduce the generation of grain boundaries.

[0003] The traditional preparation method of the positive electrode material with reduced Li source content can reduce the adhesion and corrosion of the positive electrode material to the saggar to save costs, but after reducing the content of the Li source, the particle size of the product is reduced, and a large amount of agglomerates and grain boundaries are generated. SUMMARY

[0004] Therefore, it is necessary to provide a positive electrode material and a preparation method and application thereof. The preparation method of the positive electrode material can reduce the agglomeration of the product particles and the generation of grain boundaries while reducing the content of the Li source.

[0005] In a first aspect, the present application provides a preparation method of a positive electrode material, comprising:

[0006] mixing a Li source, a fluxing agent and a nickel-cobalt-manganese precursor to obtain a mixed raw material;

[0007] performing high-temperature calcination on the mixed raw material in multiple stages with the temperature gradually reduced in each stage to obtain a pre-product, wherein the temperature of the high-temperature calcination is 900-1050℃;

[0008] performing low-temperature calcination on the pre-product, wherein the temperature of the low-temperature calcination is 650-920℃;

[0009] the molar ratio n of Li atoms in the Li source to the nickel-cobalt-manganese precursor is 0.5

[0010] the fluxing agent comprises an inorganic salt MX, wherein M comprises at least one of Li + , Na + , K + , Rb + , Cs + , Mg 2+ , Ca 2+ , Sr 2+ and Ba 2+ , and X comprises F - , Cl- Br - I - NO3 - and SO4 2- .

[0011] In some embodiments, the high-temperature calcination is performed for 2.1h-26h; and / or, the low-temperature calcination is performed for 3h-10h.

[0012] In some embodiments, the Li source comprises one or more of LiOH, LiOH·H2O, Li2CO3, LiNO3, and CH3COOLi.

[0013] In some embodiments, the nickel-cobalt-manganese precursor comprises Ni x Co y Mn z (OH)2, wherein x+y+z=1, 0.6≤x≤1, 0≤y≤0.4, 0≤z≤0.4.

[0014] In some embodiments, the molar ratio m of the fluxing agent to the nickel-cobalt-manganese precursor is 0.001

[0015] In one of the embodiments, the mixed raw materials are subjected to two-stage high-temperature calcination with temperature gradually decreasing in stages, the first-stage high-temperature calcination is performed at a temperature of 980℃-1050℃ for a constant temperature time of 0.1h-2h, and the second-stage high-temperature calcination is performed at a temperature of 900℃-980℃ for a time of 2-24h.

[0016] In one of the embodiments, the high-temperature calcination is performed at a temperature increasing rate of 3℃ / min-6℃ / min.

[0017] and / or, the pre-product is subjected to low-temperature calcination and then cooled to below 200℃ at a cooling rate of 2℃ / min-10℃ / min.

[0018] In a second aspect, the present application provides a positive electrode material prepared by any of the above-mentioned preparation methods.

[0019] In a third aspect, the present application provides a positive electrode sheet comprising a current collector and an active layer on at least one surface of the current collector, wherein the active layer comprises the positive electrode material prepared by any of the above-mentioned preparation methods or the above-mentioned positive electrode material.

[0020] In a fourth aspect, the present application provides a lithium ion battery comprising the above-mentioned positive electrode sheet.

[0021] The preparation method of the positive electrode material reduces the content of Li source in the preparation of the positive electrode material by the molten salt method. In order to reduce the generation of agglomerates and grain boundaries, the mixed raw materials are first calcined in a relatively high temperature range of the high temperature calcination, at which the particle size of the positive electrode material can be rapidly increased. Then, the positive electrode material is calcined in a relatively low temperature range of the high temperature calcination or calcined for multiple times with the temperature gradually decreasing, so as to repair the internal structure of the positive electrode material and reduce the lithium-nickel mixing. By this method, the positive electrode material with low grain boundaries and few agglomerates can be prepared by the molten salt method after reducing the content of Li source, and the positive electrode material has good electrochemical performance. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The SEM image of the positive electrode material provided for Example 1 of the present application;

[0023] Figure 2 The SEM image of the positive electrode material provided for Example 2 of the present application;

[0024] Figure 3 The SEM image of the positive electrode material provided for Example 3 of the present application;

[0025] Figure 4 The SEM image of the positive electrode material provided for Example 4 of the present application;

[0026] Figure 5 The SEM image of the positive electrode material provided for Example 5 of the present application;

[0027] Figure 6 The SEM image of the positive electrode material provided for Example 6 of the present application;

[0028] Figure 7 The SEM image of the positive electrode material provided for Comparative Example 1 of the present application;

[0029] Figure 8 The SEM image of the positive electrode material provided for Comparative Example 2 of the present application;

[0030] Figure 9 The SEM image of the positive electrode material provided for Comparative Example 3 of the present application;

[0031] Figure 10 The SEM image of the positive electrode material provided for Comparative Example 4 of the present application. DETAILED DESCRIPTION

[0032] In order to make the above objectives, features and advantages of the present application more apparent, the specific embodiments of the present application will be described in detail below with the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in many different ways from what is described herein, and should not be construed as being limited to the embodiments set forth herein below, but should be given the widest scope in accordance therewith.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0034] An embodiment of the present application provides a preparation method of a positive electrode material, comprising:

[0035] mixing a Li source, a fluxing agent and a nickel-cobalt-manganese precursor to obtain mixed raw materials;

[0036] performing high-temperature calcination on the mixed raw materials in multiple stages with temperature gradually decreasing in each stage to obtain a pre-product, wherein the high-temperature calcination is performed at a temperature of 900-1050℃;

[0037] performing low-temperature calcination on the pre-product, wherein the low-temperature calcination is performed at a temperature of 650-920℃;

[0038] a molar ratio n of Li atoms in the Li source to the nickel-cobalt-manganese precursor is 0.5

[0039] the fluxing agent comprises an inorganic salt MX, wherein M comprises at least one of Li + , Na + , K + , Rb + , Cs + , Mg 2+ , Ca 2+ , Sr 2+ and Ba 2+ , and X comprises at least one of F - , Cl - , Br - , I - , NO3 - and SO4 2- .

[0040] The preparation method of the positive electrode material reduces the content of the Li source in the preparation of the positive electrode material by the molten salt method. In order to reduce the generation of agglomerates and grain boundaries, the mixed raw materials are first calcined in a relatively high temperature range of the high-temperature calcination, at which the particle size of the positive electrode material can be rapidly increased. Then, the first calcination or the calcination with gradually reduced temperature is performed in a relatively low temperature range of the high-temperature calcination, so as to repair the internal structure of the positive electrode material and reduce the lithium-nickel mixing. By this method, the positive electrode material with low grain boundaries and few agglomerates can be prepared when the content of the Li source is reduced by the molten salt method, and the positive electrode material has good electrochemical performance.

[0041] Optionally, the temperature of the high-temperature calcination is 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, 960℃, 970℃, 980℃, 990℃, 1000℃, 1010℃, 1020℃, 1030℃, 1040℃ or 1050℃. When the temperature of the high-temperature calcination is too low, the particle size of the pre-product obtained is small, which is easy to agglomerate and lead to more crystallization, and large agglomerates are formed in the subsequent calcination, thereby reducing the electrochemical performance of the positive electrode material. When the temperature of the high-temperature calcination is too high, the internal structure of the positive electrode material changes, and more lithium-nickel mixing occurs in the positive electrode material, thereby reducing the electrochemical efficiency of the positive electrode material.

[0042] Optionally, the temperature of the low-temperature calcination is 650℃, 680℃, 700℃, 720℃, 740℃, 750℃, 780℃, 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃ or 920℃.

[0043] Optionally, the molar ratio n of the Li atoms in the Li source to the nickel-cobalt-manganese precursor is 0.50001, 0.5001, 0.501, 0.51, 0.52, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.12, 1.14, 1.149, 1.1499 or 1.14999.

[0044] In some embodiments, the time of the high-temperature calcination is 2.1-26h. Optionally, the time of the high-temperature calcination is 2.1h, 2.2h, 2.3h, 2.5h, 3h, 4h, 5h, 6h, 8h, 10h, 12h, 15h, 17h, 20h, 22h, 24h or 26h.

[0045] In some embodiments, the time of the low-temperature calcination is 3h-10h. Optionally, the time of the low-temperature calcination is 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h.

[0046] In some embodiments, the high-temperature calcination is performed for 2.1-26 hours, and the low-temperature calcination is performed for 3-10 hours.

[0047] In one of the embodiments, the high-temperature calcination is performed in an oxygen atmosphere.

[0048] In one of the embodiments, the low-temperature calcination is performed in an oxygen atmosphere.

[0049] In some embodiments, the Li source comprises one or more of LiOH, LiOH H2O, Li2CO3, LiNO3, and CH3COOLi.

[0050] In some embodiments, the nickel-cobalt-manganese precursor comprises Ni x Co y Mn z (OH)2, wherein x+y+z = 1, 0.6≤x≤1, 0≤y≤0.4, 0≤z≤0.4. Optionally, x is 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or 1. Optionally, y is 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or 0.4. Optionally, z is 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or 0.4.

[0051] In some embodiments, the molar ratio m of the flux to the nickel-cobalt-manganese precursor is 0.001

[0052] In one of the embodiments, the mixed raw materials are subjected to two-stage high-temperature calcination with temperature gradually decreasing in stages, the first-stage high-temperature calcination is performed at a temperature of 980-1050°C for a constant temperature time of 0.1-2 hours, and the second-stage high-temperature calcination is performed at a temperature of 900-980°C for a constant temperature time of 2-24 hours. At the relatively low temperature and time of the second-stage high-temperature calcination, the internal structure of the positive electrode material is repaired, and the effect of reducing lithium-nickel mixing is better, so that a positive electrode material with less grain boundary and less agglomerate can be prepared.

[0053] Optionally, the temperature of the first high-temperature calcination is 980℃, 990℃, 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, or 1050℃. Optionally, the constant temperature time of the first high-temperature calcination is 0.1h, 0.2h, 0.3h, 0.4h, 0.5h, 0.8h, 1h, 1.2h, 1.4h, 1.5h, 1.6h, 1.8h, or 2h. Optionally, the temperature of the second high-temperature calcination is 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, 960℃, 970℃, or 980℃. Optionally, the constant temperature time of the second high-temperature calcination is 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, or 24h.

[0054] In some embodiments, the temperature increasing rate of the high-temperature calcination is 3℃ / min-6℃ / min. Optionally, the temperature increasing rate of the high-temperature calcination is 3℃ / min, 4℃ / min, 5℃ / min, or 6℃ / min.

[0055] In some embodiments, after the pre-product low-temperature calcination, the temperature is decreased to below 200℃ at a rate of 2℃ / min-10℃ / min. Optionally, the temperature decreasing rate to below 200℃ is 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min.

[0056] In one of the embodiments, after the pre-product low-temperature calcination, the temperature is decreased to 200℃ at a rate of 2℃ / min-10℃ / min, and then naturally cooled to room temperature.

[0057] In one of the embodiments, after the high-temperature calcination of the mixed raw materials, the temperature is decreased to below 200℃ at a rate of 2℃ / min-10℃ / min. Optionally, the temperature decreasing rate to below 200℃ is 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min.

[0058] In one of the embodiments, after the high-temperature calcination of the mixed raw materials, the temperature is decreased to below 200℃ at a rate of 2℃ / min-10℃ / min, and then naturally cooled to room temperature to obtain a pre-product, and then low-temperature calcination is performed.

[0059] In one of the embodiments, the room temperature is 25℃.

[0060] In one of the embodiments, it further comprises washing the pre-product after crushing with deionized water, and then drying.

[0061] In one embodiment, the number of times of washing with deionized water is multiple. Optionally, the number of times of washing with deionized water is 2, 3, 4, 5 or 6.

[0062] In one embodiment, the drying is vacuum drying at 120℃ for 3 hours.

[0063] In one embodiment, the product after low-temperature calcination is further sieved.

[0064] In one embodiment, the sieving is through a 325 mesh sieve.

[0065] Another embodiment of the present application provides a positive electrode material prepared by any of the above preparation methods.

[0066] Another embodiment of the present application provides a positive electrode tab, comprising a current collector and an active layer on at least one surface of the current collector, wherein the active layer comprises the positive electrode material prepared by any of the above preparation methods or the positive electrode material described above.

[0067] Another embodiment of the present application provides a lithium ion battery comprising the positive electrode tab described above.

[0068] The following are specific embodiments

[0069] Embodiment 1

[0070] LiOH·H2O (444.5g, 10.6mol), Ni 0.6 Co 0.1 Mn 0.3 (OH)2(916.1g, 10mol) and NaCl (29.2g, 0.5mol) were added into a V-type mixer and mixed for 5 hours to obtain a mixture. The mixture was transferred into a sagger and heated to 1000℃ at a heating rate of 5℃ / min under an oxygen atmosphere, kept at 1000℃ for 2 hours, cooled to 900℃ at a cooling rate of 3℃ / min, kept at 900℃ for 15 hours, cooled to below 200℃ at a cooling rate of 3℃ / min, and then naturally cooled to room temperature to obtain a positive electrode material pre-product. The positive electrode material pre-product was crushed, washed with deionized water three times, vacuum dried at 120℃ for 3 hours, then heated to 750℃ at a heating rate of 10℃ / min, kept at 750℃ for 6 hours, cooled to below 200℃ at a cooling rate of 3℃ / min, and then naturally cooled to room temperature, and sieved through a 325 mesh sieve to obtain a positive electrode material.

[0071] Electrochemical test: The cathode material obtained from Example 1 was mixed with conductive carbon, PVDF (polyvinylidene fluoride) binder in the ratio of 90:5:5 (mass ratio) in NMP (N-methyl pyrrolidone) and coated on an aluminum foil to obtain a cathode sheet. The cathode sheet was dried in a 80°C air oven and then put into a vacuum oven at 120°C overnight. The dried cathode sheet was used as the cathode of a battery, lithium metal as the anode of the battery, a single layer of polyethylene film as the separator, and 1M LiPF6-EC-EMC (i.e. LiPF6 concentration of 1M in EC-EMC solvent, where EC is ethylene carbonate and EMC is methyl ethyl carbonate, the volume ratio of EC: EMC is 3:7) as the electrolyte, to assemble a 2032 battery for electrochemical test.

[0072] Example 2

[0073] LiOH-H2O (444.5 g, 10.6 mol), Ni 0.6 Co 0.1 Mn 0.3 (OH)2(916.1 g, 10 mol) and NaCl (29.2 g, 0.5 mol) were added into a V-type mixer and mixed for 5 hours to obtain a mixture. The mixture was transferred into a die and heated to 980°C at a heating rate of 5°C / min under an oxygen atmosphere, kept at 980°C for 2 hours, cooled to 900°C at a cooling rate of 3°C / min, kept at 900°C for 15 hours, cooled to below 200°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature to obtain a cathode material pre-product. The cathode material pre-product was crushed, washed with deionized water three times, vacuum dried at 120°C for 3 hours, then heated to 750°C at a heating rate of 10°C / min, kept at 750°C for 6 hours, cooled to below 200°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature, and sieved through a 325 mesh screen to obtain the cathode material.

[0074] Electrochemical test: The cathode material obtained from Example 2 was mixed with conductive carbon, PVDF (polyvinylidene fluoride) binder in the ratio of 90:5:5 (mass ratio) in NMP (N-methyl pyrrolidone) and coated on an aluminum foil to obtain a cathode sheet. The cathode sheet was dried in a 80°C air oven and then put into a vacuum oven at 120°C overnight. The dried cathode sheet was used as the cathode of a battery, lithium metal as the anode of the battery, a single layer of polyethylene film as the separator, and 1M LiPF6-EC-EMC (i.e. LiPF6 concentration of 1M in EC-EMC solvent, where EC is ethylene carbonate and EMC is methyl ethyl carbonate, the volume ratio of EC: EMC is 3:7) as the electrolyte, to assemble a 2032 battery for electrochemical test.

[0075] Example 3

[0076] LiOH-H20 (460.0 g, 11 mol), Ni 0.6 Co 0.1 Mn 0.3 (OH)2(916.1 g, 10 mol) and NaCl (29.2 g, 0.5 mol) were added into a V-type mixer and mixed for 5 hours to obtain a mixture. The mixture was transferred into a die and heated to 980°C at a heating rate of 5°C / min under an oxygen atmosphere, kept at 980°C for 2 hours, cooled to 900°C at a cooling rate of 3°C / min, kept at 900°C for 15 hours, cooled to below 200°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature to obtain a positive electrode material pre-product. The positive electrode material pre-product was crushed, washed with deionized water for three times, vacuum dried at 120°C for 3 hours, then heated to 750°C at a heating rate of 10°C / min, kept at 750°C for 6 hours, cooled to below 200°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature, and passed through a 325 mesh sieve to obtain a positive electrode material.

[0077] Electrochemical test: the positive electrode material obtained in Example 3 was mixed with conductive carbon and PVDF (polyvinylidene fluoride) binder in a ratio of 90:5:5 (mass ratio) in NMP (N-methyl pyrrolidone) and then coated on an aluminum foil to obtain a pole piece. The pole piece was dried in a 80°C air oven and then placed in a 120°C vacuum oven for drying overnight. The dried pole piece was used as a battery positive electrode, lithium metal was used as a battery negative electrode, a single layer of polyethylene film was used as a separator, and 1M LiPF6-EC-EMC (i.e., the concentration of LiPF6 in EC-EMC solvent is 1M, wherein EC is ethylene carbonate and EMC is methyl ethyl carbonate, and the volume ratio of EC: EMC is 3:7) was used as an electrolyte to assemble a 2032 battery for electrochemical test.

[0078] Example 4

[0079] LiOH-H20 (460.0 g, 11 mol), Ni 0.6 Co 0.1 Mn 0.3LiOH-H20 (444.5 g, 10.6 mol) and NaCl (58.4 g, 1 mol) were added into a V-type mixer and mixed for 5 hours to obtain a mixture, the mixture was transferred into a crucible, heated to 980 °C at a heating rate of 5 °C / min under oxygen atmosphere, kept for 2 hours, cooled to 900 °C at a cooling rate of 3 °C / min, kept for 15 hours, cooled to below 200 °C at a cooling rate of 3 °C / min, and then naturally cooled to room temperature to obtain a positive electrode material pre-product. The positive electrode material pre-product was crushed, washed with deionized water for three times, vacuum dried at 120 °C for 3 hours, then heated to 750 °C at a heating rate of 10 °C / min, kept for 6 hours, cooled to below 200 °C at a cooling rate of 3 °C / min, and then naturally cooled to room temperature, and sieved through a 325 mesh screen to obtain the positive electrode material.

[0080] Electrochemical test: the positive electrode material obtained in Example 4 was mixed with conductive carbon and PVDF (polyvinylidene fluoride) binder in a ratio of 90:5:5 (mass ratio) in NMP (N-methyl pyrrolidone) to coat an aluminum foil to obtain a pole piece. The pole piece was dried in a 80 °C air oven and then placed in a 120 °C vacuum oven to dry overnight. The dried pole piece was used as a battery positive electrode, lithium metal as a battery negative electrode, a single layer of polyethylene film as a separator, and 1M LiPF6-EC-EMC (i.e. the concentration of LiPF6 in EC-EMC solvent is 1M, wherein EC is ethylene carbonate and EMC is methyl ethyl carbonate, and the volume ratio of EC: EMC is 3:7) as an electrolyte to assemble a 2032 battery for electrochemical test.

[0081] Example 5

[0082] LiOH-H20 (444.5 g, 10.6 mol), Ni 0.6 Co 0.1 Mn 0.3 LiOH-H20 (444.5 g, 10.6 mol) and KCl (37.3 g, 0.5 mol) were added into a V-type mixer and mixed for 5 hours to obtain a mixture, the mixture was transferred into a crucible, heated to 980 °C at a heating rate of 5 °C / min under oxygen atmosphere, kept for 2 hours, cooled to 900 °C at a cooling rate of 3 °C / min, kept for 15 hours, cooled to below 200 °C at a cooling rate of 3 °C / min, and then naturally cooled to room temperature to obtain a positive electrode material pre-product. The positive electrode material pre-product was crushed, washed with deionized water for three times, vacuum dried at 120 °C for 3 hours, then heated to 750 °C at a heating rate of 10 °C / min, kept for 6 hours, cooled to below 200 °C at a cooling rate of 3 °C / min, and then naturally cooled to room temperature, and sieved through a 325 mesh screen to obtain the positive electrode material.

[0083] Electrochemical test: The cathode material obtained in Example 5 was mixed with conductive carbon, PVDF (polyvinylidene fluoride) binder in a ratio of 90:5:5 (mass ratio) in NMP (N-methyl pyrrolidone) and coated on an aluminum foil to obtain a pole piece. The pole piece was dried in a 80°C air oven and then put into a 120°C vacuum oven to dry overnight. The dried pole piece was used as the cathode of a battery, lithium metal as the anode of the battery, a single layer of polyethylene film as the separator, 1M LiPF6-EC-EMC (i.e. the concentration of LiPF6 in EC-EMC solvent is 1M, where EC is ethylene carbonate and EMC is methyl ethyl carbonate, the volume ratio of EC: EMC is 3:7) as the electrolyte, and assembled into a 2032 battery for electrochemical test.

[0084] Example 6

[0085] LiOH-H2O (444.5 g, 10.6 mol), Ni 0.6 Co 0.1 Mn 0.3 (OH)2(916.1 g, 10 mol) and KCl (37.3 g, 0.5 mol) were added into a V-type mixer and mixed for 5 hours to obtain a mixture. The mixture was transferred into a die and heated to 980°C at a heating rate of 5°C / min under an oxygen atmosphere, kept at 980°C for 1 hour, cooled to 920°C at a cooling rate of 3°C / min, kept at 920°C for 4 hours, cooled to 900°C at a cooling rate of 3°C / min, kept at 900°C for 7 hours, and then cooled to below 200°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature to obtain a cathode material pre-product. The cathode material pre-product was crushed, washed with deionized water three times, vacuum dried at 120°C for 3 hours, then heated to 750°C at a heating rate of 10°C / min, kept at 750°C for 6 hours, cooled to below 200°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature, and then passed through a 325 mesh sieve to obtain the cathode material.

[0086] Electrochemical test: The cathode material obtained in Example 6 was mixed with conductive carbon, PVDF (polyvinylidene fluoride) binder in a ratio of 90:5:5 (mass ratio) in NMP (N-methyl pyrrolidone) and coated on an aluminum foil to obtain a pole piece. The pole piece was dried in a 80°C air oven and then put into a 120°C vacuum oven to dry overnight. The dried pole piece was used as the cathode of a battery, lithium metal as the anode of the battery, a single layer of polyethylene film as the separator, 1M LiPF6-EC-EMC (i.e. the concentration of LiPF6 in EC-EMC solvent is 1M, where EC is ethylene carbonate and EMC is methyl ethyl carbonate, the volume ratio of EC: EMC is 3:7) as the electrolyte, and assembled into a 2032 battery for electrochemical test.

[0087] Comparative Example 1

[0088] LiOH-H20 (444.5 g, 10.6 mol), Ni 0.6 Co 0.1 Mn 0.3 (OH)2(916.1 g, 10 mol) and NaCl (29.2 g, 0.5 mol) were added into a V-type mixer and mixed for 5 hours to obtain a mixture. The mixture was transferred into a crucible and heated to 980 °C at a heating rate of 5 °C / min under an oxygen atmosphere, kept at 980 °C for 15 hours, cooled to below 200 °C at a cooling rate of 3 °C / min, and then naturally cooled to room temperature to obtain a positive electrode material pre-product. The positive electrode material pre-product was crushed, washed with deionized water three times, vacuum dried at 120 °C for 3 hours, then heated to 750 °C at a heating rate of 10 °C / min, kept at 750 °C for 6 hours, cooled to below 200 °C at a cooling rate of 3 °C / min, and then naturally cooled to room temperature, and sieved through a 325 mesh screen to obtain the positive electrode material.

[0089] Electrochemical test: the positive electrode material obtained in Comparative Example 1 was mixed with conductive carbon and a PVDF (polyvinylidene fluoride) binder in a ratio of 90:5:5 (mass ratio) in NMP (N-methyl pyrrolidone) to obtain a pole piece. The pole piece was dried in a 80 °C air oven and then placed in a 120 °C vacuum oven to dry overnight. The dried pole piece was used as a battery positive electrode, lithium metal was used as a battery negative electrode, a single layer of polyethylene film was used as a separator, and 1M LiPF6-EC-EMC (i.e. the concentration of LiPF6 in the EC-EMC solvent is 1M, where EC is ethylene carbonate and EMC is methyl ethyl carbonate, and the volume ratio of EC:EMC is 3:7) was used as an electrolyte to assemble a 2032 battery for electrochemical test.

[0090] Comparative Example 2

[0091] LiOH-H20 (444.5 g, 10.6 mol), Ni 0.6 Co 0.1 Mn 0.3 (OH)2(916.1 g, 10 mol) and NaCl (29.2 g, 0.5 mol) were added into a V-type mixer and mixed for 5 hours to obtain a mixture. The mixture was transferred into a crucible and heated to 980 °C at a heating rate of 5 °C / min under an oxygen atmosphere, kept at 980 °C for 15 hours, cooled to below 200 °C at a cooling rate of 3 °C / min, and then naturally cooled to room temperature to obtain a positive electrode material pre-product. The positive electrode material pre-product was crushed, washed with deionized water three times, vacuum dried at 120 °C for 3 hours, then heated to 750 °C at a heating rate of 10 °C / min, kept at 750 °C for 6 hours, cooled to below 200 °C at a cooling rate of 3 °C / min, and then naturally cooled to room temperature, and sieved through a 325 mesh screen to obtain the positive electrode material.

[0092] Electrochemical test: The cathode material obtained from Comparative Example 2 was mixed with conductive carbon and PVDF (polyvinylidene fluoride) binder in a ratio of 90:5:5 (mass ratio) in NMP (N-methyl pyrrolidone) and coated on an aluminum foil to obtain a pole piece. The pole piece was dried in a 80°C air oven and then placed in a 120°C vacuum oven to dry overnight. The dried pole piece was used as the positive electrode of a battery, lithium metal as the negative electrode of the battery, a single layer of polyethylene film as the separator, and 1M LiPF6-EC-EMC (i.e. the concentration of LiPF6 in EC-EMC solvent is 1M, wherein EC is ethylene carbonate and EMC is methyl ethyl carbonate, and the volume ratio of EC: EMC is 3:7) as the electrolyte to assemble a 2032 battery for electrochemical test.

[0093] Comparative Example 3

[0094] LiOH-H2O (630.0 g, 15 mol), Ni 0.6 Co 0.1 Mn 0.3 (OH)2(916.1 g, 10 mol) and NaCl (29.2 g, 0.5 mol) were added to a V-type mixer and mixed for 5 hours to obtain a mixture. The mixture was transferred to a die and heated to 900°C at a heating rate of 5°C / min under an oxygen atmosphere, kept at 900°C for 15 hours, and then cooled to below 200°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature to obtain a cathode material pre-product. The cathode material pre-product was crushed, washed with deionized water three times, vacuum dried at 120°C for 3 hours, then heated to 750°C at a heating rate of 10°C / min, kept at 750°C for 6 hours, cooled to below 200°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature, and then sieved through a 325 mesh screen to obtain a cathode material.

[0095] Electrochemical test: The cathode material obtained from Comparative Example 3 was mixed with conductive carbon and PVDF (polyvinylidene fluoride) binder in a ratio of 90:5:5 (mass ratio) in NMP (N-methyl pyrrolidone) and coated on an aluminum foil to obtain a pole piece. The pole piece was dried in a 80°C air oven and then placed in a 120°C vacuum oven to dry overnight. The dried pole piece was used as the positive electrode of a battery, lithium metal as the negative electrode of the battery, a single layer of polyethylene film as the separator, and 1M LiPF6-EC-EMC (i.e. the concentration of LiPF6 in EC-EMC solvent is 1M, wherein EC is ethylene carbonate and EMC is methyl ethyl carbonate, and the volume ratio of EC: EMC is 3:7) as the electrolyte to assemble a 2032 battery for electrochemical test.

[0096] Comparative Example 4

[0097] LiOH-H2O (444.5 g, 10.6 mol) and Ni 0.6 Co0.1 Mn 0.3 (OH)2(916.1g, 10mol) were added into a V-type mixer and mixed for 5 hours to obtain a mixture. The mixture was transferred into a die and heated to 900°C at a heating rate of 5°C / min under an oxygen atmosphere, kept at 900°C for 15 hours, and then cooled to below 200°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature to obtain a positive electrode material pre-product. The positive electrode material pre-product was crushed, washed with deionized water three times, vacuum dried at 120°C for 3 hours, and then heated to 750°C at a heating rate of 10°C / min, kept at 750°C for 6 hours, and then cooled to below 200°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature, and then sieved through a 325 mesh sieve to obtain the positive electrode material.

[0098] Electrochemical test: the positive electrode material obtained in Comparative Example 4 was mixed with conductive carbon and a PVDF (polyvinylidene fluoride) binder in a ratio of 90:5:5 (mass ratio) in NMP (N-methyl pyrrolidone) to coat an aluminum foil to obtain an electrode sheet. The electrode sheet was dried in a 80°C air oven and then placed in a 120°C vacuum oven to dry overnight. The dried electrode sheet was used as a positive electrode of a battery, lithium metal was used as a negative electrode of the battery, a single-layer polyethylene film was used as a separator, and 1M LiPF6-EC-EMC (i.e., the concentration of LiPF6 in the EC-EMC solvent is 1M, wherein EC is ethylene carbonate and EMC is methyl ethyl carbonate, and the volume ratio of EC:EMC is 3:7) was used as an electrolyte to assemble a 2032 battery for electrochemical test.

[0099] Reference Figures 1-10 As can be seen from the SEM images, the positive electrode materials in Examples 1-6 have less particle agglomeration and grain boundaries. In Example 3, the particle size is larger due to the increase in the amount of LiOH-H2O. In Comparative Examples 1-4, in Comparative Example 1, the particle size is larger due to only one high-temperature calcination and a high sintering temperature. In Comparative Example 2, there are more agglomerates and grain boundaries due to only one high-temperature calcination and a relatively low sintering temperature. In Comparative Example 3, the content of Li source is high, and the positive electrode material with less agglomeration and grain boundaries can be formed at a low temperature. In Comparative Example 4, there are many agglomerates and the particles are obviously irregular due to the absence of inorganic molten salt.

[0100] The batteries assembled from Examples 1-6 and Comparative Examples 1-4 were subjected to electrochemical test. The test method was as follows: a constant current charge-discharge tester was used for the test, the test conditions were 25°C, 2.8-4.45V vs Li+ / Li, the first cycle was tested at a rate of 0.1C charge / 0.1C discharge, and the following 50 cycles were tested at a rate of 1C charge / 1C discharge. The first discharge specific capacity, the first coulombic efficiency, and the capacity retention rate after 50 cycles are shown in Table 1.

[0101] Table 1

[0102]

[0103] At the same time, reducing the content of Li source can reduce the cost, reduce the adhesion and corrosion to the saggar. The saggar life in Examples 1-6 and Comparative Examples 1-4 is shown in Table 2 below:

[0104] Table 2

[0105]

[0106]

[0107] By reducing the content of Li source in Examples 1-6, the adhesion and corrosion to the saggar can be reduced, the number of repeated use of the saggar is higher, the cost is saved, at the same time, the positive electrode material with less grain boundary and agglomerate can be obtained. Further, the battery assembled by the positive electrode material in Examples 1-6 also has good initial specific discharge capacity, initial coulombic efficiency and 50 cycle capacity retention rate.

[0108] The technical features of the above-described embodiments can be combined arbitrarily, and for the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the present disclosure.

[0109] The above-described embodiments only express several implementation manners of the present application, the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of variations and improvements can be made, which are all within the scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims, the description and the drawings can be used to explain the content of the claims.

Claims

1. A method for producing a positive electrode material, characterized by, Comprising: A Li source, a fluxing agent, and a nickel-cobalt-manganese precursor including Ni x Co y Mn z (OH)2, where x+y+z = 1, 0.6 < x < 1, 0 < y < 0.4, and 0 < z < 0.4 carrying out two-stage high-temperature calcination on the mixed raw materials, the temperature of the first stage of high-temperature calcination being 980-1050 DEG C, the constant temperature time being 0.1-2 h, the temperature of the second stage of high-temperature calcination being 900-980 DEG C, the constant temperature time being 2-24 h, to obtain a pre-product; carrying out low-temperature calcination on the pre-product, the temperature of the low-temperature calcination being 650-890 DEG C; the molar ratio n of Li atoms in the Li source to the nickel-cobalt-manganese precursor is 0.5 The fluxing agent includes an inorganic salt MX, wherein M includes at least one of Li + , Na + , K + , Rb + , Cs + , Mg 2+ , Ca 2+ , Sr 2+ , and Ba 2+ , and X includes at least one of F - , Cl - , Br - , I - , NO3 - , and SO4 2- .

2. The method of claim 1, wherein the method is characterized by: the time of the low-temperature calcination is 3-10 h.

3. The method for preparing the cathode material according to claim 1, characterized in that, The Li source comprises one or more of LiOH, LiOH·H2O, Li2CO3, LiNO3 and CH3COOLi.

4. The method of claim 1, wherein the method further comprises: The molar ratio m of the fluxing agent to the nickel-cobalt-manganese precursor is 0.001 5. The method of claim 1 to 4, characterized in that The heating rate of the high-temperature calcination is 3-6 DEG C / min; and / or, after the low-temperature calcination of the pre-product, the temperature is lowered to below 200 DEG C at a cooling rate of 2-10 DEG C / min.

6. A positive electrode material, characterized by, Prepared by the preparation method of any one of claims 1-5.

7. A positive electrode sheet characterized by comprising: Comprising a current collector and an active layer on at least one surface of the current collector, the active layer comprising the positive electrode material prepared by the preparation method of any one of claims 1-5 or the positive electrode material of claim 6.

8. A lithium-ion battery, characterized by, Comprising the positive electrode sheet of claim 7.

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