A rock salt structured full concentration gradient cathode material, its preparation method and application

Abstract

This invention provides a rock-salt structured full-concentration gradient cathode material, its preparation method, and its application. The preparation method includes the following steps: (1) mixing a full-concentration gradient structure precursor with a lithium source and performing a first sintering treatment under an oxygen-containing atmosphere to obtain a sintered material; (2) performing a second sintering treatment on the sintered material under an oxygen-free atmosphere to obtain the rock-salt structured full-concentration gradient cathode material; in the full-concentration gradient structure precursor, the concentration of nickel decreases gradually from the core to the surface. This invention uses a combination of surface rock-salt phase and full-concentration gradient structure design, which can reduce the side reactions at the cathode material interface while suppressing the generation of microcracks, resulting in better cycle performance of the cathode material.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and relates to a rock salt structure full concentration gradient cathode material, its preparation method and application. Background Technology

[0002] In recent years, the global electric vehicle and robotics industries have flourished, and ternary lithium-ion batteries have been widely adopted due to their high capacity and controllable cost. With the further expansion of the industry and increased competition, higher demands are being placed on the capacity and safety of ternary lithium-ion batteries. Increasing the operating voltage and increasing the nickel content are new solutions to overcome the capacity bottlenecks of existing ternary lithium batteries. The development of electrolytes for industrial-scale application under high-voltage conditions is progressing slowly; therefore, increasing the nickel content of ternary cathodes is a more realistic breakthrough path in the short term.

[0003] Ni on the surface of high-nickel cathode material under high temperature and deep delithiation conditions 3+ A disproportionation reaction will occur, producing Ni. 2+ and Ni 4+ Ni 4+ It has strong oxidizing properties and will directly react with the electrolyte in contact with it, causing interfacial side reactions that catalyze the decomposition products of the electrolyte, such as HF and CO2, to corrode the positive electrode surface. Furthermore, Ni... 4+ The strong polarization effect on oxygen ions leads to the oxidation of the lattice pattern to O. 2 Precipitation occurs, forming oxygen vacancies; Ni 2+ Because of Li + With similar radii, they easily migrate from the transition metal layer to the lithium layer, resulting in cation mixing.

[0004] CN113903903A discloses a method for preparing a doped and modified high-nickel cathode material. The method involves reacting a high-nickel precursor with an oxidant under certain conditions to form an active hydroxyl oxide. The active hydroxyl oxide is then subjected to an ion exchange reaction with a lithium salt and a doped metal salt to obtain an amorphous high-nickel cathode material. Finally, the desired cathode material is obtained by high-temperature crystallization.

[0005] CN120413632A discloses a method for preparing and applying a high-nickel cathode material with a core-shell structure. By controlling the calcination conditions of the high-nickel cathode material in an oxygen-free environment, the oxygen vacancies on the material surface are regulated to synthesize a sample with a core-shell structure, which significantly improves the specific capacity and cycle stability of the layered cathode material under deep charge and discharge conditions.

[0006] The above-mentioned scheme constructs a thin layer of rock salt phase on the cathode surface by doping with high-valence cations during high-temperature sintering or by mechanically mixing the precursor with the lithium source and sintering at high temperature. However, the introduction of inactive heteroatoms will reduce the charge and discharge capacity of the cathode material. Another method to form the rock salt surface phase is to mechanically ball-mill and mix the precursor and the lithium source and then sinter at high temperature. The thickness and uniformity of the rock salt phase generated by this method are uncontrollable. Summary of the Invention

[0007] The purpose of this invention is to provide a rock salt structure full concentration gradient cathode material, its preparation method and application. This invention uses a combination of surface rock salt phase and full concentration gradient structure design, which can reduce the side reactions at the cathode material interface and suppress the problem of microcracks causing exposure of highly active internal interfaces, so that the cathode material exhibits better cycle performance.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a rock salt structured full-concentration gradient cathode material, the preparation method comprising the following steps:

[0010] (1) The full concentration gradient structure precursor was mixed with a lithium source and subjected to a first sintering treatment in an oxygen-containing atmosphere to obtain a sintered material.

[0011] (2) The first sintering material is subjected to a second sintering treatment in an oxygen-free atmosphere to obtain the rock salt structure full concentration gradient cathode material;

[0012] In the full concentration gradient structure precursor, the concentration of nickel decreases in a gradient from the core to the surface.

[0013] This invention uses a full-concentration gradient structure precursor as a matrix to alleviate microcracks caused by heterogeneous stress accumulation within the cathode material during charge-discharge cycles, as it reduces the surface Ni content and thus suppresses side reactions at the cathode-electrolyte interface. The lithiated high-nickel cathode material with a full-concentration gradient structure is then sintered a second time in an oxygen-free atmosphere. In this high-nickel cathode material, the nickel content gradually decreases from the core to the surface, while the manganese and cobalt contents gradually increase. First, lithiation in an oxygen atmosphere forms a layered, ordered matrix. Then, a second sintering in an oxygen-free atmosphere causes the manganese- and cobalt-rich surface to decompose or partially lose lithium at high temperatures, resulting in a disordered yet uniform rock salt phase thin layer on the surface of the full-concentration gradient structure cathode material matrix. This disordered rock salt phase not only has structural compatibility with the ordered layered structure but also maintains good electrochemical matching. Furthermore, the rock salt phase is an electronic insulator, which can reduce the highly active Ni on the surface of the high-nickel cathode. 4+Direct contact with the electrolyte reduces interfacial side reactions between the electrolyte and the cathode material, preventing the dissolution of some transition metals. Furthermore, the formation of a thin rock-salt phase layer consumes the surface-unstable Ni. 4+ Lattice oxygen can reduce further oxygen loss from the bulk material and suppress more severe surface reconstruction.

[0014] Preferably, the full-concentration gradient structure precursor described in step (1) is prepared by the following method:

[0015] A first mixed salt solution is pre-set in a mixing tank. The first mixed salt solution is injected into the mixing tank at a flow rate L1 and the second mixed salt solution is injected into the mixing tank at a flow rate L2. At the same time, the liquid in the mixing tank is injected into the bottom liquid in parallel with the precipitant solution and the complexing agent solution at a flow rate L to carry out a co-precipitation reaction, thereby obtaining the full concentration gradient structure cathode precursor.

[0016] In the full-concentration gradient structure cathode precursor prepared by the method of the present invention, the nickel content gradually decreases from the core to the surface, while the manganese and cobalt contents gradually increase.

[0017] Preferably, the molar ratio of nickel, cobalt and manganese in the first mixed salt solution is a:b:c, wherein a is 0.9 to 1.0, b is 0 to 0.1, c is 0 to 0.1, and a+b+c=1.

[0018] Preferably, the total molar concentration of metal ions in the first mixed salt solution is 1 mol / L to 3 mol / L.

[0019] Preferably, the molar ratio of nickel, cobalt and manganese in the second mixed salt solution is x:y:z, where x is 0.6 to 0.89, y is 0.11 to 0.4, z is 0.11 to 0.4, and x+y+z=1.

[0020] Preferably, the total molar concentration of metal ions in the second mixed salt solution is 1.5 mol / L to 2.5 mol / L, for example: 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L or 2.5 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, with the volume of the mixing tank being 100%, the volume of the first mixed salt solution pre-set in the mixing tank is 20% to 100%, for example: 20%, 40%, 60%, 80% or 100%, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0022] Preferably, with the volume of the solution required for the coprecipitation reaction being 100%, the volume of the mixing tank is 10% to 100%, for example: 10%, 20%, 60%, 80% or 100%, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable, preferably 20% to 40%.

[0023] Preferably, the volume of the reaction apparatus used for the coprecipitation reaction is vL, and the volume of the mixing tank is 0.2vL to 1.0vL, for example: 0.2vL, 0.4vL, 0.6vL, 0.8vL or 1.0vL, etc.

[0024] Preferably, the flow rate L1 of the first mixed salt solution is 0.5% vL / h to 1% vL / h, for example: 0.5% vL / h, 0.6% vL / h, 0.7% vL / h, 0.8% vL / h or 1% vL / h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] Preferably, the flow rate L2 of the second mixed salt solution is 1% vL / h to 1.5% vL / h, for example: 1% vL / h, 1.2% vL / h, 1.25% vL / h, 1.4% vL / h or 1.5% vL / h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] Preferably, the flow rate L of the liquid in the mixing tank is 2% vL / h to 3% vL / h, for example: 2% vL / h, 2.2% vL / h, 2.5% vL / h, 2.8% vL / h or 3% vL / h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] Preferably, L > L1 + L2.

[0028] Preferably, the precipitant solution comprises any one or a combination of at least two of sodium hydroxide solution, potassium hydroxide solution, or sodium carbonate solution. Typical but non-limiting combinations include combinations of sodium hydroxide solution and potassium hydroxide solution, combinations of sodium hydroxide solution and sodium carbonate solution, or combinations of potassium hydroxide solution and sodium carbonate solution, etc.

[0029] Preferably, the mass percentage concentration of the precipitant solution is 10% to 40%, for example: 10%, 15%, 20%, 30% or 40%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Preferably, the complexing agent solution comprises any one or a combination of at least two of ammonia, oxalic acid, citric acid, or ammonium bicarbonate solution. Typical but non-limiting combinations include a combination of ammonia and ammonium bicarbonate solution, a combination of oxalic acid and citric acid solution, or a combination of oxalic acid and ammonium bicarbonate solution, etc.

[0031] Preferably, the mass percentage concentration of the complexing agent solution is 10% to 40%, for example: 10%, 15%, 20%, 30% or 40%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] Preferably, the base liquid comprises a precipitant, a complexing agent, and water.

[0033] Preferably, the pH of the base solution is 11 to 12, such as 11, 11.2, 11.5, 11.8 or 12, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] Preferably, the mass concentration of the complexing agent in the base liquid is 1 g / L to 9 g / L, for example: 1 g / L, 2 g / L, 5 g / L, 7 g / L or 9 g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Preferably, the temperature of the coprecipitation reaction is 50℃~70℃, for example: 50℃, 55℃, 60℃, 65℃ or 70℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] Preferably, the pH of the coprecipitation reaction is 9.5 to 11, for example: 9.5, 9.8, 10, 10.5 or 11, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] The mixing tank and the reaction vessel used in the co-precipitation reaction described in this invention are both equipped with stirrers. The stirrer in the mixing tank is used to mix the ultra-high nickel salt solution and the high nickel salt solution evenly. The stirrer in the reaction vessel is used to mix the salt solution with the precipitant and the complexing agent evenly and to ensure complete precipitation reaction. In the reaction system, the different salt solutions are mixed thoroughly, and there will be no situation where the element ratio of the salt solution pumped into the reaction vessel changes greatly, resulting in insufficient complexation and the appearance of small particles.

[0038] Preferably, the atmosphere for the coprecipitation reaction is any one or a combination of at least two of nitrogen, argon, or helium. Typical but non-limiting combinations include combinations of argon and nitrogen, argon and helium, or nitrogen and helium.

[0039] Preferably, the volume of the reactor is m, and the flow rate of the atmosphere is 0.1 m / h to 4 m / h, for example: 0.1 m / h, 0.5 m / h, 1 m / h, 2 m / h or 4 m / h, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0040] Preferably, the lithium source in step (1) includes any one or a combination of at least two of lithium hydroxide, lithium carbonate, lithium sulfate, or lithium phosphate.

[0041] Preferably, the molar ratio of the full concentration gradient structure precursor to lithium in the lithium source in step (1) is 1:(1 to 1.1), for example: 1:1, 1:1.02, 1:1.05, 1:1.08 or 1:1.1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] Preferably, the oxygen-containing atmosphere in step (1) includes any one or a combination of at least two of oxygen, compressed air, or nitrogen dioxide.

[0043] Preferably, step (1) the first sintering treatment includes a first calcination and a second calcination.

[0044] Preferably, the temperature of the first calcination is 450℃~550℃, for example: 450℃, 480℃, 500℃, 520℃ or 550℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] Preferably, the first calcination time is 2h to 6h, for example: 2h, 3h, 4h, 5h or 6h, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0046] Preferably, the second calcination temperature is 700℃~800℃, for example: 700℃, 720℃, 750℃, 780℃ or 800℃, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0047] Preferably, the second calcination time is 10h to 20h, for example: 10h, 12h, 15h, 18h or 20h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] Preferably, the first sintering treatment is followed by furnace cooling.

[0049] Preferably, the oxygen-free atmosphere in step (2) includes any one or a combination of at least two of argon, nitrogen, helium or a hydrogen-argon mixture.

[0050] Preferably, the temperature of the second sintering treatment in step (2) is 400℃~600℃, for example: 400℃, 450℃, 500℃, 550℃ or 600℃, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0051] Preferably, the second sintering treatment time in step (2) is 4h to 8h, for example: 4h, 5h, 6h, 7h or 8h, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0052] In a second aspect, the present invention provides a rock salt structure full concentration gradient cathode material, which is prepared by the preparation method described in the first aspect.

[0053] Thirdly, the present invention provides a positive electrode sheet comprising a rock salt structure full concentration gradient positive electrode material as described in the second aspect.

[0054] Preferably, the rock salt structure full concentration gradient cathode material includes a full concentration gradient cathode core and a disordered rock salt phase coating layer disposed on the surface of the full concentration gradient cathode core.

[0055] The rock salt structure in the full-concentration gradient cathode material described in this invention is in a disordered state. This disordered rock salt layer, due to its unique disordered structure, provides a fundamental solution to the structural instability problem under high delithiation conditions. Crucially, the disordered rock salt phase and the ordered layered structure not only possess structural compatibility but also maintain excellent electrochemical matching. This unique compatibility allows it to effectively compensate for the key performance defects of ordered layered oxide materials.

[0056] Preferably, the thickness of the disordered rock salt phase coating layer is 5nm to 30nm, for example: 5nm, 8nm, 10nm, 20nm or 30nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0057] The rock salt phase described in this invention, as an inactive material, reduces the charge and discharge capacity of the positive electrode. However, under certain conditions, a thin and uniform rock salt phase layer can provide some protection for the positive electrode material.

[0058] Fourthly, the present invention provides a lithium-ion battery comprising a positive electrode as described in the third aspect.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] (1) The present invention uses a combination of surface rock salt phase and full concentration gradient structure design, which can reduce the side reactions at the interface of the cathode material and suppress the problem of microcracks causing high-activity internal interface exposure, so that the cathode material exhibits better cycle performance.

[0061] (2) The method of the present invention produces a battery with a rock salt structure full concentration gradient cathode material. The battery has a 0.1C first discharge specific capacity of more than 191.5 mAh / g, a 1C first discharge specific capacity of more than 176.4 mAh / g, and a capacity retention rate of more than 85.6% after 100 cycles. By adjusting the preparation conditions, the battery with a rock salt structure full concentration gradient cathode material can achieve a 0.1C first discharge specific capacity of more than 198.4 mAh / g, a 1C first discharge specific capacity of more than 179.6 mAh / g, and a capacity retention rate of more than 89.2% after 100 cycles. Attached Figure Description

[0062] Figure 1 This is a schematic diagram of the apparatus used in the preparation process of the full concentration gradient structure cathode precursor provided in the embodiments of the present invention, wherein 1 is the first storage tank, 2 is the second storage tank, 3 is the mixing tank, 4 is the reaction vessel, 5 is the stirring paddle, 6 is the complexing agent tank, and 7 is the precipitant tank. Detailed Implementation

[0063] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0064] A schematic diagram of the apparatus used in the preparation of the full concentration gradient structure precursors used in the embodiments and comparative examples of this invention is shown below. Figure 1 As shown, the full concentration gradient structure cathode precursor is prepared by the following method:

[0065] 25 L of a first mixed salt solution and 25 L of a second mixed salt solution were prepared according to the molar ratios Ni:Co:Mn = 96:2:2 and Ni:Co:Mn = 8:1:1, respectively. Both solutions were sulfate solutions with a total molar concentration of 2 mol / L for the metal ions. A 32% NaOH solution was prepared as a precipitant solution, and a 16% ammonia solution was prepared as a complexing agent solution. The ammonia solution was placed in a complexing agent container 6, and the sodium hydroxide solution was placed in a precipitant container 7. The first mixed salt solution is placed in the first storage tank 1 and the mixing tank 3 with a volume of 20L. The second mixed salt solution is placed in the second storage tank 2. The volume of the first mixed salt solution in the mixing tank 3 is 10L, accounting for 50% of the tank volume. Pure water is added to the reaction vessel 4 with a volume of 20L, and NaOH solution is pumped in to control the pH value at 12. Ammonia solution is pumped in to control the ammonia amount at 2.0g / L. The temperature of the vessel is maintained at 58℃ by hydrothermal heating of the vessel body by an external mold temperature controller. The vessel lid is sealed, and a protective atmosphere of N2 is introduced with a nitrogen flow rate of 20L / h.

[0066] The first mixed salt solution in the first storage tank 1 and the second mixed salt solution in the second storage tank 2 were pumped into the mixing tank 3 at rates of 0.15 L / h and 0.25 L / h, respectively, for mixing. Simultaneously, the liquid in the mixing tank 3 was pumped into the reaction vessel along with ammonia and sodium hydroxide solutions at a rate of 0.5 L / h for co-precipitation. The pH of the co-precipitation reaction was 10, the ammonia concentration was 2 g / L, and the initial speed of the dual-paddle stirrer was 800 rpm, which gradually decreased as the particle size increased. The total flow rate of the two salt solutions pumped into the mixing tank was 0.4 L / h, while the flow rate of the solution pumped from the mixing tank into the reaction vessel was 0.5 L / h. The liquid level in the mixing tank gradually decreased at a rate of 0.1 L / h, and the reaction time was 100 h. The precursor particles D... 50 When the particle size reaches 10.0 μm, the mixed solution in the mixing tank is depleted, and feeding is stopped.

[0067] The precursor slurry was transferred to a washing vessel, washed with a 16% NaOH solution and 50°C pure water, and then excess water was filtered out. It was then transferred to a 110°C forced-air drying oven overnight. After sieving and demagnetization, the full-concentration gradient structure cathode precursor was obtained.

[0068] Example 1

[0069] This embodiment provides a rock salt structure full concentration gradient cathode material, which is prepared by the following method:

[0070] (1) The full concentration gradient structure precursor and lithium hydroxide were mixed evenly at a molar ratio of 1:1.05, and then placed in a ceramic boat and put into a tube furnace. Under an oxygen atmosphere, the temperature was first raised at 2℃ / min and held at 500℃ for 5h, and then raised to 750℃ at 2℃ / min and held for 10h. After cooling with the furnace, a calcined material was obtained.

[0071] (2) The material was placed in a nitrogen atmosphere and heated to 500℃ at 2℃ / min and held for 6h before being cooled in the furnace to obtain the rock salt structure full concentration gradient cathode material.

[0072] In the rock salt structure full concentration gradient cathode material, the thickness of the disordered rock salt phase coating layer is 15 nm.

[0073] Example 2

[0074] This embodiment provides a rock salt structure full concentration gradient cathode material, which is prepared by the following method:

[0075] (1) After the full concentration gradient structure precursor and lithium hydroxide are mixed evenly at a molar ratio of 1:1.05, the mixture is placed in a ceramic boat and put into a tube furnace. Under an oxygen atmosphere, the temperature is first raised at 3℃ / min and held at 450℃ for 6h, and then raised to 700℃ at 3℃ / min and held for 15h. After cooling with the furnace, a calcined material is obtained.

[0076] (2) The material was placed in a nitrogen atmosphere and heated to 400℃ at 2℃ / min and held for 8 hours. Then it was cooled with the furnace to obtain the rock salt structure full concentration gradient cathode material.

[0077] In the rock salt structure full concentration gradient cathode material, the thickness of the disordered rock salt phase coating layer is 30 nm.

[0078] Example 3

[0079] This embodiment provides a rock salt structure full concentration gradient cathode material, which is prepared by the following method:

[0080] (1) The full concentration gradient structure precursor and lithium hydroxide were mixed evenly at a molar ratio of 1:1.05, and then placed in a ceramic boat and put into a tube furnace. Under the atmosphere of nitrogen dioxide, the temperature was first raised at 550°C for 2 hours at a heating rate of 5°C / min, and then raised to 800°C for 10 hours at a heating rate of 5°C / min. After cooling with the furnace, a calcined material was obtained.

[0081] (2) The material was placed in an argon atmosphere and heated to 600°C at 5°C / min and held for 4 hours before being cooled in the furnace to obtain the rock salt structure full concentration gradient cathode material.

[0082] In the aforementioned rock salt structure full concentration gradient cathode material, the thickness of the disordered rock salt phase coating layer is 5 nm.

[0083] Example 4

[0084] The only difference between this embodiment and embodiment 1 is that the temperature in step (2) is 300°C, while the other conditions and parameters are exactly the same as in embodiment 1.

[0085] Example 5

[0086] The only difference between this embodiment and embodiment 1 is that the temperature in step (2) is 700°C, while the other conditions and parameters are exactly the same as in embodiment 1.

[0087] Example 6

[0088] The only difference between this embodiment and embodiment 1 is that the heat preservation time in step (2) is 2 hours, while the other conditions and parameters are exactly the same as in embodiment 1.

[0089] Example 7

[0090] The only difference between this embodiment and embodiment 1 is that the heat preservation time in step (2) is 10 hours, while the other conditions and parameters are exactly the same as in embodiment 1.

[0091] Comparative Example 1

[0092] The only difference between this comparative example and Example 1 is that the sintering atmosphere in step (2) is oxygen, while the other conditions and parameters are exactly the same as in Example 1.

[0093] Comparative Example 2

[0094] The only difference between this comparative example and Example 1 is that step (2) is omitted; all other conditions and parameters are exactly the same as in Example 1.

[0095] Comparative Example 3

[0096] The only difference between this comparative example and Example 1 is that step (1) uses a Ni structure designed without a concentration gradient. 0.88 Co 0.06 Mn 0.06 (OH)2, with other conditions and parameters exactly the same as in Example 1.

[0097] Performance testing:

[0098] The high-nickel cathode materials prepared in all the above examples and comparative examples were mixed with SP and PVDF at a mass ratio of 97:1.5:1.5 to prepare a cathode sheet. This sheet was then matched with a lithium metal anode to assemble a lithium-ion battery. The battery was tested at 25°C and a voltage range of 2.5–4.3V. First, it was charged and discharged for 3 cycles at a 0.1C rate, followed by 100 cycles at a 1C rate. The electrochemical performance was then tested, and the results are shown in Table 1.

[0099] Table 1

[0100]

[0101]

[0102] As shown in Table 1, and based on Examples 1-7, the battery made from the rock salt structure full concentration gradient cathode material prepared by the method of the present invention can achieve a first discharge specific capacity of over 191.5 mAh / g at 0.1C, a first discharge specific capacity of over 176.4 mAh / g at 1C, and a capacity retention rate of over 85.6% after 100 cycles. By adjusting the preparation conditions, the battery made from the rock salt structure full concentration gradient cathode material can achieve a first discharge specific capacity of over 198.4 mAh / g at 0.1C, a first discharge specific capacity of over 179.6 mAh / g at 1C, and a capacity retention rate of over 89.2% after 100 cycles.

[0103] A comparison of Examples 1 and 4-5 shows that the temperature of the second sintering treatment affects the performance of the rock salt structure full concentration gradient cathode material described in this invention. Controlling the temperature of the second sintering treatment between 400℃ and 600℃ results in a better performance of the rock salt structure full concentration gradient cathode material. If the temperature of the second sintering treatment is too low, a uniformly distributed rock salt phase cannot be formed on the surface of the high-nickel cathode material, thus failing to provide effective protection for the matrix. If the temperature of the second sintering treatment is too high, it will cause the mixing of lithium and nickel cations to intensify, reducing the electrochemical performance of the cathode material.

[0104] A comparison of Examples 1 and 6-7 shows that the time of the second sintering treatment affects the performance of the rock salt structure full concentration gradient cathode material described in this invention. Controlling the second sintering treatment time to 4-8 hours results in a better performance of the rock salt structure full concentration gradient cathode material. If the second sintering treatment time is too long, a thick rock salt phase will form on the cathode surface, reducing the charge-discharge cycle capacity of the cathode material and hindering lithium-ion transport, thus deteriorating the rate performance. If the second sintering treatment time is too short, a thin and uniform rock salt phase cannot be formed on the cathode material surface, resulting in limited protection for the substrate.

[0105] Comparing Example 1 and Comparative Examples 1-3, it can be seen that the present invention uses a precursor with a full concentration gradient structure, in which the nickel content gradually decreases from the inside to the outside. After lithiation, a secondary sintering is performed in an oxygen-free atmosphere, forming a uniform rock salt phase thin layer on its surface, which can reduce the highly active Ni on the surface of the high-nickel cathode. 4+ Direct contact with the electrolyte reduces interfacial side reactions between the electrolyte and the cathode material, preventing the dissolution of some transition metals. Furthermore, the formation of a thin rock-salt phase layer consumes the surface-unstable Ni. 4+ Lattice oxygen can reduce further oxygen loss from the bulk material and suppress more severe surface reconstruction.

[0106] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a full-concentration-gradient positive electrode material of a rock salt structure, characterized by, The preparation method includes the following steps: (1) The full concentration gradient structure precursor is mixed with a lithium source and subjected to a first sintering treatment in an oxygen-containing atmosphere to obtain a sintered material; (2) The first sintering material is subjected to a second sintering treatment in an oxygen-free atmosphere to obtain the rock salt structure full concentration gradient cathode material; In the full concentration gradient structure precursor, the concentration of nickel decreases in a gradient from the core to the surface; The oxygen-containing atmosphere in step (1) includes any one or a combination of at least two of oxygen, compressed air or nitrogen dioxide. The first sintering treatment includes a first calcination and a second calcination. The temperature of the first calcination is 450℃~550℃ and the time of the first calcination is 2h~6h. The temperature of the second calcination is 700℃~800℃ and the time of the second calcination is 10h~20h. The furnace is cooled after the first sintering treatment. The oxygen-free atmosphere in step (2) includes any one or a combination of at least two of argon, nitrogen, helium or a hydrogen-argon mixture, the temperature of the second sintering treatment is 400℃~600℃, and the time of the second sintering treatment is 4h~8h.

2. The production method according to claim 1, wherein The full-concentration gradient structure precursor described in step (1) is prepared by the following method: A first mixed salt solution is pre-set in a mixing tank. The first mixed salt solution is injected into the mixing tank at a flow rate L1 and the second mixed salt solution is injected into the mixing tank at a flow rate L2. At the same time, the liquid in the mixing tank is injected into the bottom liquid of the reactor along with the precipitant solution and the complexing agent solution at a flow rate L to carry out a co-precipitation reaction, thereby obtaining the full concentration gradient structure cathode precursor.

3. The preparation method according to claim 2, characterized in that, The molar ratio of nickel, cobalt and manganese in the first mixed salt solution is a:b:c, where a is 0.9~1.0, b is 0~0.1, c is 0~0.1, and a+b+c=1.

4. The preparation method according to claim 2, characterized in that, The total molar concentration of metal ions in the first mixed salt solution is 1 mol / L to 3 mol / L.

5. The preparation method according to claim 2, characterized in that, The molar ratio of nickel, cobalt and manganese in the second mixed salt solution is x:y:z, where x is 0.6~0.89, y is 0.11~0.4, z is 0.11~0.4, and x+y+z=1.

6. The preparation method according to claim 2, characterized in that, The total molar concentration of metal ions in the second mixed salt solution is 1.5 mol / L to 2.5 mol / L.

7. The preparation method according to claim 2, characterized in that, With the volume of the mixing tank being 100%, the volume of the first mixed salt solution pre-set in the mixing tank is 20% to 100%.

8. The preparation method according to claim 2, characterized in that, With the volume of the solution required for the coprecipitation reaction being 100%, the volume of the mixing tank is 10% to 100%.

9. The preparation method according to claim 8, characterized in that, With the volume of the solution required for the coprecipitation reaction being 100%, the volume of the mixing tank is 20%~40%.

10. The preparation method according to claim 2, characterized in that, The volume of the reaction apparatus used in the coprecipitation reaction is vL, and the volume of the mixing tank is 0.2vL~1.0vL.

11. The preparation method according to claim 2, characterized in that, The flow rate L1 of the first mixed salt solution is 0.5%vL / h to 1%vL / h.

12. The preparation method according to claim 2, characterized in that, The flow rate L2 of the second mixed salt solution is 1%vL / h to 1.5%vL / h.

13. The preparation method according to claim 2, characterized in that, The flow rate L of the liquid in the mixing tank is 2%vL / h to 3%vL / h.

14. The preparation method according to claim 2, characterized in that, L>L1+L2.

15. The preparation method according to claim 2, characterized in that, The precipitant solution includes any one or a combination of at least two of sodium hydroxide solution, potassium hydroxide solution, or sodium carbonate solution.

16. The preparation method according to claim 2, characterized in that, The mass percentage concentration of the precipitant solution is 10% to 40%.

17. The preparation method according to claim 2, characterized in that, The complexing agent solution includes any one or a combination of at least two of ammonia water, oxalic acid solution, citric acid solution or ammonium bicarbonate solution.

18. The preparation method according to claim 2, characterized in that, The complexing agent solution has a mass percentage concentration of 10% to 40%.

19. The preparation method according to claim 2, characterized in that, The base liquid includes a precipitant, a complexing agent, and water.

20. The preparation method according to claim 2, characterized in that, The pH of the base solution is 11-12.

21. The preparation method according to claim 2, characterized in that, The mass concentration of the complexing agent in the base liquid is 1 g / L to 9 g / L.

22. The preparation method according to claim 2, characterized in that, The temperature for the coprecipitation reaction is 50℃~70℃.

23. The preparation method according to claim 2, characterized in that, The pH of the coprecipitation reaction is 9.5~11.

24. The preparation method according to claim 2, characterized in that, The atmosphere for the coprecipitation reaction is any one or a combination of at least two of nitrogen, argon, or helium.

25. The preparation method according to claim 24, characterized in that, The volume of the reactor is m, and the flow rate of the atmosphere is 0.1 m / h to 4 m / h.

26. The preparation method according to claim 1, characterized in that, The lithium source in step (1) includes any one or a combination of at least two of lithium hydroxide, lithium carbonate, lithium sulfate or lithium phosphate.

27. The preparation method according to claim 1, characterized in that, The molar ratio of the full concentration gradient structure precursor to lithium in the lithium source in step (1) is 1:(1~1.1).

28. A rock salt structure full concentration gradient cathode material, characterized in that, The rock salt structure full concentration gradient cathode material is prepared by the preparation method described in any one of claims 1-27.

29. The rock salt structure full concentration gradient cathode material as described in claim 28, characterized in that, The rock salt structure full concentration gradient cathode material includes a full concentration gradient cathode core and a disordered rock salt phase coating layer disposed on the surface of the full concentration gradient cathode core.

30. The rock salt structure full concentration gradient cathode material as described in claim 29, wherein the thickness of the disordered rock salt phase coating layer is 5 nm to 30 nm.

31. A positive electrode plate, characterized in that, The positive electrode comprises a rock salt structure full concentration gradient positive electrode material as described in any one of claims 28-30.

32. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode as described in claim 31.

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