A lithium supplement additive, its preparation method and application

Abstract

This invention provides a lithium supplement additive, its preparation method, and its application. The lithium supplement additive comprises an M-doped core and a coating layer located on the surface of the core. The coating layer is composed of an oxide of M. The chemical composition of the M-doped core is Li₂Ni. 1‑x M x O2, M is a metallic element in the same period as Ni, 0 < x ≤ 0.5. This invention provides a core-shell lithium-replenishing additive, comprising an M-doped core and a coating layer on the surface of the core. Through bulk doping and surface coating, the prepared lithium-replenishing additive not only suppresses side reactions and stabilizes the material structure, but also reduces the amount of residual alkali on the material surface, thereby reducing gas generation in the battery cell and improving the electrochemical performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery materials, specifically relating to a lithium supplementation additive, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, as a new type of high-energy battery, are widely used in small devices such as mobile communication equipment, portable computers, camcorders, cameras, and MP3 players. They also serve as power storage for solar and wind power generation systems, power sources for cordless power tools, and power sources for hybrid electric vehicles (HEVs) and pure electric vehicles (EVs). In particular, with the rapid growth in demand for lithium-ion batteries from electric vehicles and solar and wind energy storage, high requirements are being placed on the safety, cycle performance, rate performance, and high and low temperature performance of lithium-ion batteries.

[0003] To meet the design requirements of high-energy-density batteries, the most effective approach is to select high-capacity positive and negative electrode materials, such as silicon, tin, aluminum, and oxides as novel negative electrode materials. However, during the first charge of a lithium battery, some of the lithium released from the positive electrode forms an irreversible lithium-containing passivation film (SEI) on the surface of the negative electrode, resulting in the loss of active lithium and thus reducing the battery's usable energy.

[0004] To compensate for this lithium loss, the current approach is to pre-replenish lithium on either the positive or negative electrode. Negative electrode lithium replenishment typically involves reacting lithium metal powder, foil, or sheets with the negative electrode material. However, this method suffers from poor chemical stability of the lithiation reagent and significant safety hazards associated with highly reactive lithium powder. Positive electrode lithium replenishment generally involves mixing the replenishing material with the positive electrode material in a specific ratio, preparing a slurry, and then forming a battery cell. During the initial charging process, excess lithium is released to replenish the lithium consumed in forming the SEI film on the negative electrode surface, thus completing the lithium replenishment. Compared to negative electrode lithium replenishment, positive electrode lithium replenishment technology does not require changes to existing battery manufacturing processes, thus offering advantages such as lower cost, simplicity, and higher safety, making it more promising for industrial applications.

[0005] A significant problem with existing lithium-ion additives in batteries is that they cause cell volume expansion and increased gas production during high-temperature storage or cycling, affecting battery cycle stability and posing certain safety hazards. The gas production issue primarily stems from high levels of residual alkali on the surface of the lithium-ion additive and its strong oxidizing properties under high voltage, leading to electrolyte side reactions.

[0006] Therefore, how to reduce gas production and improve the electrochemical performance of batteries is a technical problem that urgently needs to be solved. Summary of the Invention

[0007] In view of the deficiencies existing in the prior art, the purpose of the present invention is to provide a lithium-supplementing additive, and a preparation method and application thereof. The present invention provides a lithium-supplementing additive with a core-shell structure, comprising an M-doped inner core and a coating layer located on the surface of the inner core. Through bulk doping and surface coating, the prepared lithium-supplementing additive can not only inhibit side reactions and stabilize the material structure, but also reduce the amount of residual alkali on the material surface, thereby reducing gas generation in the electric core and improving the electrochemical performance of the battery.

[0008] To achieve the purpose of the invention, the present invention adopts the following technical scheme:

[0009] In a first aspect, the present invention provides a lithium-supplementing additive, the lithium-supplementing additive comprising an M-doped inner core and a coating layer located on the surface of the inner core, and the composition of the coating layer is an oxide of M;

[0010] The chemical composition of the M-doped inner core is Li₂Ni 1-x M x ₓO₂, M is a metal element in the same period as Ni, 0 < x < 1, for example, x can be 0.0001, 0.001, 0.002, 0.005, 0.007, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4 or 0.5, etc.

[0011] In the present invention, a lithium-supplementing additive with a core-shell structure is provided, comprising an M-doped inner core and a coating layer located on the surface of the inner core. M is selected from elements in the same period as Ni, and the atomic radius of M is close to that of Ni, so doping M can maintain the framework of Li₂NiO₂ itself, so that the structure can be more stable during the bonding process. Moreover, doping M can also improve the utilization rate of lithium salt to a certain extent, the prepared Li₂NiO₂ has higher purity, and the residual alkali value is also reduced. Meanwhile, doping M element can bring certain lattice energy, which has positive effects on improving the conductivity of the material, the stability against metal dissolution, and increasing the capacity. In addition, using the oxide of M as the coating layer on the surface of the inner core can effectively reduce the residual alkali value of the lithium-supplementing additive, alleviate the damage of OH⁻ in the residual alkali to the binder during the preparation of the positive electrode, and achieve the effect of improving the quality of the positive electrode sheet. Therefore, through bulk doping and surface coating, the prepared lithium-supplementing additive can not only inhibit side reactions and stabilize the material structure, but also reduce the amount of residual alkali on the material surface, thereby reducing gas generation in the electric core and improving the electrochemical performance of the battery.

[0012] In the present invention, the doping amount of M is lower than the content of Ni, because excessive doping will destroy the framework of Li₂NiO₂ itself, thereby affecting the cycling stability of the battery.

[0013] Preferably, M is selected from at least one of Co, Fe, Mn, Ti, Mg, V, Cu and Mo.

[0014] In this invention, metal M is selected from elements in the same period as Ni, and its radius is close to that of Ni. Therefore, the incorporation of M can maintain the framework of the core Li2NiO2 of the lithium supplementation additive, thereby making the structure more stable during the bonding process.

[0015] Preferably, x is 0.002-0.01, and more preferably 0.004-0.008.

[0016] In this invention, the amount of metal M incorporated has a significant impact on the structure and performance of the lithium supplement additive. When x is too large, that is, when the content of metal M is too high, it will affect the main structure of the lithium supplement additive (i.e., the structure of LiNiO2), causing the structure to collapse during battery cycling and affecting the electrochemical performance of the battery. When x is too small, the advantages brought by doping cannot be effectively realized due to the insufficient amount of metal M incorporated.

[0017] Preferably, with the total mass of the main elements in the core being 100%, and the main elements being Li, Ni, and O, the content of the coating layer is 0.3-4%.

[0018] In this invention, the main body composed of the main elements Li, Ni and O can be considered as the matrix, M is doped in the matrix to form a core, and a coating layer is coated on the surface of the core to form a shell.

[0019] In this invention, when the content of the coating layer is too small, it cannot effectively isolate the side reaction of the material surface being eroded by the electrolyte. When the content of the coating layer is too large, it will affect the migration of lithium ions, thereby reducing the capacity and deteriorating the electrochemical performance.

[0020] Preferably, the oxide of M includes at least one of cobalt tetroxide, ferric oxide, manganese dioxide, titanium dioxide, magnesium oxide, vanadium pentoxide, cuprous oxide, and molybdenum dioxide.

[0021] In a second aspect, the present invention provides a method for preparing a lithium supplementation additive as described in the first aspect, the method comprising:

[0022] The lithium-supplementing additive is obtained by dry ball milling and sintering of Li2NiO2 and the oxide of M.

[0023] The sintering temperature is greater than or equal to 600℃, for example, it can be 600℃, 650℃, 700℃, 750℃ or 800℃, etc.

[0024] In this invention, the mechanical force during ball milling allows a portion of the metal oxide (M) to be incorporated into the Li₂NiO₂ matrix. High-temperature sintering then promotes the inward diffusion of the incorporated M into the Li₂NiO₂ matrix, creating a uniform doping effect. Simultaneously, it repairs the structural damage caused by ball milling. Under high-temperature sintering conditions, the remaining dopant that was not incorporated into the Li₂NiO₂ matrix core forms a coating layer of metal oxide (M) on the outer surface of the doped matrix, achieving a coating effect. This method reduces the residual alkali content on the surface of the lithium-ion additive through both doping and coating, thereby reducing gas generation in the battery cell and improving the battery's electrochemical performance.

[0025] In this invention, the doping effect produced by ball milling is limited, confined to the near surface, and the doping effect is poor. When the sintering temperature is too low, it cannot effectively improve the bulk phase incorporation effect, and the structural damage caused by ball milling is difficult to repair.

[0026] Preferably, the particle size D50 of the oxide of M is less than 50 nm, for example, it can be 10 nm, 20 nm, 30 nm, 40 nm or 50 nm.

[0027] In this invention, when the particle size of the oxide of M is too large, the oxide of M cannot be effectively doped into the crystal lattice and cannot achieve a coating effect.

[0028] Preferably, the amount of oxide of M added accounts for 0.5-5% of the mass of Li2NiO2, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.

[0029] In this invention, the amount of oxide added to M is partly used for bulk doping and partly for surface coating. If the amount added is too large, it will affect the structure of Li2NiO2, reducing its stability and impacting battery performance. If the amount added is too small, it will not effectively achieve the bulk doping effect, and the coating effect will be even worse. Preferably, the Li2NiO2 is prepared by the following method, which includes:

[0030] Lithium salt and nickel salt were stirred and mixed in a solvent to obtain a mixture, which was then dried and calcined to obtain Li2NiO2.

[0031] This invention does not limit the drying method. For example, drying can be done by blowing air, vacuum drying, or spray drying.

[0032] Preferably, the lithium salt includes at least one of lithium oxide, lithium carbonate, lithium hydroxide, lithium fluoride, lithium phosphate, and lithium dihydrogen phosphate.

[0033] Preferably, the lithium salt has a particle size D50 of 5-50 μm, where D50 is the median particle size, such as 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm.

[0034] Preferably, the nickel salt includes at least one of nickel suboxide, nickel trioxide, nickel dioxide, nickel hydroxide, nickel hydroxide oxide, nickel carbonate, nickel oxalate, and nickel acetate.

[0035] Preferably, the particle size D50 of the nickel salt is 5-50 μm, for example, it can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm, etc.

[0036] Preferably, the molar ratio of the lithium salt to the nickel salt is (1.9-2.2):1, for example, it can be 1.9:1, 2.0:1, 2.1:1 or 2.2:1, etc.

[0037] Preferably, the solvent includes at least one of water, ethanol, and acetone.

[0038] Preferably, the solid content in the mixture is 15-60%, for example, it can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% or 60%, etc.

[0039] Preferably, the calcination temperature is 600-770℃, for example, it can be 600℃, 630℃, 660℃, 690℃, 720℃, 750℃, or 770℃. Preferably, the calcination heating rate is 2-10℃ / min, for example, it can be 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min.

[0040] Preferably, the calcination time is 10-20 hours, for example, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, or 20 hours.

[0041] Preferably, during the ball milling process, the mass ratio of the grinding balls to the mixture of lithium supplementation additive and metal oxide is (10-20):1, for example, it can be 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1 or 20:1, etc.

[0042] In this invention, the mass ratio of the grinding balls to the mixture of lithium-supplementing additives and metal oxides is the ball-to-material ratio.

[0043] Preferably, the rotational speed of the ball mill is 200-650 rpm, for example, it can be 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm or 650 rpm, etc., preferably 400-650 rpm.

[0044] In this invention, if the ball milling speed is too high, it will cause agglomeration and break the bulk structure of Li2NiO2. If the ball milling speed is too low, the energy will be too low to achieve the mechanical ball milling effect and bulk doping will not be achieved.

[0045] Preferably, the ball milling time is 30-480 min, such as 30 min, 60 min, 120 min, 180 min, 240 min, 300 min, 360 min, 420 min or 480 min, etc., and more preferably 240-480 min.

[0046] In this invention, if the ball milling time is too long, the milled material will stick together and clump together, destroying the bulk structure of Li2NiO2. If the ball milling time is too short, high-energy milling cannot be achieved, and the bulk doping effect cannot be achieved.

[0047] Preferably, the atmosphere used in the ball mill is an inert atmosphere.

[0048] The present invention does not limit the inert atmosphere. For example, the inert atmosphere can be an inert gas, including at least one of argon and nitrogen, or a gas composed of an inert gas and a small amount of oxygen, wherein the oxygen partial pressure is <200ppm.

[0049] Preferably, the sintering temperature is 600-770℃, for example, it can be 600℃, 630℃, 660℃, 690℃, 720℃, 750℃ or 770℃, etc.

[0050] In this invention, the sintering temperature has a significant impact on the bulk doping effect. When the sintering temperature is too low, there is only mixing and no mutual diffusion can occur to achieve bulk doping. However, when the sintering temperature is too high, the Li2NiO2 matrix structure is destroyed and the material decomposes and fails.

[0051] Preferably, the heating rate of the sintering is 2-10℃ / min, for example, it can be 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, etc.

[0052] Preferably, the sintering time is 10-20 hours, for example, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, or 20 hours.

[0053] As a preferred embodiment of the present invention, the preparation method of the lithium supplementation additive includes the following steps:

[0054] (I) Lithium salt and nickel salt with a molar ratio of (1.9-2.2):1 are stirred and mixed in a solvent to obtain a mixture with a solid content of 15-60%;

[0055] (II) Dry the mixture described in step (I) and calcine it in an inert atmosphere for 10-20 hours at a temperature of 600-770℃ to obtain Li2NiO2;

[0056] (III) Dry ball milling of Li2NiO2 and the oxide of M at a speed of 200-650 rpm for 30-480 min in an inert atmosphere to obtain a mixed product, wherein the mass ratio of the grinding ball to the mixture of lithium supplementation additive and metal oxide is (10-20):1.

[0057] (IV) The mixed product described in step (III) is sintered at 600-770°C for 10-20 h to obtain the lithium supplementation additive.

[0058] In this invention, the inert atmosphere described in steps (II) and (III) is the same.

[0059] Thirdly, the present invention provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery includes the lithium-replenishing additive as described in the first aspect.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] This invention provides a core-shell lithium-replenishing additive, comprising an M-doped core and a coating layer on the surface of the core. Through bulk doping and surface coating, the prepared lithium-replenishing additive not only suppresses side reactions and stabilizes the material structure, but also reduces the amount of residual alkali on the material surface, thereby reducing gas generation in the battery cell and improving the electrochemical performance of the battery. Attached Figure Description

[0062] Figure 1 The image shows a SEM image of the lithium-adding additive provided in Comparative Example 5, which was not subjected to bulk doping and surface coating.

[0063] Figure 2 SEM images of the lithium-replenishing additives after bulk doping and surface coating provided in Example 1. Detailed Implementation

[0064] 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.

[0065] Example 1

[0066] This embodiment provides a lithium supplement additive, comprising a Co-doped Li₂NiO₂ core and a Co₃O₄ coating layer on the surface of the core, wherein the chemical composition of the core is Li₂NiO₂. 0.994 Co 0.006 O2.

[0067] In this lithium supplement additive, the content of the coating layer Co3O4 accounts for 2.4% of the total mass of the main elements Li, Ni and O.

[0068] (1) Lithium oxide (D50 of 30 μm) and nickel oxide (D50 of 25 μm) in a molar ratio of 2:1 were stirred and mixed in water to obtain a mixture with a solid content of 40%.

[0069] (2) The mixture in step (1) is dried and heated to 685°C at a rate of 6°C / min and then calcined for 15 h to obtain Li2NiO2;

[0070] (3) Li2NiO2 and Co3O4 (the amount of Co3O4 added accounts for 3% of Li2NiO2, and the particle size D50 of Co3O4 is 25nm) are dry ball-milled in an argon atmosphere at a speed of 450rpm for 240min to obtain a mixed product, wherein the ball-to-material ratio is (10-20):1.

[0071] (4) The mixed product from step (3) is sintered at 685°C for 15 hours at a heating rate of 6°C / min to obtain the lithium supplementation additive.

[0072] Figure 2 The SEM image of the lithium supplementation additive provided in this embodiment is shown. As can be seen from the image, the particle surface has a uniformly distributed coating.

[0073] Example 2

[0074] This embodiment provides a lithium supplement additive, comprising an Fe-doped Li₂NiO₂ core and a Fe₂O₃ coating layer on the surface of the core, wherein the chemical composition of the core is Li₂NiO₂. 0.996 Fe 0.004 O2.

[0075] In this lithium supplement additive, the Fe2O3 coating layer accounts for 1.6% of the total mass of the main elements Li, Ni and O.

[0076] (1) Lithium carbonate (D50 of 25 μm) and nickel oxide (D50 of 30 μm) with a molar ratio of 2.1:1 were stirred and mixed in ethanol to obtain a mixture with a solid content of 35%.

[0077] (2) The mixture in step (1) is dried and heated to 730°C at a rate of 4°C / min and then calcined for 13 hours to obtain Li2NiO2;

[0078] (3) Li2NiO2 and Fe2O3 (Fe2O3 accounts for 2% of Li2NiO2 and the particle size D50 of Fe2O3 is 20nm) were dry ball-milled in nitrogen at 350rpm for 120min to obtain a mixed product, wherein the ball-to-material ratio was (10-20):1.

[0079] (4) The mixed product from step (3) is sintered at 730°C for 13 hours at a heating rate of 4°C / min to obtain the lithium supplementation additive.

[0080] Example 3

[0081] This embodiment provides a lithium supplement additive, comprising a Mn-doped Li₂NiO₂ core and a MnO₂ coating layer on the surface of the core, wherein the core has a chemical composition of Li₂NiO₂. 0.992 Mn 0.008 O2.

[0082] In this lithium supplement additive, the content of the coating layer MnO2 accounts for 2.22% of the total mass of the main elements Li, Ni and O.

[0083] (1) Lithium hydroxide (D50 of 35 μm) and nickel hydroxide (D50 of 35 μm) in a molar ratio of 1.9:1 were stirred and mixed in acetone to obtain a mixture with a solid content of 45%.

[0084] (2) The mixture in step (1) is dried and heated to 640°C at a rate of 6°C / min and then calcined for 18h to obtain Li2NiO2;

[0085] (3) Li2NiO2 and MnO2 (MnO2 accounts for 3% of Li2NiO2 and the particle size D50 of MnO2 is 30nm) are dry ball-milled at 500rpm for 360min in a mixture of nitrogen and oxygen (oxygen partial pressure is 180ppm) to obtain a mixed product, wherein the ball-to-material ratio is (10-20):1;

[0086] (4) The mixed product from step (3) is sintered at 640°C for 18 hours at a heating rate of 6°C / min to obtain the lithium supplementation additive.

[0087] Example 4

[0088] This embodiment provides a lithium supplement additive, comprising a Ti-doped Li₂NiO₂ core and a TiO₂ coating layer on the surface of the core, wherein the core has a chemical composition of Li₂NiO₂. 0.99 Ti0.01 O2.

[0089] In this lithium supplement additive, the content of the coating layer TiO2 accounts for 4% of the total mass of the main elements Li, Ni and O.

[0090] (1) Lithium fluoride (D50 of 5 μm) and nickel carbonate (D50 of 5 μm) with a molar ratio of 2.2:1 were stirred and mixed in ethanol to obtain a mixture with a solid content of 15%.

[0091] (2) The mixture in step (1) is dried and heated to 600°C at a rate of 2°C / min and then calcined for 20h to obtain Li2NiO2;

[0092] (3) Li2NiO2 and TiO2 (the amount of TiO2 added accounts for 5% of Li2NiO2, and the particle size D50 of TiO2 is 10nm) are dry ball-milled at 200rpm for 480min in a mixture of argon and oxygen (oxygen partial pressure is 180ppm) to obtain a mixed product, wherein the ball-to-material ratio is (10-20):1;

[0093] (4) The mixed product from step (3) is sintered at 600°C for 20 hours at a heating rate of 2°C / min to obtain the lithium supplementation additive.

[0094] Example 5

[0095] This embodiment provides a lithium supplement additive, comprising a Mg-doped Li₂NiO₂ core and a MgO coating layer on the surface of the core, wherein the chemical composition of the core is Li₂NiO₂. 0.998 Mg 0.002 O2.

[0096] In this lithium supplement additive, the content of the MgO coating layer accounts for 0.3% of the total mass of the main elements Li, Ni and O.

[0097] (1) Lithium phosphate (D50 is 50 μm) and nickel oxalate (D50 is 50 μm) with a molar ratio of 2:1 were stirred and mixed in acetone to obtain a mixture with a solid content of 60%.

[0098] (2) The mixture described in step (1) is dried and heated to 770°C at a rate of 10°C / min and then calcined for 10 h to obtain Li2NiO2;

[0099] (3) Li2NiO2 and MgO (MgO is added at 0.5% of Li2NiO2 and the particle size D50 of MgO is 40nm) are dry ball-milled at 650rpm for 30min in a mixture of nitrogen and oxygen (oxygen partial pressure is 100ppm) to obtain a mixed product, wherein the ball-to-material ratio is (10-20):1.

[0100] (4) The mixed product described in step (3) is sintered at 770°C for 10 h with a heating rate of 10°C / min to obtain the lithium supplementation additive.

[0101] Example 6

[0102] The difference between this embodiment and Embodiment 1 is that the chemical composition of the core is Li2Ni. 0.999 Co 0.001 O2.

[0103] The remaining preparation methods and parameters are consistent with those in Example 1.

[0104] Example 7

[0105] The difference between this embodiment and Embodiment 1 is that the chemical composition of the core is Li2Ni. 0.98 Co 0.02 O2.

[0106] The remaining preparation methods and parameters are consistent with those in Example 1.

[0107] Example 8

[0108] The difference between this embodiment and Embodiment 1 is that the content of Co3O4 in the coating layer is 0.2%.

[0109] The remaining preparation methods and parameters are consistent with those in Example 1.

[0110] Example 9

[0111] The difference between this embodiment and Embodiment 1 is that the content of Co3O4 in the coating layer is 5%.

[0112] The remaining preparation methods and parameters are consistent with those in Example 1.

[0113] Example 10

[0114] The difference between this embodiment and Embodiment 1 is that the particle size D50 of Co3O4 is 60 nm.

[0115] The remaining preparation methods and parameters are consistent with those in Example 1.

[0116] Example 11

[0117] The difference between this embodiment and embodiment 1 is that the sintering temperature in step (4) is 550°C.

[0118] The remaining preparation methods and parameters are consistent with those in Example 1.

[0119] Example 12

[0120] The difference between this embodiment and embodiment 1 is that the sintering temperature in step (4) is 800°C.

[0121] The remaining preparation methods and parameters are consistent with those in Example 1.

[0122] Example 13

[0123] The difference between this embodiment and embodiment 1 is that the ball milling speed in step (3) is 150 rpm.

[0124] The remaining preparation methods and parameters are consistent with those in Example 1.

[0125] Example 14

[0126] The difference between this embodiment and embodiment 1 is that the ball milling speed in step (3) is 700 rpm.

[0127] The remaining preparation methods and parameters are consistent with those in Example 1.

[0128] Example 15

[0129] The difference between this embodiment and embodiment 1 is that the ball milling time in step (3) is 20 minutes.

[0130] The remaining preparation methods and parameters are consistent with those in Example 1.

[0131] Example 16

[0132] The difference between this embodiment and embodiment 1 is that the ball milling time in step (3) is 510 min.

[0133] The remaining preparation methods and parameters are consistent with those in Example 1.

[0134] Comparative Example 1

[0135] The difference between this comparative example and Example 1 is that the sintering temperature is 300°C.

[0136] The remaining preparation methods and parameters are consistent with those in Example 1.

[0137] Comparative Example 2

[0138] The difference between this comparative example and Example 1 is that Zr doping is used instead of Co doping, and the coating layer is ZrO2.

[0139] The remaining preparation methods and parameters are consistent with those in Example 1.

[0140] Comparative Example 3

[0141] The difference between this comparative example and Example 1 is that step (3) is not ball milled, and Li2NiO2 and Co3O4 are directly sintered after being mixed in an argon atmosphere.

[0142] The remaining preparation methods and parameters are consistent with those in Example 1.

[0143] Comparative Example 4

[0144] The difference between this comparative example and Example 1 is that the total amount of Co3O4 added accounts for 0.2% of Li2NiO2.

[0145] The remaining preparation methods and parameters are consistent with those in Example 1.

[0146] Comparative Example 5

[0147] The difference between this comparative example and Example 1 is that steps (3) and (4) are not performed.

[0148] The remaining preparation methods and parameters are consistent with those in Example 1.

[0149] Figure 1 The SEM image of the lithium supplementation additive provided in this comparative example is shown.

[0150] Performance testing:

[0151] The lithium-replenishing additives provided in Examples 1-16 and Comparative Examples 1-5 were used in conjunction with the cathode material. The cathode material to be tested, lithium iron phosphate (using lithium iron phosphate as an example; other cathode materials such as ternary cathode materials, lithium cobalt oxide, and other common cathode systems all have the same gain effect), lithium-replenishing material, binder (PVDF), and conductive agent SP were mixed at a mass ratio of 93:2:2.5:2.5. Dispersant N-methylpyrrolidone (NMP) was added to form a slurry, which was then uniformly coated onto aluminum foil. After drying, the slurry was pressed into sheets, punched, and dried in a drying oven at 80°C for 12 hours before use. Using a lithium metal sheet as the counter electrode, a 1 mol / L LiPF6 electrolyte was used. The solvent was a three-component mixed solvent, i.e., a mixture of EC:DMC:EMC with a volume ratio of 1:1:1. A Celgard 2400 microporous polypropylene membrane was used as the separator. CR2032 coin cells were assembled in an argon glove box in Micronesia. The charge and discharge tests of the button cells were conducted on the Blue Battery Testing System, with a charge and discharge voltage of 2.0-3.8V and a charge and discharge rate of 1C.

[0152] The test results are shown in Table 1.

[0153] Table 1

[0154]

[0155]

[0156] analyze:

[0157] A comparison of the data results from Examples 1 with those from Examples 6 and 7 shows that both excessive and insufficient doping amounts result in a higher residual alkali value, a weak improvement in gas production in the cell, a decrease in first-cycle efficiency, and a reduction in capacity retention. This indicates that insufficient doping amounts are ineffective, while excessive doping amounts can affect the structure of the substrate, impacting the first-cycle efficiency and cycle stability of the battery.

[0158] A comparison of the data results from Examples 1 with Examples 8 and 9 shows that both excessively high and low coating content weaken the effect of reducing residual alkali, making it difficult to effectively reduce gas production in the cell, and also reducing the battery's first-week efficiency and capacity retention. This is because when the coating content is too low, it cannot effectively isolate the side reaction of electrolyte erosion on the material surface, while when the coating content is too high, it will affect the migration of lithium ions, thereby reducing the battery's capacity retention and first-week efficiency.

[0159] A comparison of the data results from Example 1 and Example 10 shows that when the added oxide particle size is too large, it is difficult to effectively dope into the crystal lattice and cannot achieve a coating effect, resulting in a high residual alkali value, making it difficult to reduce gas generation in the cell, and reducing both capacity retention and first-cycle efficiency.

[0160] A comparison of the data results from Example 1 with those from Examples 11 and 12 shows that when the sintering temperature is too low, ball milling can only be limited to surface doping and cannot achieve a good bulk doping effect. Therefore, the residual alkali value is high, making it difficult to reduce gas production in the cell. The capacity retention rate and the first-cycle efficiency of the battery also show a downward trend. When the sintering temperature is too high, the Li2NiO2 matrix structure is destroyed, the material decomposes and fails, and the battery fails.

[0161] A comparison of the data results from Examples 1 and 13-16 shows that excessive ball milling time and speed cause material agglomeration, damaging the bulk structure of Li2NiO2, leading to an increase in residual alkali value, failure to reduce gas production in the cell, and a decrease in capacity retention and first-cycle efficiency. Conversely, insufficient ball milling time and speed fail to achieve high-energy grinding, negating the bulk doping effect. Consequently, the resulting battery exhibits a high residual alkali value, increased gas production, and a decreasing trend in both capacity retention and first-cycle efficiency.

[0162] A comparison of the data results of Example 1 and Comparative Example 1 shows that the residual alkali value increased significantly, indicating that the gas generation in the cell was not improved and the side reaction with the electrolyte was not suppressed. The first-cycle efficiency and capacity retention rate were also significantly reduced. This is because when the sintering temperature is too low, the oxides of M cannot diffuse into each other, so it is difficult to achieve bulk doping and it does not have the desired effect.

[0163] A comparison of the data results of Example 1 and Comparative Example 2 shows that doping with elements not in the same period as Ni will have an adverse effect on the performance of the battery. Not only will it fail to effectively reduce the residual alkali value and reduce gas production, but it will also have a negative impact on the battery's first-cycle efficiency and capacity retention.

[0164] A comparison of the data results of Example 1 and Comparative Example 3 shows that without ball milling, it is difficult to achieve the effect of bulk doping, thus failing to reduce the residual alkali on the material surface, resulting in a significant reduction in the first-cycle efficiency and capacity retention of the battery.

[0165] A comparison of the data results of Example 1 and Comparative Example 4 shows that the raw material of M oxide is too small, making it difficult for bulk doping and surface coating to have a significant effect, thus having little impact on the improvement of residual alkali on the material surface, the first cycle efficiency of the battery, and the capacity retention rate.

[0166] A comparison of the data results of Example 1 and Comparative Example 5 shows that without bulk doping and surface coating, the residual alkali of the material cannot be reduced, and the first-cycle efficiency and capacity retention of the battery cannot be significantly improved.

[0167] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A lithium supplement additive, characterized in that, The lithium supplementation additive includes an M-doped core and a coating layer located on the surface of the core, wherein the coating layer is composed of an oxide of M; The chemical composition of the M-doped core is Li₂Ni. 1-x M x O2, M is a metallic element in the same period as Ni, and x is 0.002-0.01; M is selected from at least one of Co, Fe, Mn, Ti, Mg, V, Cu and Mo; The lithium supplementary additive is prepared by the following method, which includes the following steps: The lithium-supplementing additive is obtained by dry ball milling and sintering of Li2NiO2 and the oxide of M. Wherein, the particle size D50 of the oxide of M is less than 50 nm, the amount of oxide of M added accounts for 0.5-5% of the mass of Li2NiO2, the ball milling speed is 200-650 rpm, the ball milling time is 30-480 min, and the sintering temperature is greater than or equal to 600℃.

2. The lithium supplement additive according to claim 1, characterized in that, x is between 0.004 and 0.

008.

3. The lithium supplement additive according to claim 1, characterized in that, With the total mass of the main elements in the core being 100%, the main elements being Li, Ni and O, and the content of the coating layer being 0.3-4%.

4. The lithium supplement additive according to claim 1, characterized in that, The oxide of M includes at least one of cobalt tetroxide, ferric oxide, manganese dioxide, titanium dioxide, magnesium oxide, vanadium pentoxide, cuprous oxide, and molybdenum dioxide.

5. A method for preparing a lithium supplement additive as described in any one of claims 1-4, characterized in that, The preparation method includes: The lithium-supplementing additive is obtained by dry ball milling and sintering of Li2NiO2 and the oxide of M. Wherein, the particle size D50 of the oxide of M is less than 50 nm, the amount of oxide of M added accounts for 0.5-5% of the mass of Li2NiO2, the ball milling speed is 200-650 rpm, and the ball milling time is 30-480 min; The sintering temperature is greater than or equal to 600℃.

6. The preparation method according to claim 5, characterized in that, The Li2NiO2 is prepared by the following method, the method comprising: Lithium salt and nickel salt were stirred and mixed in a solvent to obtain a mixture, which was then dried and calcined to obtain Li2NiO2.

7. The preparation method according to claim 6, characterized in that, The lithium salt includes at least one of lithium oxide, lithium carbonate, lithium hydroxide, lithium fluoride, lithium phosphate, and lithium dihydrogen phosphate.

8. The preparation method according to claim 6, characterized in that, The lithium salt has a particle size D50 of 5-50 μm.

9. The preparation method according to claim 6, characterized in that, The nickel salt includes at least one of nickel suboxide, nickel trioxide, nickel dioxide, nickel hydroxide, nickel hydroxide oxide, nickel carbonate, nickel oxalate, and nickel acetate.

10. The preparation method according to claim 6, characterized in that, The particle size D50 of the nickel salt is 5-50 μm.

11. The preparation method according to claim 6, characterized in that, The molar ratio of the lithium salt to the nickel salt is (1.9-2.2):

1.

12. The preparation method according to claim 6, characterized in that, The solvent includes at least one of water, ethanol, and acetone.

13. The preparation method according to claim 6, characterized in that, The solid content in the mixture is 15-60%.

14. The preparation method according to claim 6, characterized in that, The calcination temperature is 600-770℃.

15. The preparation method according to claim 6, characterized in that, The heating rate for calcination is 2-10℃ / min.

16. The preparation method according to claim 6, characterized in that, The calcination time is 10-20 hours.

17. The preparation method according to claim 5, characterized in that, During the ball milling process, the mass ratio of the grinding balls to the mixture of lithium supplementation additives and metal oxides is (10-20):

1.

18. The preparation method according to claim 5, characterized in that, The ball mill rotates at a speed of 400-650 rpm.

19. The preparation method according to claim 5, characterized in that, The ball milling time is 240-480 min.

20. The preparation method according to claim 5, characterized in that, The atmosphere used in the ball mill is an inert atmosphere.

21. The preparation method according to claim 5, characterized in that, The sintering temperature is 600-770℃.

22. The preparation method according to claim 5, characterized in that, The heating rate for sintering is 2-10℃ / min.

23. The preparation method according to claim 5, characterized in that, The sintering time is 10-20 hours.

24. The preparation method according to claim 5, characterized in that, The preparation method of the lithium supplement additive includes the following steps: (I) Lithium salt and nickel salt with a molar ratio of (1.9-2.2):1 are stirred and mixed in a solvent to obtain a mixture with a solid content of 15-60%; (II) The mixture described in step (I) is dried and calcined in an inert atmosphere for 10-20 h at a temperature of 600-770 °C to obtain Li2NiO2; (III) Dry ball milling of Li2NiO2 and the oxide of M at a speed of 200-650 rpm for 30-480 min in an inert atmosphere to obtain a mixed product, wherein the mass ratio of the grinding ball to the mixture of lithium supplementation additive and metal oxide is (10-20):

1. (IV) The mixed product described in step (III) is sintered at 600-770°C for 10-20 h to obtain the lithium supplementation additive.

25. A lithium-ion battery, characterized in that, The positive electrode of the lithium-ion battery includes the lithium replenishing additive as described in any one of claims 1-4.

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