Composite lithium supplement, preparation method thereof and lithium ion battery

Abstract

The application provides a composite lithium supplementing agent, a preparation method thereof and a lithium ion battery. The composite lithium supplementing agent comprises a core, an intermediate layer and a shell layer. The intermediate layer is coated on the surface of the core, and the shell layer is coated on the surface of the intermediate layer away from the core. The core comprises lithium-rich lithium titanium manganese oxide, the intermediate layer comprises lithium-rich lithium nickelate, and the shell layer comprises lithium oxalate and / or lithium squarate. The composite lithium supplementing agent has the lithium-rich lithium titanium manganese oxide as the core, the lithium-rich lithium nickelate as the intermediate layer, and the organic lithium salt as the shell layer. The lithium-rich lithium nickelate compensates for the low lithium supplementing capacity of the lithium-rich lithium titanium manganese oxide. The shell layer improves the air stability of the lithium supplementing agent, reduces the residual alkali on the surface of the lithium supplementing agent, and catalyzes the Li + release of the shell layer, thereby improving the lithium supplementing capacity, and a composite lithium supplementing agent with high lithium supplementing capacity, low gas production and low residual alkali is constructed.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a composite lithium replenishing agent, its preparation method, and lithium-ion batteries. Background Technology

[0002] Cathode lithium replenishment agents are key materials in lithium-ion battery pre-lithiation technology. Their core significance lies in compensating for irreversible lithium loss during the initial charge-discharge process of lithium-ion batteries, thereby addressing core performance pain points such as energy density, initial efficiency, and cycle stability. Commonly used cathode lithium replenishment agents include lithium-rich nickel oxide, lithium-rich manganese-based oxide, lithium metal, and lithium nitrides. Among these, lithium-rich manganese-based oxide has a relatively low theoretical capacity and poor conductivity, resulting in limited lithium replenishment capacity. Lithium-rich nickel oxide features high lithium replenishment capacity, with a theoretical delithiation capacity reaching 521 mAh / g. It also possesses advantages such as moderate delithiation potential and good compatibility with cathode materials, effectively compensating for the battery's initial irreversible lithium loss. However, lithium-rich nickel oxide suffers from drawbacks such as high surface residual lithium, poor air stability, hygroscopicity, and susceptibility to side reactions with the electrolyte. Therefore, existing single lithium replenishment agents exhibit one or more technical defects, including high surface residual lithium, poor air stability, and low delithiation capacity. Summary of the Invention

[0003] The purpose of this invention is to provide a composite lithium replenishing agent, its preparation method, and a lithium-ion battery. The composite lithium replenishing agent uses lithium-rich lithium manganese titanium oxide as the core, lithium-rich lithium nickel oxide as the intermediate layer, and an organic lithium salt as the outer shell layer. The lithium-rich lithium nickel oxide can compensate for the low lithium replenishing capacity of lithium-rich lithium manganese titanium oxide. The outer shell layer improves the air stability of the lithium replenishing agent and reduces residual alkali on the surface of the lithium replenishing agent. Meanwhile, the lithium-rich lithium nickel oxide reacts with the outer shell layer, catalyzing its Li-ionization process. + This process releases and enhances lithium replenishment capacity, thus creating a composite lithium replenishing agent with high lithium replenishment capacity, low gas production, and low residual alkali.

[0004] To achieve this objective, the present invention adopts the following technical solution:

[0005] In a first aspect, the present invention provides a composite lithium replenishing agent, the composite lithium replenishing agent comprising a core, an intermediate layer and an outer shell layer, wherein the intermediate layer covers the surface of the core, and the outer shell layer covers the surface of the intermediate layer away from the core;

[0006] The core comprises lithium-rich lithium manganese titanate, the intermediate layer comprises lithium-rich lithium nickelate, and the outer shell layer comprises lithium oxalate and / or lithium squartzate.

[0007] This invention uses lithium-rich lithium manganese titanate as the core, Ti 4+While lithium-rich lithium titanium manganese oxide (LNO) can suppress oxygen evolution and phase transition, and exhibits low high-pressure gas production, its theoretical capacity is relatively low, and its electronic conductivity is poor, resulting in low lithium replenishment capacity. To address these issues, lithium-rich lithium nickel oxide (LNO) is used as an intermediate layer. LNO possesses strong Ni-O covalent bonds, which can suppress Mn migration in LNO, further enhancing structural stability, reducing gas production, and improving the material's electronic conductivity to promote capacity utilization. However, LNO suffers from poor air stability and is prone to side reactions with the electrolyte. To address these issues, this invention uses lithium oxalate and / or lithium squartz as an outer shell layer to inhibit contact between LNO and air, moisture, etc., providing a barrier effect and reducing residual alkali on the LNO surface. Furthermore, the redox activity of Ni in the LNO described in this invention can significantly reduce the activation energy and decomposition voltage of lithium oxalate and / or lithium squartz, further promoting Li-… + By removing impurities and increasing the capacity of the composite lithium replenishing agent, the core, intermediate layer and outer shell of this invention work together to construct a composite lithium replenishing agent with high lithium replenishing capacity, low gas production, low residual alkali and high air stability.

[0008] Preferably, the molar ratio of the core to the intermediate layer is (1~2):(8~9), for example, it can be 1:9, 1.25:8.75, 1.5:8.5 or 2:8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0009] The molar ratio of the core and intermediate layer described in this invention is within a specific range. If the intermediate layer is too small relative to the core, the lithium replenishment capacity of the material body will be low. In addition, the poor conductivity of the core will significantly reduce the overall lithium replenishment capacity, resulting in poor practicality. If the intermediate layer is too large relative to the core, the air stability of the material is difficult to control within the design range, and there is a risk of relatively increased gas production, which may cause cell safety issues.

[0010] Preferably, the outer shell layer is 1wt% to 3wt% of the composite lithium supplement, for example, it can be 1wt%, 1.5wt%, 2wt%, 2.5wt% or 3wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0011] If the proportion of the outer shell layer described in this invention is too small, the residual alkali on the surface of the composite lithium replenishing agent will be high, and the air stability protection effect will be poor. If the proportion of the outer shell layer is too large, the conductivity of the composite lithium replenishing agent will be poor, resulting in low capacity. Furthermore, during delithiation, CO and CO2 will be released, and excessive gas production will cause cell safety risks.

[0012] Preferably, the particle size D50 of the kernel is 6μm to 10μm, for example, it can be 6μm, 7μm, 8μm, 9μm or 10μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0013] Preferably, the lithium-rich lithium titanium manganese oxide has the general chemical formula Li. a Ti x Mn y O2, where 0.3≤x≤0.4, for example, can be 0.3, 0.32, 0.34, 0.36, 0.38 or 0.4; 0.4≤y≤0.5, for example, can be 0.4, 0.42, 0.44, 0.46, 0.48 or 0.5; 0.7≤x+y≤0.8, for example, can be 0.7, 0.72, 0.74, 0.76, 0.78 or 0.8; 1.2≤a≤1.3, for example, can be 1.20, 1.25 or 1.30, but not limited to the listed values, other unlisted values ​​within the range also apply.

[0014] Preferably, the lithium-rich nickel oxide has the general chemical formula Li. b NiO3, where 2.0≤b≤2.1, for example, can be 2.0, 2.02, 2.04, 2.06, 2.08 or 2.1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] Secondly, the present invention provides a method for preparing the composite lithium supplement as described in the first aspect, the method comprising the following steps:

[0016] (1) The manganese source solution, titanium source solution, first precipitant solution and first complexing agent solution are subjected to a first precipitation reaction to obtain a titanium-manganese precursor;

[0017] The lithium source and the titanium-manganese precursor are mixed and sintered for the first time to obtain the core;

[0018] (2) The core, nickel source solution, second precipitant solution and second complexing agent solution described in step (1) are subjected to a second precipitation reaction to obtain a core coated with nickel precursor;

[0019] The lithium source and the nickel precursor-coated core are mixed and then sintered to obtain a core with an intermediate layer.

[0020] (3) The core and outer shell solution of the coating intermediate layer described in step (2) are mixed, heated and dried to obtain the composite lithium supplement.

[0021] Preferably, the temperature of the first precipitation reaction in step (1) is 55℃~70℃, for example, it can be 55℃, 60℃, 65℃ or 70℃, and the pH is 9-11, for example, it can be 9, 9.5, 10, 10.5 or 11, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] And / or, in step (1), the concentration of the complexing agent in the first precipitation reaction system is 3 g / L to 5 g / L, for example, it can be 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L or 5 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the manganese source in the manganese source solution in step (1) includes any one or a combination of at least two of manganese sulfate monohydrate, manganese sulfate tetrahydrate, manganese chloride tetrahydrate, or manganese nitrate.

[0024] Preferably, the titanium source in the titanium source solution in step (1) includes any one or a combination of at least two of titanium oxysulfate, titanium sulfate, titanium oxysulfate ammonium, or titanium tetrachloride solution.

[0025] Preferably, the first precipitant solution in step (1) and the second precipitant solution in step (2) each independently comprise any one or a combination of at least two of sodium hydroxide, potassium hydroxide, or lithium hydroxide.

[0026] Preferably, the concentrations of the first precipitant solution in step (1) and the second precipitant solution in step (2) are independently 0.1 mol / L to 1 mol / L, for example, 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 0.7 mol / L, 0.9 mol / L or 1 mol / L, but are not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the concentrations of the first complexing agent solution in step (1) and the second complexing agent solution in step (2) are independently 2 mol / L to 4 mol / L, for example, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L, but are not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the temperature of the first sintering in step (1) is 800℃~900℃, for example, 800℃, 825℃, 850℃ or 900℃, and the time is 12h~20h, for example, 12h, 14h, 16h, 18h or 20h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the atmosphere for the first sintering in step (1) includes air or oxygen.

[0030] Preferably, the molar ratio of lithium element in the lithium source and total metal element in the titanium-manganese precursor in step (1) is (1.2~1.3):(0.7~0.8), for example, it can be 1.2:0.8, 1.25:0.75 or 1.3:0.7, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the temperature of the second precipitation reaction in step (2) is 55℃~70℃, for example, 55℃, 60℃, 65℃ or 70℃, and the pH is 9-11, for example, 9, 9.5, 10, 10.5 or 11, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the concentration of the complexing agent in the second precipitation reaction system in step (2) is 3 g / L to 5 g / L, for example, it can be 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L or 5 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the nickel source in the nickel source solution in step (2) includes any one or a combination of at least two of nickel oxalate, nickel sulfate, nickel chloride, nickel nitrate, or nickel dicerocene.

[0034] Preferably, the second sintering temperature in step (2) is 650℃~740℃, for example, it can be 650℃, 670℃, 690℃, 710℃, 730℃ or 740℃, and the time is 10h~20h, for example, it can be 10h, 12.5h, 15h, 17.5h or 20h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the atmosphere for the second sintering in step (2) includes an inert gas.

[0036] Preferably, the molar ratio of lithium in the lithium source and nickel in the nickel precursor-coated core in step (2) is (2.0~2.1):1, for example, it can be 2.0:1, 2.02:1, 2.05:1, 2.07:1 or 2.1:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the concentration of the outer shell solution in step (3) is 0.5wt% to 1wt%, for example, it can be 0.5wt%, 0.7wt%, 0.9wt% or 1wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the heating reaction temperature in step (3) is 100℃~300℃, for example, it can be 100℃, 150℃, 200℃, 250℃ or 300℃, and the time is 3h~5h, for example, it can be 3h, 3.5h, 4h, 4.5h or 5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Thirdly, the present invention provides a lithium-ion battery comprising the composite lithium replenishing agent as described in the first aspect.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] This invention uses lithium-rich lithium manganese titanate as the core, Ti 4+ While lithium-rich lithium titanium manganese oxide (LNO) can suppress oxygen evolution and phase transition, and exhibits low high-pressure gas production, its theoretical capacity is relatively low, and its electronic conductivity is poor, resulting in low lithium replenishment capacity. To address these issues, lithium-rich lithium nickel oxide (LNO) is used as an intermediate layer. LNO possesses strong Ni-O covalent bonds, which can suppress Mn migration in LNO, further enhancing structural stability, reducing gas production, and improving the material's electronic conductivity to promote capacity utilization. However, LNO suffers from poor air stability and is prone to side reactions with the electrolyte. To address these issues, this invention uses lithium oxalate and / or lithium squartz as an outer shell layer to inhibit contact between LNO and air, moisture, etc., providing a barrier effect and reducing residual alkali on the LNO surface. Furthermore, the redox activity of Ni in the LNO described in this invention can significantly reduce the activation energy and decomposition voltage of lithium oxalate and / or lithium squartz, further promoting Li-… + By removing impurities and increasing the capacity of the composite lithium replenishing agent, the core, intermediate layer and outer shell of this invention work together to construct a composite lithium replenishing agent with high lithium replenishing capacity, low gas production, low residual alkali and high air stability. Detailed Implementation

[0042] 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.

[0043] Example 1

[0044] This embodiment provides a composite lithium replenishing agent, which includes a core, an intermediate layer, and an outer shell layer, wherein the intermediate layer covers the surface of the core, and the outer shell layer covers the surface of the intermediate layer away from the core.

[0045] The core is lithium-rich lithium titanate (chemical formula Li). 1.2 Ti 0.4 Mn 0.4O2, the intermediate layer is lithium nickel oxide rich in lithium (chemical formula Li). 2.05 NiO3), the outer shell layer is lithium squaric acid;

[0046] The core has a particle size D50 of 8 micrometers, the molar ratio of the core to the intermediate layer is 1.5:8.5, and the outer shell is 2 wt% of the composite lithium supplement.

[0047] The preparation method of the composite lithium supplement described in this embodiment includes the following steps:

[0048] (1) A first precipitation reaction was carried out in a tetrahydrate manganese sulfate solution, a titanium oxysulfate solution, a 0.5 mol / L potassium hydroxide solution and a 2 mol / L ammonia solution at a temperature of 60°C, a pH of 10 and an ammonia concentration of 4 g / L to obtain a titanium manganese precursor, wherein the tetrahydrate manganese sulfate solution and the titanium oxysulfate solution were prepared according to the elemental ratio of lithium-rich lithium manganese titanate.

[0049] Lithium carbonate and the titanium-manganese precursor were mixed in a molar ratio of lithium to titanium + manganese of 1.2:0.8 (molar ratio of titanium to manganese of 0.4:0.4), and then sintered in air at 880°C for 15 hours to obtain the core.

[0050] (2) The core described in step (1), nickel nitrate solution, 0.5 mol / L potassium hydroxide solution and 3 mol / L ammonia solution are subjected to a second precipitation reaction at a temperature of 60°C, a pH of 10 and an ammonia concentration of 5 g / L to obtain a nickel precursor-coated core.

[0051] The lithium nitrate and the nickel precursor-coated core were mixed in a lithium to nickel molar ratio of 2.05:1, and then subjected to a second sintering at 710°C for 12 hours under a nitrogen atmosphere to obtain a core with an intermediate layer.

[0052] (3) The core of the intermediate layer described in step (2) is mixed with a lithium squaric acid solution with a concentration of 0.5 wt% (mixed according to the formula amount), and then heated at 200°C for 5 h. Finally, it is dried to obtain the composite lithium supplement.

[0053] Example 2

[0054] This embodiment provides a composite lithium replenishing agent, which includes a core, an intermediate layer, and an outer shell layer, wherein the intermediate layer covers the surface of the core, and the outer shell layer covers the surface of the intermediate layer away from the core.

[0055] The core is lithium-rich lithium titanate (chemical formula Li). 1.25 Ti 0.3 Mn0.45 O2), the intermediate layer is lithium-rich nickel oxide (chemical formula Li). 2.0 NiO3), the outer shell layer is lithium squaric acid;

[0056] The core has a particle size D50 of 6 micrometers, the molar ratio of the core to the intermediate layer is 2:8, and the outer shell is 1 wt% of the composite lithium supplement.

[0057] The preparation method of the composite lithium supplement described in this embodiment includes the following steps:

[0058] (1) A first precipitation reaction was carried out in a manganese sulfate tetrahydrate solution, a titanium sulfate solution, a 1 mol / L potassium hydroxide solution and a 2 mol / L ammonia solution at a temperature of 70°C, a pH of 11 and an ammonia concentration of 3 g / L to obtain a titanium manganese precursor, wherein the manganese sulfate tetrahydrate solution and the titanium oxysulfate solution were prepared according to the elemental ratio of lithium-rich lithium manganese titanate.

[0059] Lithium carbonate and the titanium-manganese precursor were mixed in a molar ratio of lithium to titanium + manganese of 1.25:0.75 (molar ratio of titanium to manganese of 0.3:0.45), and then sintered in air at 850°C for 16 hours to obtain the core.

[0060] (2) The core, nickel nitrate solution, 0.1 mol / L sodium hydroxide solution and 2 mol / L ammonia solution described in step (1) are subjected to a second precipitation reaction at a temperature of 50°C, a pH of 9 and an ammonia concentration of 5 g / L to obtain a core coated with nickel precursor.

[0061] The lithium nitrate and the nickel precursor-coated core were mixed in a lithium to nickel molar ratio of 2.0:1, and then subjected to a second sintering at 650°C for 20 hours under a nitrogen atmosphere to obtain a core coated with an intermediate layer.

[0062] (3) The core of the intermediate layer described in step (2) is mixed with a lithium squaric acid solution with a concentration of 0.8 wt% (mixed according to the formula amount), and then heated at 100°C for 5 h. Finally, it is dried to obtain the composite lithium supplement.

[0063] Example 3

[0064] This embodiment provides a composite lithium replenishing agent, which includes a core, an intermediate layer, and an outer shell layer, wherein the intermediate layer covers the surface of the core, and the outer shell layer covers the surface of the intermediate layer away from the core.

[0065] The core is lithium-rich lithium titanate (chemical formula Li). 1.3 Ti 0.3 Mn0.4 O2), the intermediate layer is lithium-rich nickel oxide (chemical formula Li). 2.1 NiO3), the outer shell layer is lithium squaric acid;

[0066] The core has a particle size D50 of 10 micrometers, the molar ratio of the core to the intermediate layer is 1:9, and the outer shell is 3 wt% of the composite lithium supplement.

[0067] The preparation method of the composite lithium supplement described in this embodiment includes the following steps:

[0068] (1) Manganese sulfate tetrahydrate solution, titanium tetrachloride solution, 0.1 mol / L sodium hydroxide solution and 4 mol / L ammonia solution are subjected to a first precipitation reaction at a temperature of 62°C, a pH of 9 and an ammonia concentration of 5 g / L to obtain a titanium manganese precursor, wherein the manganese sulfate tetrahydrate solution and titanium oxysulfate solution are prepared according to the elemental ratio of lithium-rich lithium manganese titanate.

[0069] Lithium carbonate and the titanium-manganese precursor were mixed in a molar ratio of lithium to titanium + manganese of 1.3:0.7 (molar ratio of titanium to manganese of 0.3:0.4), and then sintered in air at 830°C for 18 hours to obtain the core.

[0070] (2) The core, nickel nitrate solution, 1 mol / L potassium hydroxide solution and 4 mol / L ammonia solution described in step (1) are subjected to a second precipitation reaction at a temperature of 60°C, a pH of 11 and an ammonia concentration of 3 g / L to obtain a nickel precursor-coated core.

[0071] The lithium nitrate and the nickel precursor-coated core were mixed in a lithium to nickel molar ratio of 2.1:1, and then sintered at 740°C for 10 hours under a nitrogen atmosphere to obtain a core with an intermediate layer.

[0072] (3) The core of the intermediate layer described in step (2) is mixed with a lithium squaric acid solution with a concentration of 1 wt% (mixed according to the formula amount), and then heated at 300°C for 3 hours. Finally, it is dried to obtain the composite lithium supplement.

[0073] Example 4

[0074] This embodiment provides a composite lithium supplement, which is the same as in Embodiment 1 except that the outer shell layer is lithium oxalate.

[0075] The preparation method of the composite lithium supplement in this embodiment is the same as that in Example 1, except that the lithium squaric acid solution of equal concentration in step (3) is replaced with lithium oxalate solution.

[0076] Example 5

[0077] This embodiment provides a composite lithium replenishing agent, which is the same as that in Example 1 except that the molar ratio of the core and the intermediate layer is 0.5:9.5.

[0078] The preparation method of the composite lithium supplement described in this embodiment is the same as that in Example 1, except that the molar ratio of the core and the intermediate layer is adapted to the change.

[0079] Example 6

[0080] This embodiment provides a composite lithium replenishing agent, which is the same as that in Embodiment 1 except that the molar ratio of the core and the intermediate layer is 2.5:7.5.

[0081] The preparation method of the composite lithium supplement described in this embodiment is the same as that in Example 1, except that the molar ratio of the core and the intermediate layer is adapted to the change.

[0082] Example 7

[0083] This embodiment provides a composite lithium replenishing agent, which is the same as in Example 1 except that the outer shell layer is 5 wt% of the composite lithium replenishing agent.

[0084] The preparation method of the composite lithium supplement described in this embodiment is the same as that in Example 1, except that the formulation amount is adapted according to the proportion of the outer shell layer.

[0085] Example 8

[0086] This embodiment provides a composite lithium replenishing agent, which is the same as in Example 1 except that the outer shell layer is 0.5 wt% of the composite lithium replenishing agent.

[0087] The preparation method of the composite lithium supplement described in this embodiment is the same as that in Example 1, except that the formulation amount is adapted according to the proportion of the outer shell layer.

[0088] Comparative Example 1

[0089] This comparative example provides a composite lithium replenishing agent, which is the same as that in Example 1 except that it does not include an intermediate layer.

[0090] The preparation method of the composite lithium supplement described in this comparative example is the same as that in Example 1, except that step (2) is not performed.

[0091] Comparative Example 2

[0092] This comparative example provides a composite lithium replenishing agent, which is the same as that in Example 1 except that it does not include the outer shell layer.

[0093] The preparation method of the composite lithium supplement described in this comparative example is the same as that in Example 1, except that step (3) is not performed.

[0094] Comparative Example 3

[0095] This comparative example provides a composite lithium replenishing agent, which is the same as that in Example 1 except that the outer shell layer is lithium dioxaborate.

[0096] The preparation method of the composite lithium supplement described in this comparative example is the same as that in Example 1, except that the lithium squaric acid solution of equal concentration in step (3) is replaced with lithium dioxalate borate solution.

[0097] The composite lithium replenishing agents obtained in the above examples and comparative examples were used to prepare lithium-ion batteries. The preparation process is as follows: (1) The lithium replenishing agent, SP (conductive carbon black) and PVDF (polyvinylidene fluoride) were mixed in a mass ratio of 85:10:5. After mixing, the mixture was homogenized to prepare a slurry with a solid content of 40%. Then, the slurry was prepared with 5 mg / cm³. 2 The electrode was coated with a surface density coating to prepare a 12mm diameter electrode sheet. After drying the electrode sheet, a coin cell was assembled. Charge-discharge tests were then performed: the electrode was charged to 4.4V at 25℃ and a 0.1C rate, followed by constant voltage charging until the current ≤0.01C. The charging capacity was the lithium replenishment capacity. After the electrode sheet was fully charged, the mass of the active material was recorded. Electrolyte was injected at an injection coefficient of 3.5g / Ah, and the electrode was sealed in an aluminum-plastic bag. After storage at 60℃ for 7 days, the gas production volume was recorded.

[0098] Air stability test: The composite lithium replenishing agents obtained in the above examples and comparative examples were placed in an air environment with 20% RH humidity and left for 72 hours before the above charging capacity test was performed.

[0099] Residual alkali content test: Weigh 3g of sample, add 100mL of pure water, stir and filter, then dilute the filtrate to 150mL. Take the filtrate and titrate with hydrochloric acid potentiometrically. Calculate the residual alkali content by Li2CO3 conversion through two jumps, and simultaneously perform blank correction to reduce errors.

[0100] The test results are shown in Table 1 below:

[0101] Table 1

[0102]

[0103] As can be seen from Table 1 above:

[0104] As can be seen from Examples 1-3 and Comparative Example 1, the intermediate layer described in this invention not only suppresses oxygen release and gas production in the core, but also has a reciprocal effect on the outer shell layer, promoting Li +The release of lithium enhances the lithium replenishment capacity, thereby improving the overall performance of the composite lithium replenishment agent. As shown in Examples 1-3 and Comparative Example 2, the outer shell layer of this invention protects the intermediate layer and improves the stability of the composite lithium replenishment agent. As shown in Examples 1-3 and Comparative Example 3, the outer shell layer of this invention uses lithium oxalate and / or lithium squartzate. Compared to other conventional organic lithium salts, lithium oxalate and / or lithium squartzate have higher lithium replenishment capacity, significantly improve air stability, reduce residual alkali, and produce harmless decomposition products with minimal residue. As shown in Examples 1 and 4, the outer shell layer of this invention can be lithium squartzate or lithium oxalate, preferably lithium squartzate, which has a lower decomposition potential, better air stability, and stronger conductivity. As shown in Examples 1 and 5-6, this invention preferably uses a molar ratio of the core and intermediate layer within a specific range to ensure the effective functioning of the core and intermediate layer. As shown in Examples 1 and 7-8, this invention preferably uses a mass ratio of the outer shell layer within a specific range to promote optimal function of the outer shell layer and improve the overall performance of the composite lithium replenishment agent.

[0105] 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 composite lithium supplement, characterized in that, The composite lithium replenishing agent includes a core, an intermediate layer, and an outer shell layer, wherein the intermediate layer covers the surface of the core, and the outer shell layer covers the surface of the intermediate layer away from the core. The core comprises lithium-rich lithium manganese titanate, the intermediate layer comprises lithium-rich lithium nickelate, and the outer shell layer comprises lithium oxalate and / or lithium squartzate.

2. The composite lithium supplement agent according to claim 1, characterized in that, The molar ratio of the core to the intermediate layer is (1~2):(8~9); And / or, the outer shell layer comprises 1wt% to 3wt% of the composite lithium supplement; And / or, the particle size D50 of the core is 6μm~10μm.

3. The composite lithium supplement agent according to claim 1 or 2, characterized in that, The general chemical formula of the lithium-rich lithium titanium manganese oxide is Li. a Ti x Mn y O2, where 0.3≤x≤0.4, 0.4≤y≤0.5, 0.7≤x+y≤0.8, and 1.2≤a≤1.3; And / or, the general chemical formula of the lithium-rich nickel oxide is Li b NiO3, where 2.0≤b≤2.

1.

4. A method for preparing the composite lithium supplement as described in any one of claims 1-3, characterized in that, The preparation method of the composite lithium supplement includes the following steps: (1) The manganese source solution, titanium source solution, first precipitant solution and first complexing agent solution are subjected to a first precipitation reaction to obtain a titanium-manganese precursor; The lithium source and the titanium-manganese precursor are mixed and sintered for the first time to obtain the core; (2) The core, nickel source solution, second precipitant solution and second complexing agent solution described in step (1) are subjected to a second precipitation reaction to obtain a core coated with nickel precursor; The lithium source and the nickel precursor-coated core are mixed and then sintered to obtain a core with an intermediate layer. (3) The core and outer shell solution of the coating intermediate layer described in step (2) are mixed, heated and dried to obtain the composite lithium supplement.

5. The preparation method of the composite lithium supplement according to claim 4, characterized in that, In step (1), the temperature of the first precipitation reaction is 55℃~70℃, and the pH is 9-11; And / or, in step (1), the concentration of the complexing agent in the first precipitation reaction system is 3 g / L to 5 g / L.

6. The method for preparing the composite lithium supplement according to claim 4 or 5, characterized in that, The concentrations of the first precipitant solution in step (1) and the second precipitant solution in step (2) are independently 0.1 mol / L to 1 mol / L; And / or, the concentrations of the first complexing agent solution in step (1) and the second complexing agent solution in step (2) are independently 2 mol / L to 4 mol / L; And / or, in step (1), the temperature of the first sintering is 800℃~900℃ and the time is 12h~20h.

7. The method for preparing the composite lithium supplement according to claim 4 or 5, characterized in that, In step (2), the temperature of the second precipitation reaction is 50℃~60℃, and the pH is 9-11; And / or, in step (2), the concentration of the complexing agent in the second precipitation reaction system is 3 g / L to 5 g / L.

8. The method for preparing the composite lithium supplement according to claim 4 or 5, characterized in that, Step (2) The second sintering temperature is 650℃~740℃ and the time is 10h~20h.

9. The method for preparing the composite lithium supplement according to claim 4 or 5, characterized in that, The concentration of the outer shell solution in step (3) is 0.5wt%~1wt%; And / or, the heating reaction in step (3) is carried out at a temperature of 100℃~300℃ for 3h~5h.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the composite lithium replenishing agent as described in any one of claims 1-3.

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