Preparation method of positive pole lithium supplement additive, additive, positive pole piece and battery

Abstract

The invention relates to the field of lithium ion battery materials, and particularly provides a preparation method of a positive electrode lithium supplement additive, the additive, a positive electrode plate and a battery, the preparation method of the positive electrode lithium supplement additive comprises the step of sintering a mixture of a lithium-rich lithium ferrite sintered body, an aluminum source and a cobalt source under an oxygen-free condition. According to the method disclosed by the invention, a multi-pass sintering and Al / Co co-coating process is adopted, so that residual lithium on the surface of the lithium-rich lithium ferrite material is greatly reduced, the surface coating integrity of the material is improved, the surface defects of the material are reduced, and the safety performance of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion battery materials, and specifically provides a preparation method of a cathode lithium supplement additive, an additive, a cathode electrode sheet and a battery. Background Art

[0002] At present, the newly installed capacity of new energy represented by solar energy in the global power generation is increasing continuously. However, new energy power generation has the characteristics of periodicity. In order to effectively improve the stability of new energy power generation, it is necessary to synchronously support energy storage devices. Lithium-ion batteries have the characteristics of high safety and high energy density, and are the mainstream choice for current energy storage devices. At present, the market demand for the life of lithium-ion batteries for energy storage is increasing day by day. Lithium supplement agents can effectively improve the cycle life of lithium-ion batteries and are indispensable additives in long-life lithium-ion batteries.

[0003] At present, lithium-ion battery lithium supplement agents are mainly divided into two categories: cathode lithium supplement and anode lithium supplement. Among them, anode lithium supplement has a high risk coefficient and great processing difficulty, making it difficult to achieve commercialization. Cathode lithium supplement has high feasibility and is perfectly compatible with existing production lines. At present, there are two commercially available cathode lithium supplement agents, lithium-rich nickelate and lithium-rich ironate. Lithium-rich nickelate Li2NiO2 has a low charging specific capacity, a relatively high reversible capacity, a weak lithium supplement effect, and contains precious metal nickel elements, resulting in a high cost. Lithium-rich ironate Li5FeO4 (subsequently abbreviated as LFO) has a high charging specific capacity, reaching more than 700 mAh / g, a low reversible capacity, an excellent lithium supplement effect, and wide raw material sources and low costs.

[0004] At present, the main preparation method of LFO is the high-temperature solid-phase method. However, the existing high-temperature solid-phase method for preparing LFO materials will leave more residual lithium on the material surface, such as lithium carbonate, lithium hydroxide, lithium oxide, etc. In the actual battery cell system, these residual lithium will affect the performance of the battery cell. First, the residual lithium will react with the cathode binder PVDF, making the binder deactivate and the adhesion effect of the active material particles worse. Long-term use will cause the active material to fall off from the electrode sheet. Second, the residual lithium will react with the electrolyte to generate gas, causing the battery cell to bulge and posing a safety hazard. Summary of the Invention

[0005] In order to overcome the above defects, the present invention provides a preparation method of a cathode lithium supplement additive, an additive, a cathode electrode sheet and a battery, which can greatly reduce the residual lithium on the surface of the lithium-rich ironate material, reduce the surface defects of the material, and improve the safety performance of the battery.

[0006] In the first aspect, the present invention provides a preparation method of a cathode lithium supplement additive, including:

[0007] Sintering a mixture of a lithium-rich ironate sintered body, an aluminum source and a cobalt source under an oxygen-free condition.

[0008] Furthermore, the molar ratio of the aluminum element in the aluminum source to the cobalt element in the cobalt source is (0.5 - 2):1.

[0009] Furthermore, the mixture is obtained by mixing the lithium-rich lithium iron ferrite sintered body, the aluminum source, and the cobalt source; and / or

[0010] The sintering temperature is 600 - 700 °C, and the sintering time is 2 - 5 h.

[0011] Furthermore, the method for preparing the lithium-rich lithium iron ferrite sintered body includes:

[0012] Sintering a mixture of an iron source, a lithium source, and a carbon source under anaerobic conditions;

[0013] Crushing the sintered product.

[0014] Furthermore, the molar ratio of the iron element in the iron source, the lithium element in the lithium source, and the carbon element in the carbon source is 1:(5 - 6):(0.05 - 0.2).

[0015] Furthermore, it includes any one or more of the following features:

[0016] The lithium source includes one or more of LiOH·H2O, Li2CO3, Li2SO4, and LiCl;

[0017] The iron source includes one or more of Fe2O3, Fe2(SO4)3, and FeCl3;

[0018] The carbon source includes an organic carbon source.

[0019] Furthermore, the organic carbon source includes one or more of glucose and chitosan.

[0020] Furthermore, the mixture is obtained by mixing the iron source, the lithium source, and the carbon source;

[0021] And / or the sintering temperature for sintering the mixture of the iron source, the lithium source, and the carbon source under anaerobic conditions is 750 - 850 °C, and the sintering time is 10 - 15 h.

[0022] Furthermore, the crushing of the sintered product includes:

[0023] Crushing the sintered product to 300 - 325 mesh.

[0024] Furthermore, the aluminum source includes one or more of Al2O3, AlCl3, and Al2(SO4)3;

[0025] The cobalt source includes one or more of Co(OH)2, CoCl2, and CoSO4.

[0026] In a second aspect, the present invention provides a cathode lithium supplement additive, and the chemical formula of the cathode lithium supplement additive is Li5FeCo x Al y O4@C, where 0.0013 ≤ x ≤ 0.0027 and 0.0013 ≤ y ≤ 0.0027.

[0027] In a third aspect, the present invention provides a cathode electrode sheet, including:

[0028] a current collector;

[0029] cathode active material; and

[0030] the cathode lithium supplement additive according to the second aspect or the cathode lithium supplement additive prepared by the method according to the first aspect.

[0031] In a fourth aspect, the present invention provides a lithium-ion battery, including the cathode electrode sheet according to the third aspect.

[0032] One or more of the above technical solutions of the present invention have at least one or more of the following

[0033] beneficial effects:

[0034] In implementing the technical solutions of the present invention, a two-step sintering process with Al and Co element co-coating is adopted, which greatly reduces the residual lithium on the surface of the lithium-rich lithium ferrite material, thereby improving the surface coating integrity of the material, reducing the surface defects of the material, and also enhancing the lithium supplement effect of the material, improving the cycling performance, reducing gas generation, and thus enhancing the battery safety performance. Description of the Drawings

[0035] Referring to the attached drawings, the disclosure of the present invention will become more understandable. It is easy for those skilled in the art to understand that these drawings are only for illustrative purposes and are not intended to limit the protection scope of the present invention. In addition, similar numbers in the figures are used to represent similar components, where:

[0036] Figure 1 is a schematic flow chart of the main steps of the preparation method of the cathode lithium supplement additive according to an embodiment of the present invention;

[0037] Figure 2 is a schematic diagram of the main reaction process according to Embodiment 1 of the present invention. Detailed Embodiments

[0038] Some embodiments of the present invention will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0039] The present invention provides a preparation method of a cathode lithium supplement additive. Referring to Figure 1 , including:

[0040] S1, sinter the mixture of lithium-rich lithium iron ferrite sintered body, aluminum source and cobalt source under an oxygen-free condition.

[0041] Through the secondary sintering of the sintered body and the Al / Co co-coating technology, the present invention can significantly improve the structural stability of the existing LFO material on the basis. This improvement method can effectively inhibit the occurrence of side reactions, thereby reducing the content of residual alkaline substances in the material and reducing the resistance value.

[0042] In one embodiment, the molar ratio of aluminum element in the aluminum source to cobalt element in the cobalt source is (0.5-2):1.

[0043] In one embodiment, the mixture in step S1 is obtained by mixing the lithium-rich lithium iron ferrite sintered body, aluminum source and cobalt source.

[0044] The specific process of sintering the mixture of the lithium-rich lithium iron ferrite sintered body with the aluminum source and cobalt source under an oxygen-free condition includes:

[0045] Mix the lithium-rich lithium iron ferrite sintered body with the aluminum source and cobalt source evenly to obtain a second mixture;

[0046] Sinter the second mixture formed by the lithium-rich lithium iron ferrite sintered body, aluminum source and cobalt source under an oxygen-free condition at a sintering temperature of 600-700 °C for 2-5 h. After sintering, Al / Co co-coated LFO is obtained.

[0047] After the aluminum source is sintered at a high temperature, a coating layer will be formed on the surface of LFO. This coating layer can effectively inhibit the side reaction between hydrofluoric acid in the electrolyte and the material, and improve the structural stability of the material.

[0048] During the sintering process, the cobalt source can react with residual lithium carbonate and lithium hydroxide on the material surface, greatly reducing the surface residual alkali, improving the gas generation during the actual use of the material, and enhancing the safety performance.

[0049] In one embodiment, the preparation method of the lithium-rich lithium iron ferrite sintered body includes:

[0050] S11, sinter the mixture of iron source, lithium source and carbon source under an oxygen-free condition;

[0051] The more specific process includes:

[0052] Mix the iron source, lithium source and carbon source evenly to obtain a first mixture.

[0053] First, fully mix the three raw materials of the iron source, lithium source and carbon source. To ensure the uniformity and efficiency of the mixing process, an efficient mixing device such as a high-speed mixer can be used to separately place the three raw materials of the iron source, lithium source and carbon source into the high-speed mixer. Start the device and let it be fully stirred and mixed under the action of high-speed rotation. In this way, under the strong action of the high-speed mixer, the raw materials can quickly reach a state of uniform mixing, thus laying a good foundation for the subsequent production process.

[0054] S12, sinter the first mixture under an oxygen-free condition. During the sintering process, an inert protective atmosphere plays a crucial role. It can effectively protect the reaction raw materials and prevent them from undergoing oxidation reactions under high-temperature conditions, thereby avoiding various possible side reactions. This protective measure ensures the smooth progress of the reaction and improves the purity and quality of the product.

[0055] After the sintering reaction, lithium-rich iron ferrite Li5FeO4 coated with carbon and having a core-shell structure is obtained.

[0056] S13, crush the sintered product.

[0057] To improve the effect of subsequent doping with aluminum and cobalt elements, lithium-rich iron ferrite Li5FeO4 is crushed.

[0058] Through multiple sintering processes and Al / Co co-coating technology, the structural stability of the existing LFO material can be significantly improved. This improvement method can effectively inhibit the occurrence of side reactions, thereby reducing the content of residual alkaline substances in the material and reducing the resistance value. In this way, the safety performance of the material is significantly improved. In addition, this improvement method has a high compatibility and matching degree with the existing material mass production line, and large-scale production can be achieved without additional new or modified existing equipment. This not only improves production efficiency but also reduces production costs, making this technology highly practical in industrial applications.

[0059] In one embodiment, the molar ratio of iron element in the iron source, lithium element in the lithium source and carbon element in the carbon source is 1:(5 - 6):(0.05 - 0.2).

[0060] The present invention first performs carbon coating treatment on the material. Specifically, instead of performing carbon doping or carbon coating after preparing LFO, the iron source, lithium source, and carbon source are mixed, and then the carbon coating is achieved through the sintering process. In this way, carbon coating can be synchronously carried out during the synthesis of lithium-rich lithium ferrate, significantly enhancing its conductivity and stability. As a result, the discharge performance and cycle life of the battery are significantly improved.

[0061] In addition, through the carbon coating in a specific proportion in the steps of the present invention, during the charge and discharge process of the battery, the particle breakage caused by the change in the lattice volume of the material can be slowed down, and at the same time, the increase in the material structure loss caused by the dissolution of transition metal ions in the active material to the negative electrode can be inhibited, thereby further improving the overall stability of the battery. This improvement not only enhances the performance of the battery but also improves the consistency between different battery cells, which is beneficial to the stability of the module and enhances its reliability and safety in practical applications.

[0062] In one embodiment, the lithium source includes one or more of LiOH·H2O, Li2CO3, Li2SO4, and LiCl.

[0063] In one embodiment, the iron source includes one or more of Fe2O3, Fe2(SO4)3, and FeCl3.

[0064] In one embodiment, the carbon source includes an organic carbon source.

[0065] In one embodiment, the organic carbon source includes one or more of glucose and chitosan.

[0066] In one embodiment, during the process of sintering the mixture of the iron source, lithium source, and carbon source under an oxygen-free condition, the sintering temperature is 750 - 850 °C, and the sintering time is 10 - 15 h. That is, in step S12, the sintering of the first mixture under an oxygen-free condition includes:

[0067] Sintering the first mixture under an oxygen-free condition at 750 - 850 °C for 10 - 15 h.

[0068] The present invention performs synthesis by adopting a specific two-step sintering process. This process can ensure that the particles can develop healthily during the sintering process and avoid the decline of material performance caused by agglomeration. Specifically, the sintering process needs to be carried out under specific temperature conditions. The selection of this temperature range is crucial because it directly affects the growth and distribution of the particles. If the sintering temperature is too high, the particles may grow excessively, resulting in agglomeration and thus reducing the material performance; on the contrary, if the sintering temperature is too low, the development of the particles may be insufficient or incomplete, which will also affect the final performance of the material. Therefore, by precisely controlling the sintering temperature, the synthesized material has excellent performance.

[0069] In one embodiment, the aluminum source includes one or more of Al2O3, AlCl3, and Al2(SO4)3;

[0070] The cobalt source includes one or more of Co(OH)2, CoCl2, and CoSO4.

[0071] In one embodiment, in step S13, the pulverizing of the sintered product includes:

[0072] Pulverize the product after sintering treatment to ensure that its particle size reaches between 300 and 325 mesh.

[0073] The pulverizing process can be carried out in a pulverizing or grinding device such as a jet mill. During this pulverizing process, the particle size of the material is controlled to ensure the smooth progress of subsequent processing steps. After pulverizing, a co - coating treatment of Al element and Co element is carried out. Through this co - coating technology, the melting points of the Al source and the Co source can be effectively reduced, the Gibbs activation free energy on the surface of the active particles is reduced, and the molten Al and Co at high temperatures can be more fully and uniformly coated on the surface of the active particles. Through the co - coating technology, the modification effect of these elements on the LFO matrix can be significantly improved. This modification not only enhances the electrochemical performance of the material but also improves its structural stability, making it exhibit more excellent performance in various application scenarios.

[0074] The present invention adopts multi - pass sintering and Al / Co co - coating process, which greatly reduces the residual alkali on the surface of the lithium - rich lithium ferrate material, improves the integrity of the surface coating of the material, and reduces the surface defects of the material; it can enhance the lithium - supplementing effect of the material, improve the cycle performance, reduce gas generation, and enhance safety.

[0075] The oxygen - free condition involved in the present invention can be an Ar gas atmosphere or other inert gas - protected atmospheres.

[0076] The present invention also provides a cathode lithium - supplementing additive, and the chemical formula of the cathode lithium - supplementing additive is Li5FeCo x Al y O4@C, where 0.0013 ≤ x ≤ 0.0027 and 0.0013 ≤ y ≤ 0.0027.

[0077] The cathode lithium - supplementing additive is a lithium - rich lithium ferrate Li5FeO4 coated with carbon having a core - shell structure and doped with a certain amount of Co and Al elements.

[0078] The present invention also provides a cathode electrode sheet, including:

[0079] Current collector;

[0080] Cathode active material; and

[0081] The positive electrode lithium supplement additive described above or the positive electrode lithium supplement additive prepared by the above preparation method.

[0082] During use, the positive electrode active material and the positive electrode lithium supplement additive are mixed and then coated on the current collector.

[0083] A binder and a conductive agent can also be added during coating.

[0084] The present invention also provides a lithium-ion battery, including the positive electrode plate described above.

[0085] Next, different positive electrode lithium supplement additives are prepared through examples and comparative examples, and are respectively made into lithium-ion batteries to test their respective electrochemical performances.

[0086] Example 1: Li5FeCo 0.002 Al 0.002 O4@C

[0087] Referring to Figure 2 , 80 g of iron source Fe2O3, 231 g of lithium source LiOH·H2O, and 3.1 g of carbon source glucose are weighed and mixed evenly in a high-speed mixer, and then subjected to high-temperature primary sintering in a roller hearth kiln. The sintering temperature is 800 °C, the sintering duration is 12 h, the heating rate is 5 °C / min, and Ar atmosphere is passed during sintering. After sintering, the product is pulverized in an air flow crusher to 300 - 325 mesh, and the LFO matrix coated with C is obtained after pulverization. Subsequently, 0.204 g of Al2O3 and 0.186 g of Co(OH)2 are weighed, mixed with the aforementioned LFO matrix, and then subjected to secondary sintering in a roller hearth kiln. The sintering temperature is 650 °C, the sintering duration is 3 h, the heating rate is 5 °C / min, and Ar atmosphere is passed during sintering. After sintering, the product is mechanically ground and pulverized to obtain Al / Co co-coated LFO@C, which is the positive electrode lithium supplement additive of Example 1.

[0088] Example 2: Li5FeCo 0.0013 Al 0.0013 O4@C

[0089] Weigh 80 g of iron source Fe2O3, 210 g of lithium source LiOH·H2O, and 1.55 g of carbon source glucose, mix them evenly in a high-speed mixer, and then conduct a high-temperature primary sintering in a roller hearth kiln. The sintering temperature is 750 °C, the sintering duration is 10 h, the heating rate is 5 °C / min, and an Ar atmosphere is passed during sintering. After sintering, the product is crushed in an air jet mill to 300 - 325 mesh, and the LFO matrix coated with C is obtained after crushing. Then weigh 0.133 g of Al2O3 and 0.121 g of Co(OH)2, mix them evenly with the aforementioned LFO matrix, and then conduct a secondary sintering in a roller hearth kiln. The sintering temperature is 600 °C, the sintering duration is 2 h, the heating rate is 5 °C / min, and an Ar atmosphere is passed during sintering. After sintering, the product is mechanically ground and crushed to obtain Al / Co co-coated LFO@C, which is the cathode lithium supplement additive of Example 2.

[0090] Example 3: Li5FeCo 0.0027 Al 0.0027 O4@C

[0091] Weigh 80 g of iron source Fe2O3, 251 g of lithium source LiOH·H2O, and 6.2 g of carbon source glucose, mix them evenly in a high-speed mixer, and then conduct a high-temperature primary sintering in a roller hearth kiln. The sintering temperature is 850 °C, the sintering duration is 15 h, the heating rate is 5 °C / min, and an Ar atmosphere is passed during sintering. After sintering, the product is crushed in an air jet mill to 300 - 325 mesh, and the LFO matrix coated with C is obtained after crushing. Then weigh 0.275 g of Al2O3 and 0.251 g of Co(OH)2, mix them evenly with the aforementioned LFO matrix, and then conduct a secondary sintering in a roller hearth kiln. The sintering temperature is 700 °C, the sintering duration is 5 h, the heating rate is 5 °C / min, and an Ar atmosphere is passed during sintering. After sintering, the product is mechanically ground and crushed to obtain Al / Co co-coated LFO@C, which is the cathode lithium supplement additive of Example 3.

[0092] Comparative Example 1:

[0093] Weigh 80 g of Fe2O3, 231 g of LiOH·H2O, and 3.1 g of glucose, mix them evenly in a high-speed mixer, and then conduct a high-temperature primary sintering in a roller hearth kiln. The sintering temperature is 800 °C, the sintering duration is 12 h, the heating rate is 5 °C / min, and an Ar atmosphere is passed during sintering. After sintering, the product is crushed in an air jet mill, and the product obtained after crushing is the cathode lithium supplement additive of Comparative Example 1.

[0094] The difference between Comparative Example 1 and Example 1 is only that Comparative Example 1 did not conduct the co-coating of Al and Co elements, but only carbon coating.

[0095] Comparative Example 2:

[0096] Weigh 80 g of Fe2O3, 231 g of LiOH·H2O, and 3.1 g of glucose, mix them evenly in a high-speed mixer, then conduct a high-temperature primary sintering in a roller hearth kiln. The sintering temperature is 800 °C, the sintering duration is 12 h, the heating rate is 5 °C / min, and an Ar atmosphere is passed during sintering. After sintering, the product is crushed in an air jet mill, and the product is obtained after crushing. Then weigh 0.204 g of Al2O3, mix it evenly with the aforementioned LFO matrix, and then conduct a secondary sintering in a roller hearth kiln. The sintering temperature is 650 °C, the sintering duration is 3 h, the heating rate is 5 °C / min, and an Ar atmosphere is passed during sintering. After sintering, the product is mechanically ground and crushed to obtain Al-coated LFO, which is the cathode lithium supplement additive of Comparative Example 2.

[0097] The difference between Comparative Example 2 and Example 1 is only that Comparative Example 2 does not perform Co element coating, but only performs carbon and Al element coatings.

[0098] Comparative Example 3:

[0099] Weigh 80 g of Fe2O3, 231 g of LiOH·H2O, and 3.1 g of glucose, mix them evenly in a high-speed mixer, then conduct a high-temperature primary sintering in a roller hearth kiln. The sintering temperature is 800 °C, the sintering duration is 12 h, the heating rate is 5 °C / min, and an Ar atmosphere is passed during sintering. After sintering, the product is crushed in an air jet mill, and the LFO matrix is obtained after crushing. Then weigh 0.186 g of Co(OH)2, mix it evenly with the aforementioned LFO matrix, and then conduct a secondary sintering in a roller hearth kiln. The sintering temperature is 650 °C, the sintering duration is 3 h, the heating rate is 5 °C / min, and an Ar atmosphere is passed during sintering. After sintering, the product is mechanically ground and crushed to obtain Co-coated LFO, which is the cathode lithium supplement additive of Comparative Example 3.

[0100] The difference between Comparative Example 3 and Example 1 is only that Comparative Example 3 does not perform Al element coating, but only performs carbon and Co element coatings.

[0101] Comparative Example 4:

[0102] The difference between this comparative example and Example 1 is only that: during the high-temperature primary sintering, the sintering temperature is 870 °C, and the other steps are the same as those in Example 1, and finally the cathode lithium supplement additive of Comparative Example 4 is obtained.

[0103] Comparative Example 5:

[0104] The difference between this comparative example and Example 1 is only that: during the high-temperature primary sintering, the sintering temperature is 730 °C, and the other steps are the same as those in Example 1, and finally the cathode lithium supplement additive of Comparative Example 5 is obtained.

[0105] Comparative Example 6:

[0106] The difference between this comparative example and Example 1 is that during the secondary sintering, the sintering temperature is 720° C., and the remaining steps are the same as those in Example 1, and finally the positive electrode lithium supplement additive of Comparative Example 6 is obtained.

[0107] Comparative Example 7:

[0108] The difference between this comparative example and Example 1 is that during the secondary sintering, the sintering temperature is 580° C., and the remaining steps are the same as those in Example 1, and finally the positive electrode lithium supplement additive of Comparative Example 7 is obtained.

[0109] The positive electrode lithium supplement additive finally obtained in the above embodiments and comparative examples was evenly mixed with LFP material (lithium iron phosphate, purchased from Hunan Yuneng New Energy Battery Materials Co., Ltd.), PVDF and conductive carbon black in a ratio of 2:96:1:1, and NMP was added and stirred continuously until the slurry viscosity reached 8000 mPa·s.

[0110] Then, a doctor blade coater was used to evenly coat the slurry on both sides of the carbon-coated current collector aluminum foil. The coating density on one side was 18 mg / cm 2 Then, the foil with the slurry is dried in a vacuum oven to obtain the positive electrode sheet.

[0111] Graphite anode (purchased from Shanghai Shanshan Technology Co., Ltd.), conductive carbon black, styrene-butadiene rubber, polyacrylic acid, and carboxymethyl cellulose were mixed in a ratio of 96:1:1:1:1, and deionized water was added and stirred continuously until the slurry viscosity reached 6000mPa·s. Then, a blade coater was used to evenly coat the slurry on both sides of the carbon-coated copper foil, and the surface density of the coated single side was 9mg / cm 2 Then, the foil with the slurry is dried in a vacuum oven to obtain the negative electrode sheet.

[0112] The above-mentioned positive electrode sheet, negative electrode sheet, and separator (purchased from Yunnan Enjie New Materials Co., Ltd.) were wound into a soft-pack full battery (lithium-ion battery), and the electrolyte (purchased from Guangzhou Tianci High-tech Materials Co., Ltd.) was injected. The soft-pack full battery was then oxidized at high temperature and the first charging capacity was recorded. The soft-pack full battery was then subjected to a 0.5P cycle test at high temperature, and the cycle gas production was recorded. The cycle test system refers to GB / T36276-2023. The test results are shown in Table 1.

[0113] Table 1 Battery test data of Examples 1-3 and Comparative Examples 2-7

[0114] Initial charge capacity mAh / g Gas production volume mL after 1000 cycles Example 1 724 3 Example 2 722 3 Example 3 718 3 Comparative Example 1 626 35 Comparative Example 2 675 26 Comparative Example 3 679 29 Comparative Example 4 688 17 Comparative Example 5 670 19 Comparative Example 6 698 13 Comparative Example 7 702 12

[0115] From the test data in the above table, it can be seen that in Examples 1-3, two-stage sintering with an Al / Co co-coating process can significantly increase the initial charge capacity per gram and reduce the gas generation. This is because the cathode lithium supplement additive of the present invention can greatly reduce the residual alkali on the surface of the lithium-rich lithium ferrite material, improve the integrity of the surface coating of the material, reduce the surface defects of the material and enhance the lithium supplement effect of the material, improve the cycle performance, reduce the gas generation, and enhance the safety performance. Specifically, in the preparation of the cathode lithium supplement additive of the present invention, first, three raw materials of Fe2O3, LiOH, and glucose are sintered at high temperature to obtain an LFO matrix. Subsequently, the LFO matrix is mixed with Al2O3 and Co(OH)2 and then ground and sintered to obtain Al / Co co-coated LFO. After high-temperature sintering, Al2O3 will form an Al2O3 island-shaped coating layer on the surface of LFO, which can effectively inhibit the side reaction between hydrofluoric acid in the electrolyte and the material and improve the structural stability of the material. During the sintering process, Co(OH)2 can react with the residual lithium carbonate and lithium hydroxide on the material surface to generate LiCoO2, greatly reducing the surface residual alkali, improving the gas generation during the actual use of the material, and enhancing the safety performance. At the same time, this LiCoO2 layer, as a fast ion conductor, can reduce the resistivity of the material. When used in actual battery cells, it can reduce the DCR of the battery cell, reduce heat generation, and enhance the safety performance.

[0116] In Comparative Example 1, due to the absence of the two-stage sintering Al / Co co-coating process, its residual alkali is relatively high, the initial charge capacity per gram is low, and the cyclic gas generation is high.

[0117] In Comparative Examples 2 and 3, during the two-stage sintering, the types of coating elements are few, the surface coating effect is poor, the charge capacity per gram is also slightly low, and the cyclic gas generation is high.

[0118] In Comparative Example 4, due to the too high temperature during the one-stage sintering, the particles grew excessively and formed aggregates, so its performance is poor.

[0119] In Comparative Example 5, due to the too low temperature during the one-stage sintering, the particle growth is incomplete, and the performance is also poor. In Comparative Example 6, due to the too high temperature during the two-stage sintering, the particles agglomerated and the performance decreased.

[0120] In Comparative Example 7, the two-stage sintering temperature is too low to form a complete coating layer on the particle surface, and the performance is poor.

[0121] From the experimental data in Table 1, it can be seen that by modifying the lithium-rich lithium ferrite material using the preparation method of the present invention, the residual lithium left on the surface during the preparation of the LFO material can be reduced, thereby improving the cycle performance and safety performance during the actual use of the battery cell.

[0122] It should be noted that although the above embodiments describe the various steps in a specific order, those skilled in the art can understand that in order to achieve the effects of the present invention, it is not necessary for different steps to be executed in such an order. They can be executed simultaneously (in parallel) or in other orders, and these variations are all within the protection scope of the present invention.

[0123] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of the present invention.

Claims

1. A preparation method of a cathode lithium supplement additive, characterized in that, Comprising: Sintering a mixture of a lithium-rich lithium ferrite sintered body, an aluminum source, and a cobalt source under an oxygen-free condition.

2. The method according to claim 1, wherein The molar ratio of aluminum element in the aluminum source to cobalt element in the cobalt source is (0.5 - 2):

1.

3. The method according to claim 1, characterized in that, The mixture is obtained by mixing the lithium-rich lithium ferrite sintered body, the aluminum source, and the cobalt source; and / or The temperature of the sintering is 600 - 700 °C, and the time of the sintering is 2 - 5 h.

4. The method according to claim 1, wherein The preparation method of the lithium-rich lithium ferrite sintered body includes: Sintering a mixture of an iron source, a lithium source, and a carbon source under an oxygen-free condition; Crushing the sintered product.

5. The method according to claim 4, characterized in that, The molar ratio of iron element in the iron source, lithium element in the lithium source, and carbon element in the carbon source is 1:(5 - 6):(0.05 - 0.2).

6. The method according to claim 4, wherein Including any one or more of the following features: The lithium source includes one or more of LiOH·H2O, Li2CO3, Li2SO4, and LiCl; The iron source includes one or more of Fe2O3, Fe2(SO4)3, and FeCl3; The carbon source includes an organic carbon source; Preferably, the organic carbon source includes one or more of glucose and chitosan.

7. The method according to claim 4, characterized in that, The mixture is obtained by mixing the iron source, the lithium source, and the carbon source; and / or The sintering temperature for sintering the mixture of the iron source, the lithium source, and the carbon source under an oxygen-free condition is 750 - 850 °C, and the sintering time is 10 - 15 h.

8. The method according to claim 4, wherein The crushing of the sintered product includes: Crushing the sintered product to 300 - 325 mesh.

9. The method according to claim 1, wherein The aluminum source includes one or more of Al2O3, AlCl3, and Al2(SO4)3; The cobalt source includes one or more of Co(OH)2, CoCl2, and CoSO4.

10. A cathode lithium supplement additive, characterized in that, The chemical formula of the positive electrode lithium supplement additive is Li5FeCo x Al y O4@C, where 0.0013 ≤ x ≤ 0.0027 and 0.0013 ≤ y ≤ 0.0027.

11. A positive electrode sheet, characterized in that, Comprising: A current collector; A positive electrode active material; And The positive electrode lithium supplement additive according to claim 10 or the positive electrode lithium supplement additive prepared by the method according to any one of claims 1 - 10.

12. A lithium-ion battery, characterized in that, Including the positive electrode plate according to claim 11.

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