Lithium supplement, preparation method therefor, positive electrode sheet and secondary battery

Abstract

A lithium supplement, a preparation method therefor, a positive electrode sheet and a secondary battery. The lithium supplement comprises a first material phase and a second material phase, the first material phase comprising a lithium-rich material, and the second material phase comprising a reducing agent. The reducing agent can combine with active oxygen to inhibit a gas-producing reaction caused by the active oxygen, and the reducing agent can also combine with oxygen to reduce the gas output of a battery, thereby effectively improving the safety performance, the electrochemical performance and the stability of the battery. In addition, the reduction in the gas output of the battery reduces the battery impedance, helping to improve electron and ion conductivity and thus increasing the deintercalation rate of lithium ions during charging processes. Moreover, the reducing agent combining with the oxygen to generate a stable substance can avoid oxygen deintercalation again, thereby ensuring the reliability of the reducing agent for reducing the battery gas output.

Description

Lithium supplement and preparation method thereof, positive electrode sheet and secondary battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on July 21, 2023, with application number 202310911533.4, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of energy technology, and in particular to a lithium supplement and a preparation method thereof, a positive electrode sheet and a secondary battery. Background Art

[0003] During the first charge and discharge process of a battery, such as a lithium-ion secondary battery, a large amount of solid electrolyte interface film (SEI film) will be produced on the surface of the negative electrode of the battery, which consumes the limited lithium ions and electrolyte in the battery, causing irreversible capacity loss, resulting in a decrease in the coulombic efficiency of the lithium-ion secondary battery, and directly affecting the cycle life and energy density of the lithium-ion secondary battery. At present, this part of the irreversible capacity loss can be eliminated by adding lithium-supplementing materials to the positive electrode of the battery, thereby improving the battery energy density and other electrical properties. However, the existing lithium-supplementing materials have the problems of low capacity and high gas production. The high gas production of lithium-supplementing materials increases the battery impedance and reduces the battery safety and electrochemical performance, which is not conducive to the promotion and application of lithium-supplementing materials and limits the improvement of the performance of lithium-ion secondary batteries.

[0004] Summary of the Invention

[0005] The present application provides a lithium supplement agent and a preparation method thereof, a positive electrode plate and a secondary battery to solve the problem of high gas production of the lithium supplement agent.

[0006] In a first aspect, the present application provides a lithium supplement agent, which includes a first material phase and a second material phase, wherein the first material phase includes a lithium-rich material, and the second material phase includes a reducing agent.

[0007] In the embodiment of the present application, by adding a reducing agent to the lithium supplement, on the one hand, the reducing agent can combine with the active oxygen to inhibit the gas production reaction caused by the active oxygen, and the reducing agent can also combine with oxygen to reduce the gas production of the battery, effectively improving the safety performance, electrochemical performance and stability of the battery. In addition, reducing the gas production of the battery reduces the battery impedance, which is beneficial to improving the electronic and ion conductivity, thereby increasing the rate of lithium ion release during charging. On the other hand, the reducing agent combines with oxygen to produce a stable substance. The reducing agent and oxygen are combined at the chemical level, not a simple physical adsorption. The reducing agent combines with oxygen to form a stable substance to prevent oxygen from escaping again, ensuring the reliability of the reducing agent in reducing battery gas production.

[0008] In one embodiment, the first material phase is Li 5a+2b Fea M b O 4a+2b , where 0≤a≤1, 0≤b≤1, a and b are not 0 at the same time; M is a metal element.

[0009] In one embodiment, the metal element includes at least one metal element selected from the group consisting of divalent nickel, divalent manganese, divalent iron, and divalent cobalt.

[0010] In one embodiment, the reducing agent includes at least one of AlN, FeS, S, Fe2S3, Al2S3, Li2S, NiO, and MnO.

[0011] In one embodiment, the second material phase fills the gaps between the first material phases.

[0012] In one embodiment, the second material phase is doped in the first material phase.

[0013] In one embodiment, the second material is bonded to an outer surface of the first material phase.

[0014] In one embodiment, the mass ratio of the second material phase to the first material phase is 1%-20%.

[0015] In one embodiment, the lithium supplement further includes a coating layer, and the coating layer is coated on the outer surface of the first material phase and / or the second material phase.

[0016] In one embodiment, the coating layer includes at least one of an isolation coating layer, an ion conductor coating layer, and an electronic conductor coating layer.

[0017] In one embodiment, the surface residual alkali value of the lithium supplement agent is 0%-2%.

[0018] In one embodiment, the water absorption rate of the lithium supplement agent is less than 20 ppm / s at 25° C. and 30%-35% relative humidity in air.

[0019] In one embodiment, the water absorption rate of the lithium supplement agent is less than 10 ppm / s at 25° C. and 20%-25% relative humidity in air.

[0020] In one embodiment, the particle size D50 of the lithium supplement agent is 0.6 μm-40 μm.

[0021] In one embodiment, the specific surface area of ​​the lithium supplement is 0.1 m 2 / g-20m 2 / g.

[0022] In a second aspect, the present application provides a method for preparing a lithium supplement, the method comprising:

[0023] Adding lithium source, iron source and M source into the complexing agent solution and stirring to obtain gel;

[0024] sintering the gel in a protective atmosphere to obtain a first material phase;

[0025] The first material phase is mixed with a reducing agent, and sintered to obtain the lithium supplement agent.

[0026] In a third aspect, the present application provides a positive electrode plate, which includes the lithium supplement agent as described in any one of the above items, or the lithium supplement agent prepared by the preparation method of the lithium supplement agent as described above.

[0027] In a fourth aspect, the present application provides a secondary battery, comprising a negative electrode plate, a separator, and the positive electrode plate as described above.

[0028] In one embodiment, the secondary battery is a lithium-ion battery, and in the lithium-ion battery, the first delithiation capacity of the lithium supplement agent is greater than or equal to 500 mAh / g.

[0029] In one embodiment, the ratio of the first-cycle gas production of the lithium supplement agent to the first-cycle gas production of the corresponding Li5FeO4 is 1%-30%. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments of the present application will be described below.

[0031] FIG1 is a schematic structural diagram of a lithium supplement provided by one embodiment of the present application;

[0032] FIG2 is an EDS spectrum of the lithium supplement provided in Example 1 of the present application;

[0033] FIG3 is a SEM spectrum of the lithium supplement provided in Example 1 of the present application;

[0034] FIG4 is an EDS test element distribution diagram of element C in the lithium supplement provided in Example 1 of the present application;

[0035] FIG5 is an EDS test element distribution diagram of the O element of the lithium supplement provided in Example 1 of the present application;

[0036] FIG6 is an EDS test element distribution diagram of Al element of the lithium supplement provided in Example 1 of the present application;

[0037] FIG7 is an EDS test element distribution diagram of the S element of the lithium supplement provided in Example 1 of the present application;

[0038] FIG8 is an EDS test element distribution diagram of the Fe element in the lithium supplement provided in Example 1 of the present application. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments.

[0040] As used herein, the terms "first," "second," and the like are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, unless otherwise specified, "plurality" means two or more.

[0041] In addition, in this article, directional terms such as "upper" and "lower" are defined relative to the orientation of the structure schematically placed in the accompanying drawings. It should be understood that these directional terms are relative concepts. They are used for relative description and clarification, and they can change accordingly according to changes in the orientation of the structure.

[0042] For ease of understanding, the English abbreviations and related technical terms involved in the embodiments of this application are explained and described below.

[0043] Relative humidity: refers to the percentage of water vapor pressure in the air to the saturated water vapor pressure at the same temperature.

[0044] ppm: parts per million, which means one part per million. For gases, ppm refers to the mole fraction or volume fraction; for solutions, ppm refers to the mass concentration.

[0045] During the first charge and discharge process of a battery, such as a lithium-ion secondary battery, a large amount of solid electrolyte interface film (SEI film) will be produced on the surface of the negative electrode of the battery, which consumes the limited lithium ions and electrolyte in the battery, greatly reducing the capacity of lithium ions and causing irreversible capacity loss. During the first discharge, the lithium ions deintercalated from the negative electrode are much smaller than the lithium ions deintercalated from the positive electrode during charging, resulting in a decrease in the coulombic efficiency of the lithium-ion secondary battery, which directly affects the cycle life and energy density of the lithium-ion secondary battery. To address this problem, the loss of this part of irreversible capacity can usually be eliminated by replenishing lithium at the positive electrode, thereby improving the energy density and other electrical properties of the battery. However, existing lithium-replenishing materials have the problems of low capacity and high gas production. The high gas production of lithium-replenishing materials increases the battery impedance and reduces the battery safety and electrochemical performance, which is not conducive to the promotion and application of lithium-replenishing materials and limits the improvement of the performance of lithium-ion secondary batteries.

[0046] Please refer to FIG1 . The present application provides a lithium supplement agent 1 . The lithium supplement agent 1 includes a first material phase 11 and a second material phase 12 . The first material phase 11 includes a lithium-rich material, and the second material phase 12 includes a reducing agent.

[0047] The lithium supplement agent 1 is applied to the battery's positive electrode to pre-lithiate the positive electrode, adding lithium to the battery's interior to replenish lithium ions before operation. In one embodiment, the lithium supplement agent 1 can be applied to the outer surface of the battery's positive electrode tab, or embedded into the outer surface of the battery's positive electrode tab. In other embodiments, the lithium supplement agent 1 can be added during the preparation of the battery's positive electrode tab, dispersing the lithium supplement agent 1 onto the outer surface and interior of the battery's positive electrode tab.

[0048] The lithium supplement 1 includes a first material phase 11. The lithium-rich material in the first material phase 11 has a high lithium content. During the initial charge process, lithium (Li) in the lithium-rich material can be released and migrate to the battery's negative electrode, offsetting the irreversible lithium loss caused by the formation of the SEI film, thereby increasing the battery's total capacity and energy density. The lithium-rich material is a lithium-containing compound. The lithium-rich material can be a single lithium compound or a mixture of multiple lithium compounds.

[0049] The reducing agent can combine with oxygen to form a stable substance. For example, the reducing agent can react with oxygen. The reaction between the reducing agent and oxygen includes but is not limited to redox reaction.

[0050] The lithium supplement 1 may generate active oxygen during the charge and discharge process, and the active oxygen will generate oxygen. In the embodiment of the present application, by adding a reducing agent to the lithium supplement 1, on the one hand, the reducing agent can combine with the active oxygen to inhibit the gas production reaction caused by the active oxygen, and the reducing agent can also combine with oxygen to reduce the gas production of the battery, effectively improving the safety performance, electrochemical performance and stability of the battery. In addition, reducing the gas production of the battery reduces the battery impedance, which is beneficial to improving the electronic and ion conductivity, thereby increasing the rate of lithium ion release during the charging process. On the other hand, the reducing agent combines with oxygen to produce a stable substance. The reducing agent and oxygen are combined at the chemical level, not a simple physical adsorption. The reducing agent combines with oxygen to form a stable substance to prevent oxygen from escaping again, thereby ensuring the reliability of the reducing agent in reducing battery gas production.

[0051] In one embodiment, the first material phase 11 is Li 5a+2b Fe a M b O 4a+2b , where 0≤a≤1, 0≤b≤1, a and b are not 0 at the same time; M is a metal element. That is, the molecular formula of lithium-rich material is Li 5a+2b Fe a M b O 4a+2bLi represents lithium, Fe represents iron, and O represents oxygen.

[0052] In the embodiment of the present application, Li 5a+2b Fe a M b O 4a+2b As a lithium-rich material, the lithium replenisher 1 has a high lithium replenishment capacity, produces less gas during charging and discharging, and has high safety and electrochemical properties.

[0053] In the prior art, lithium ferrite, lithium nickelate, or lithium manganate is typically used as the lithium replenisher 1. When lithium ferrite (Li5FeO4) is used as the lithium replenisher 1, the capacity of lithium ferrite is high, but lithium ferrite produces a large amount of gas during charging, which increases battery impedance and reduces battery safety and electrochemical performance. In addition, lithium ferrite has a high residual alkalinity value, which easily causes gelation of the slurry during the slurry mixing process, resulting in poor slurry fluidity, which seriously affects the processing performance of the lithium replenisher 1. When lithium nickelate (such as Li2NiO2) or lithium manganate (such as Li2MnO2) is used as the lithium replenisher 1, although the gas production of lithium nickelate / lithium manganate during charging is small and the residual alkalinity value is low, the capacity of lithium nickelate / lithium manganate is low, and the lithium replenishment effect is poor, which limits the improvement of battery performance.

[0054] In this application, the chemical formula of the first material phase 11 in the lithium supplement 1 is Li 5a+2b Fe a M b O 4a+2b , Li 5a+2b Fe a M b O 4a+2b A relatively high capacity level can be maintained, and by providing a reducing agent to combine with oxygen to form a stable substance, the gas generation of the lithium supplement agent 1 is further reduced, and the stability of the lithium supplement agent 1 is improved.

[0055] Generally, a and b are not both 0. In one embodiment, a+b=1.

[0056] In one embodiment, M is a reducing metal element. M is selected from a metal with reducing properties. The reducing metal is easy to combine with oxygen and can inhibit the lithium supplement 1 from generating oxygen. In the first material phase 11, due to the addition of the reducing metal element, the Li 5a+2b Fe a M b O 4a+2b Activity of binding with water, Li 5a+2b Fe a M b O 4a+2bThe residual alkali value is low, and the gas production during charging is small, which improves the processing performance, safety performance and electrochemical performance of the lithium supplement 1. In this application, on the one hand, the chemical formula of the first material phase 11 is configured as Li 5a+2b Fe a M b O 4a+2b , reducing the gas production of the lithium supplement agent 1 from the source. On the other hand, by setting a reducing agent to combine with oxygen to form a stable substance, the gas production of the lithium supplement agent 1 is further reduced and the stability of the lithium supplement agent 1 is improved.

[0057] In one embodiment, the reducing metal element includes at least one metal element selected from divalent nickel, divalent manganese, divalent iron, and divalent cobalt. For example, when M is selected from Ni, the chemical formula of the first material phase 11 is Li 5a+2b Fe a Ni b O 4a+2b When M is selected from Mn, the chemical formula of the first material phase 11 is Li 5a+2b Fe a Mn b O 4a+2b When M is selected from Ni and Mn, the chemical formula of the first material phase 11 is Li 5a+2b Fe a Ni b1 Mn b2 O 4a+2b , where b1+b2=b.

[0058] Divalent nickel, divalent manganese, divalent iron and divalent cobalt can reduce the 5a+2b Fe a M b O 4a+2b The amount of gas produced during the charging process improves the safety and electrochemical performance of the lithium supplement 1.

[0059] In one embodiment, a>b. In the embodiment of the present application, controlling the Fe content to be greater than or equal to the M content can ensure the lithium replenishing effect of the lithium replenishing agent 1 while reducing the gas production of the lithium replenishing agent 1 to improve the stability of the lithium replenishing agent 1.

[0060] In one embodiment, the reducing agent includes at least one of AlN, FeS, S, Fe2S3, Al2S3, Li2S, NiO, and MnO. AlN, FeS, S, Fe2S3, Al2S3, Li2S, NiO, and MnO can react with oxygen to form a stabilizing substance to reduce battery gas production, thereby reducing battery impedance, effectively improving battery safety and electrochemical performance, and enhancing the stability of the lithium supplement 1.

[0061] For example, in one embodiment, the reducing agent includes NiO, which undergoes an oxidation-reduction reaction with oxygen to generate Ni2O3, which is relatively stable. The embodiment of the present application uses NiO as a reducing agent to effectively reduce the gas production of the battery.

[0062] In one embodiment, the reducing agent includes MnO, and MnO undergoes a redox reaction with oxygen to generate MnO2.

[0063] In one embodiment, the reducing agent includes Al2S3, and Al2S3 undergoes a redox reaction with oxygen to generate Al2O3 and S (elemental sulfur).

[0064] In one embodiment, the reducing agent includes AlN, and AlN undergoes a redox reaction with oxygen to generate aluminum oxide and nitrogen monoxide.

[0065] In one embodiment, when a is equal to or close to 0, or b is equal to or close to 0, the gas production of the lithium-rich material is large, and Al2S3 can be preferentially selected as the second material phase 12, which has the largest amount of combined oxygen, thereby effectively reducing the gas production of the lithium supplement agent 1.

[0066] In one embodiment, the second material phase 12 is filled in the gaps between the first material phase 11. The reducing agent is filled in the gaps between the particles of the lithium-rich material, which increases the compaction density of the lithium supplement agent 1, thereby increasing the capacity of the lithium supplement agent 1 and achieving a better lithium supplement effect.

[0067] In one embodiment, the second material phase 12 is doped with the first material phase 11. The second material phase 12 and the first material phase 11 are mixed, and the reducing agent is mixed with the lithium-rich material, which facilitates the preparation of the lithium supplement agent 1.

[0068] In one embodiment, the second material phase 12 is bonded to the outer surface of the first material phase 11. Since the lithium-rich material has a certain amount of residual alkali on its outer surface, the reducing agent is disposed on the outer surface of the lithium-rich material to reduce the overall residual alkali value of the lithium supplement 1, thereby improving the processing performance and safety performance of the lithium supplement 1.

[0069] In one embodiment, the lithium supplement agent 1 is further doped with a metal element, wherein the metal element includes at least one of aluminum, titanium, zirconium, vanadium, manganese, and cerium. Doping the lithium supplement agent 1 with a metal element such as aluminum, titanium, zirconium, vanadium, manganese, and cerium can improve the structural stability of the lithium supplement agent 1.

[0070] In one embodiment, the mass ratio of the second material phase 12 to the first material phase 11 is 1%-20%. The relative content of the second material phase 12 to the first material phase 11 affects the performance of the lithium supplement 1. If the content of the second material phase 12 is too low, the second material phase 12 will have little effect on reducing the gas production of the lithium supplement 1. If the content of the second material phase 12 is too high, the proportion of the lithium-rich material will be reduced, thereby reducing the amount of lithium supplemented by the lithium supplement 1 and affecting the lithium supplement effect of the lithium supplement 1.

[0071] In the embodiment of the present application, the mass ratio of the second material phase 12 to the first material phase 11 in the lithium supplement agent 1 is set within the range of 1%-20%. While ensuring that the lithium supplement agent 1 has a good lithium supplement effect, it can also better reduce the gas production of the lithium supplement agent 1 during the charging and discharging process, thereby reducing the battery impedance and effectively improving the battery's safety performance, electrochemical performance and stability.

[0072] In one embodiment, the mass ratio of the second material phase 12 to the first material phase 11 can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%.

[0073] In one embodiment, the lithium supplement agent 1 further includes a coating layer 20, which is coated on the outer surface of the first material phase 11 and / or the second material phase 12. The lithium supplement agent 1 has a core-shell structure. The core 10 of the lithium supplement agent 1 includes the first material phase 11 and the second material phase 12. The outer shell of the lithium supplement agent 1, i.e., the coating layer 20, is coated on the outer surface of the core 10. The coating layer 20 can fully or partially coat the outer surface of the core 10. The coating layer 20 can protect the core 10. It is understood that if the coating layer 20 is not provided and only the core 10 is used as the lithium supplement agent 1, on the one hand, the outer surface of the core 10 has residual alkali, the stability of the lithium supplement agent 1 is poor, and when the lithium supplement agent 1 is coated on the positive electrode of the battery, the lithium supplement agent 1 is more likely to cause gelation of the slurry during the slurry preparation process, resulting in poor slurry fluidity, which affects the processing performance of the lithium supplement agent 1. On the other hand, the surface of the lithium supplement 1 usually contains a large amount of free lithium. A high free lithium content will deteriorate the high-temperature storage performance of the battery, leading to problems such as flatulence and performance degradation during battery storage.

[0074] In the present application, on the one hand, the chemical formula of the first material phase 11 in the core 10 is configured as Li 5a+2b Fe a M b O 4a+2bWhile reducing the residual alkalinity value on the outer surface of the core 10, the coating layer 20 is then applied to the outer surface of the core 10, further reducing the residual alkalinity value of the lithium supplement 1 and improving its stability and processing performance. Furthermore, the coating layer 20 effectively isolates the first material phase 11 from moisture, oxygen, and other factors, enhancing the structural stability of the lithium supplement 1 and ensuring that the lithium supplement 1 can achieve stable lithium replenishment. Furthermore, the coating layer 20 reduces the free lithium content on the outer surface of the lithium supplement 1, facilitating its storage.

[0075] In the present application, the reducing agent is formed directly during the preparation of the first material phase 11 and the coated carbon material, without the addition of an additional reducing agent, thereby simplifying the preparation steps of the lithium supplement agent 1. In addition, this method of forming the reducing agent allows the reducing agent to be tightly bonded to the first material phase 11, facilitating the reducing agent's ability to reduce gas production in the lithium supplement agent 1.

[0076] In one embodiment, the coating layer 20 includes at least one of an isolation coating layer, an ion conductor coating layer, an electronic conductor coating layer, a single-atom deposition layer, and an oxide nanofilm layer.

[0077] In one embodiment, the coating 20 is an isolation coating. The isolation coating isolates the core 10 from moisture and carbon dioxide. The isolation coating protects the core 10 and improves its stability, ensuring its lithium replenishment function. It also ensures the stability and uniformity of the lithium replenishment agent 1 within the electrode active slurry and active layer, as well as good processing properties. The isolation coating may be located on a portion of the outer surface of the core 10 or may cover the entire outer surface of the core 10, as is not limited in this application.

[0078] In one embodiment, the isolation coating layer comprises at least one of a ceramic material, a polymer, and a carbon material. The ceramic comprises at least one of alumina, silica, boehmite, silicon nitride, silicon carbide, and boron nitride. The polymer comprises one or more of polyvinylidene fluoride, sodium alginate, sodium carboxymethyl cellulose, polyacrylic acid, polyacrylic acid salt, polyacrylonitrile, polyamide, polyimide, polyvinyl pyrrolidone, polyethylene oxide (PEO), polypyrrole (PPy), polytetrafluoroethylene (PTFE), and polyurethane (PU). The carbon material comprises at least one of graphene, carbon nanotubes, carbon nanospheres, carbon nanofibers, graphite, and carbon black.

[0079] In one embodiment, the coating 20 is an ion conductor coating. The ion conductor coating can enhance the ionic conductivity of the lithium supplement 1. The ion conductor coating facilitates the outward transport of lithium ions from the lithium supplement 1; it also assists in enhancing ion transport within the electrode. The ion conductor coating can have a dense or loose structure and can fully or partially coat the outer surface of the core 10.

[0080] In one embodiment, the material of the ion conductor coating layer includes at least one of a perovskite type, a NASICON type, a garnet type or a polymer type solid electrolyte. 3x La 2 / 3-x TiO3(LLTO), specifically Li 0.5 La 0.5 TiO3、Li 0.33 La 0.57 TiO3、Li 0.29 La 0.57 TiO3、Li 0.33 Ba 0.25 La 0.39 TiO3、(Li 0.33 La 0.56 ) 1.005 Ti 0.99 Al 0.01 O3、Li 0.5 La 0.5 Ti 0.95 Zr 0.05 At least one of O3, etc. NASICON type such as but not limited to Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP). Garnet type includes Li7La3Zr2O 12 (LLZO), Li 6.4 La3Zr 1.4 Ta 0.6 O 12 , Li 6.5 La3Zr 1.5 Ta 0.5 O 12 At least one of the polymer solid electrolytes includes at least one of PEO / PPO / PVDF etc. which dissolves lithium salt.

[0081] In one embodiment, the coating 20 is an electronic conductor coating. The electronic conductor coating can enhance the electronic conductivity of the lithium supplement 1. The electronic conductor coating helps reduce the internal impedance of the electrode and also serves as a conductive agent within the electrode. The electronic conductor coating can have a dense or loose structure and can fully or partially coat the outer surface of the core 10.

[0082] In one embodiment, the electronic conductor coating layer comprises at least one of a carbon material, a conductive polymer, or a conductive oxide. The carbon material includes at least one of graphene, carbon nanotubes, carbon nanospheres, carbon nanofibers, graphite, and carbon black. The conductive polymer may be, but is not limited to, the conductive polymer contained in the aforementioned isolation coating layer. The conductive oxide includes at least one of In2O3, ZnO, and SnO2.

[0083] In one embodiment, the coating layer 20 is a deposition layer, and the deposition layer includes a single atomic deposition layer and / or an oxide nanofilm layer obtained by atomic layer deposition technology. Specifically, the deposition layer can be a single atomic deposition layer obtained by atomic layer deposition technology, and the level can be a single atomic layer or nanolayer composed of atoms or molecules. Optionally, when the deposition layer is a single atomic deposition layer, different atomic deposition agents can be selected according to the different materials thereof, including but not limited to one or more of trimethylaluminum, triethylaluminum, triisobutylaluminum, tetrakis(diethylamino)titanium, triethylsilane, tetraethylsilane, and tetrakis(ethylmethylamino)zirconium.

[0084] Alternatively, the deposited layer may be an oxide nanofilm. For example, the oxide nanofilm may be formed by reacting the aforementioned monoatomic deposition layer with oxygen, and may be made of materials such as aluminum oxide, titanium dioxide, silicon dioxide, or zirconium dioxide. Alternatively, a nanoscale oxide layer may be formed directly on the outer layer of the core using vapor deposition technology. Of course, the oxide nanofilm may also be formed using other techniques.

[0085] In one embodiment, the coating layer 20 includes at least two of an isolation coating layer, an ion conductor coating layer, and an electron conductor coating layer. For example, in one embodiment, the coating layer 20 includes an isolation coating layer and an ion conductor coating layer, wherein the ion conductor coating layer is coated on the outer surface of the core 10, and the isolation coating layer is coated on the outer surface of the ion conductor coating layer.

[0086] In one embodiment, the coating layer 20 includes an isolation coating layer and an electronic conductor coating layer, wherein the isolation coating layer is coated on the outer surface of the core 10 , and the electronic conductor coating layer is coated on the outer surface of the isolation coating layer.

[0087] In one embodiment, the coating 20 includes an isolation coating, an ion conductor coating, and an electronic conductor coating (as shown in Figure 1), and the ion conductor coating is coated on the outer surface of the core 10, the isolation coating is coated on the outer surface of the ion conductor coating, and the electronic conductor coating is coated on the outer surface of the isolation coating.

[0088] In one embodiment, when the coating layer 20 includes two or more coating layers 20 , the coating order between the coating layers 20 can be set as needed and is not limited to the types listed above.

[0089] In one embodiment, the mass ratio of the core 10 to the coating 20 is 100:(0.01-15). That is, the ratio of the sum of the masses of the first material phase 11 and the second material phase 12 to the mass of the coating 20 is 100:(0.01-15). The mass ratio of the core 10 to the coating 20 affects the performance of the lithium supplement 1. If the content of the coating 20 is too low, the coating 20 will have a weak effect, and it will be difficult for the coating 20 to isolate the core 10 from the external environment, and it will not be able to play a good role in protecting the core 10 and improving the electronic conductivity or ionic conductivity of the lithium supplement 1. If the content of the coating 20 is too high, the interfacial resistance of the core 10 will be increased, and the proportion of lithium-rich material in the lithium supplement 1 will be reduced, thereby reducing the amount of lithium supplementation. In addition, it will also increase the processing difficulty of the lithium supplement 1.

[0090] In this embodiment, the mass ratio of the core 10 to the coating layer 20 is controlled within the range of 100:(0.01-15). This appropriate coating layer 20 mass ratio, on the one hand, improves the processing properties of the lithium supplement 1, enhances the bonding strength between the coating layer 20 and the core 10, and reduces the interfacial resistance of the core 10. On the other hand, the coating layer 20 does not excessively increase the mass of the lithium supplement 1, preventing excessive mass of the coating layer 20 from affecting the energy density and capacity of the lithium supplement 1. Furthermore, the coating layer 20 can better isolate the core 10 from the external environment, thereby protecting the core 10 and improving the electronic conductivity or ionic conductivity of the lithium supplement 1.

[0091] In one embodiment, the mass ratio of the core 10 to the coating layer 20 is 100:0.01, 100:0.05, 100:0.1, 100:0.5, 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, 100:11, 100:12, 100:13, 100:14 or 100:15.

[0092] In one embodiment, the mass ratio of the core 10 to the coating layer 20 is 100:(0.01-10). Within this range, the new performance of the lithium supplement 1 is more excellent. More preferably, the mass ratio of the core 10 to the coating layer 20 is 100:(0.01-5).

[0093] In one embodiment, the coating layer 20 has a thickness of 1 nm to 400 nm. The thickness of the coating layer 20 affects the performance of the lithium supplement 1. If the coating layer 20 is too thin, it is difficult for the coating layer 20 to isolate the core 10 from the external environment, and it cannot effectively protect the core 10 and improve the electronic conductivity or ionic conductivity of the lithium supplement 1. If the coating layer 20 is too thick, it will reduce the proportion of lithium-rich material in the lithium supplement 1, thereby reducing the amount of lithium supplementation. In addition, it will increase the interfacial resistance of the core 10 and increase the processing difficulty of the lithium supplement 1.

[0094] In this embodiment, the thickness of the coating layer 20 is controlled within the range of 1 nm to 400 nm. A suitable coating layer 20 thickness, on the one hand, improves the processing properties of the lithium supplement 1, enhances the bonding strength between the coating layer 20 and the core 10, and reduces the interfacial resistance of the core 10. On the other hand, the coating layer 20 does not excessively increase the mass of the lithium supplement 1, thus preventing excessive mass of the coating layer 20 from affecting the energy density and capacity of the lithium supplement 1. Furthermore, the coating layer 20 can better isolate the core 10 from the external environment, thereby protecting the core 10 and improving the electronic or ionic conductivity of the lithium supplement 1.

[0095] In one embodiment, the coating layer 20 has a thickness of 1 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, or 400 nm.

[0096] In one embodiment, the surface residual alkali value of the lithium supplement 1 is 0%-2%. The surface residual alkali value of the lithium supplement 1 affects its processing performance and stability. It is understood that the higher the surface residual alkali value of the lithium supplement 1, the stronger the alkalinity of the lithium supplement 1, the poorer the stability of the lithium supplement 1, and the lithium supplement 1 is more likely to react with air and electrolyte, directly affecting the electrochemical performance of the lithium supplement 1 and reducing battery safety. In addition, a high surface residual alkali value of the lithium supplement 1 can easily cause gelation of the lithium supplement 1 during slurry preparation, resulting in poor slurry fluidity, which seriously affects the processing performance of the lithium supplement 1.

[0097] The surface residual alkali value of the lithium supplement agent 1 provided in the present application is within the range of 0%-2%. The surface residual alkali value of the lithium supplement agent 1 is low, which improves the stability and processing performance of the lithium supplement agent 1, so that the lithium supplement agent 1 can achieve the function of efficient lithium supplementation.

[0098] In one embodiment, the surface residual alkali value of the lithium supplement agent 1 is 0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5% or 2%.

[0099] In one embodiment, the surface residual alkali value of the lithium supplement agent 1 is 0%-0.5%. Within this range, the performance of the lithium supplement agent 1 is even better.

[0100] In one embodiment, the lithium supplement 1 has a water absorption rate of less than 20 ppm / s in air at 25°C and 30%-35% relative humidity. The water absorption rate of the lithium supplement 1 affects the processing performance and stability of the lithium supplement 1. Generally, the greater the water absorption rate of the lithium supplement 1, the faster the lithium supplement 1 absorbs water vapor from the air. The lithium supplement 1 is highly susceptible to contact and reaction with ambient moisture, forming a large amount of residual alkali on the surface, making the lithium supplement 1 alkaline. When the residual alkali content is too high, the lithium supplement 1 has poor stability and is prone to reaction with air and electrolyte, directly affecting the electrochemical performance of the lithium supplement 1 and reducing battery safety.

[0101] In this embodiment, the water absorption rate of the lithium supplement agent 1 is less than 20 ppm / s in air at 25°C and 30%-35% relative humidity. The water absorption rate of the lithium supplement agent 1 is controlled to be low, ensuring that the lithium supplement agent 1 does not quickly absorb moisture in the air. This is beneficial to ensure that the lithium supplement agent 1 is effectively isolated from water vapor, protect the stability of the core 10, and ensure that the gram capacity of the lithium supplement agent 1 is fully utilized, thereby achieving efficient lithium supplementation.

[0102] In one embodiment, the water absorption rate of the lithium supplement agent 1 in air at 25° C. and 30%-35% relative humidity is 20 ppm / s, 19 ppm / s, 18 ppm / s, 17 ppm / s, 16 ppm / s, 15 ppm / s, 14 ppm / s, 13 ppm / s, 12 ppm / s, 11 ppm / s, 10 ppm / s, 9 ppm / s, 8 ppm / s, 7 ppm / s, 6 ppm / s, 5 ppm / s, 4 ppm / s, 3 ppm / s, 2 ppm / s, or 1 ppm / s.

[0103] In one embodiment, the water absorption rate of the lithium supplement agent 1 is less than 10 ppm / s in air at 25° C. and 30%-35% relative humidity. Under this condition, the performance of the lithium supplement agent 1 is even better.

[0104] In one embodiment, the lithium supplement agent has a water absorption rate of less than 10 ppm / s at 25°C and 20%-25% relative humidity. The water absorption rate of the lithium supplement agent 1 affects the processing performance and stability of the lithium supplement agent 1. In this embodiment, controlling the water absorption rate of the lithium supplement agent 1 to a low level ensures that the lithium supplement agent 1 does not rapidly absorb moisture from the air. This effectively isolates the lithium supplement agent 1 from water vapor, protects the stability of the core 10, and ensures the full gram capacity of the lithium supplement agent 1, thereby achieving efficient lithium supplementation.

[0105] In one embodiment, the water absorption rate of the lithium supplement agent 1 in air at 25° C. and 20%-25% relative humidity is 10 ppm / s, 9 ppm / s, 8 ppm / s, 7 ppm / s, 6 ppm / s, 5 ppm / s, 4 ppm / s, 3 ppm / s, 2 ppm / s or 1 ppm / s.

[0106] In one embodiment, the water absorption rate of the lithium supplement agent is less than 5 ppm / s at 25° C. and 20%-25% relative humidity. Under this condition, the performance of the lithium supplement agent 1 is even better.

[0107] In one embodiment, the water absorption test method is as follows:

[0108] First, control the room humidity at 25°C, 20-25% or 30-35% relative humidity.

[0109] Second, take out 0.3-0.5g of sample from the glove box, one sample at a time, and take out another sample from the glove box after the test.

[0110] Third, place the weighing bottle in an analytical balance with a precision of 1 / 100,000, close the hatch, and reset to zero.

[0111] Fourth, weigh 0.17-0.19 g of the sample to be tested into the container. Use a spoon to spread the material. Close the hatch. After stabilizing for 3-5 seconds, start the timer and record the mass on the analytical balance as the value at 0 min. Next, record the values ​​at 5 min, 10 min, 15 min, and 20 min, and calculate the average absorption data for 10-20 minutes.

[0112] Calculation formula:

[0113] Unit: ppm / s. Where t1 and t2 represent time, w0 represents initial mass, w t1 represents the mass at t1, w t2 represents the mass at t2.

[0114] In one embodiment, the particle size D50 of the lithium supplement 1 is 0.6 μm-40 μm. The particle size D50 refers to the particle size corresponding to when the cumulative particle size distribution percentage of the lithium supplement 1 reaches 50%.

[0115] It is understandable that if the particle size of the lithium supplement agent 1 is too small, the lithium supplement agent 1 is likely to agglomerate, making it difficult for the lithium inside the lithium supplement agent 1 to escape when replenishing active lithium to the negative electrode, thereby reducing the lithium replenishment effect of the lithium supplement agent 1; and if the particle size of the lithium supplement agent 1 is too large, it is not conducive to the electronic and ionic conduction of the lithium supplement agent 1, and is not conducive to the preparation of the slurry of the lithium supplement agent 1. When the lithium supplement agent 1 is coated on the positive electrode of the battery, the large particle size easily scratches the aluminum foil, which is not conducive to the preparation of the positive electrode sheet with the lithium supplement agent 1.

[0116] In this embodiment, the particle size D50 of the lithium supplement 1 is controlled between 0.6 μm and 40 μm, which ensures the rapid release of lithium ions while improving the dispersibility of the lithium supplement 1, facilitating the use of the lithium supplement 1 and protecting the electrode.

[0117] In one embodiment, the particle size D50 of the lithium supplement agent 1 can be 0.6 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm or 40 μm.

[0118] In one embodiment, the particle size D50 of the lithium supplement agent 1 is 3 μm-15 μm. Within this range, the performance of the lithium supplement agent 1 is even better.

[0119] In one embodiment, the specific surface area of ​​the lithium supplement 1 is 0.1 m 2 / g-20m 2 / g. In one embodiment, the specific surface area is measured using the BET (Brunauer-Emmett-Teller) specific surface area test method, and the specific surface area is the BET specific surface area. It is understood that if the specific surface area of ​​the lithium supplement agent 1 is too small, it will not be conducive to improving the conductivity and lithium ion extraction and insertion capabilities of the lithium supplement agent 1, thereby affecting the lithium ion transmission rate. If the specific surface area of ​​the lithium supplement agent 1 is too large, the density of the lithium supplement agent 1 is generally low, the volumetric energy density is low, and the coating difficulty is increased.

[0120] In this embodiment, the specific surface area of ​​the lithium supplement agent 1 is controlled to be 0.1 m 2 / g-20m 2 / g range, not only can the conductivity and lithium ion extraction and insertion capabilities of the lithium supplement agent 1 be improved, but also the volume energy density of the lithium supplement agent 1 can be increased, making the preparation of the lithium supplement agent 1 easier.

[0121] In one embodiment, the specific surface area of ​​the lithium supplement agent 1 can be 0.1 m 2 / g, 0.5m 2 / g、1m 2 / g, 2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m2 / g、8m 2 / g、9m 2 / g、10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g、15m 2 / g、16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g or 20m 2 / g.

[0122] The present application provides a method for preparing a lithium supplement 1. The method for preparing the lithium supplement 1 is used to prepare the lithium supplement 1 described above. The method for preparing the lithium supplement 1 includes steps S1, S2, and S3. The specific steps are as follows:

[0123] Step S1, adding a lithium source, an iron source and an M source to a complexing agent solution and stirring to obtain a gel;

[0124] Step S2, sintering the gel in a protective atmosphere to obtain a first material phase 11;

[0125] In step S3 , the first material phase 11 is mixed with a reducing agent and sintered to obtain a lithium supplementing agent 1 .

[0126] In one embodiment, the preparation method of the lithium supplement agent 1 further includes step S4: mixing the lithium supplement agent 1 in step S3 with a coating material, and sintering the mixture under a protective atmosphere to obtain a coated lithium supplement agent 1.

[0127] In step S1, a lithium source, an iron source, and a M source are added to a complexing agent solution to form a gel. The lithium source, iron source, and M source in the gel are uniformly mixed and well dispersed, facilitating the formation of an ordered structure during subsequent sintering. In one embodiment, in step S1, the mixture of the lithium source, iron source, M source, and complexing agent can be stirred under low-temperature heating conditions to facilitate the dissolution of the lithium source, iron source, and M source, and at least a portion of the solution is evaporated to facilitate the formation of a gel. Exemplarily, the heating temperature can be 60°C to 90°C.

[0128] In step S2, the gel is sintered under a protective atmosphere to prevent the M source from being oxidized. In one embodiment, a protective gas is introduced in step S2 to control the oxygen content to be below 50 ppm. The lithium source, iron source, and M source react at high temperature to generate a chemical formula of Li 5a+2b Fe a M b O 4a+2b The first material phase 11.

[0129] In step S3, the first material phase 11 and the reducing agent are mixed evenly and then sintered, and the reducing agent forms a second material phase 12. The second material phase 12 in the lithium supplement 1 is tightly combined with the first material.

[0130] In step S4, the coating material is a material capable of forming an isolation coating layer, an ion conductor coating layer, or an electronic conductor coating layer. Sintering the first material phase 11, the second material phase 12, and the coating material under a protective atmosphere prevents oxidation of the M element. In one embodiment, a protective gas is introduced in step S3 to control the oxygen content to below 50 ppm.

[0131] In one embodiment, when the coating material is carbon, a carbon layer is formed on the outer surfaces of the first material phase 11 and the second material phase 12. Specifically, a carbon layer is formed on the outer surface of the core 10. A method for forming the carbon layer includes the following steps: dispersing the core 10 in a carbon source, and forming a carbon layer on the surface of the core 10 after a carbonization treatment.

[0132] In one embodiment, after obtaining the gel in step S1, the gel is dried. During the drying process, the iron compound precipitates first to form a seed crystal, and grows into a core. After drying to a certain extent, the iron and M compounds precipitate together to form a coating layer. After drying, it is calcined at 300-700°C to obtain a precursor, in which the first material phase 11 in the precursor is combined with the outer surface of the second material phase 12.

[0133] In one embodiment, the preparation method of the lithium supplement 1 further includes a step of doping with metal elements, specifically as follows: the obtained precursor is crushed and placed in anhydrous ethanol, and a surface doping element compound is added while stirring, and the mixture is dried while stirring. After drying, the mixture is calcined at 800° C. to obtain a material core with a surface coated with the doping element.

[0134] The present application synthesizes a new lithium supplement agent 1 by using a sol-gel method. The first material phase of the lithium supplement agent 1 contains a variety of heterogeneous elements, has high purity, low surface residual alkalinity value, and high lithium supplement capacity. Its structure is more stable and can effectively reduce the release of oxygen species, thereby reducing the generation of gas. In addition, the coating layer contained on the surface can effectively isolate moisture, oxygen, etc. from contact with the lithium supplement agent 1, thereby improving the structural stability of the lithium supplement agent 1 and achieving a stable lithium supplement effect. At the same time, the second material phase is used as a reducing agent to combine with oxygen to form a stable substance, further reducing gas production and improving material stability; further, it can also improve the electronic and ion conductivity of the new lithium supplement agent and increase the rate of lithium ion release during charging. The lithium supplement agent 1 provided in the present application has more excellent performance.

[0135] In one embodiment, the sintering temperature of the gel is 400° C.-1000° C., and the sintering time is 3 h-20 h.

[0136] In one embodiment, the core 10 and the coating material are sintered at a temperature of 500° C. to 800° C. for a time of 1 hour to 10 hours.

[0137] In one embodiment, the lithium source is one or more of lithium oxide, lithium hydroxide, lithium acetate, lithium carbonate, lithium fluoride, and lithium chloride.

[0138] In one embodiment, the iron source is one or more of ferric acetate, ferric nitrate, ferric sulfate, ferric hydroxide, ferric chloride, and ferric oxide.

[0139] In one embodiment, the manganese source is one or more of manganese acetate, manganese nitrate, manganese monoxide, manganese sulfate, manganese hydroxide, and manganese dichloride.

[0140] In one embodiment, the M source is a nickel source, and the nickel source is one or more of nickel acetate, nickel nitrate, nickel oxide, nickel sulfate, nickel hydroxide, and nickel chloride.

[0141] In one embodiment, the complexing agent is at least one of citric acid, ammonium citrate, maleic acid, oxalic acid, ammonium oxalate, ascorbic acid, polyethylene glycol, polyvinyl pyrrolidone, glycerol, isopropanolamine, hydrogen peroxide, and the like.

[0142] In one embodiment, the complexing agent solution is a solution formed by dissolving the complexing agent in a solvent, wherein the solvent is one or more of methanol, glycerol, ethanol and water.

[0143] In one embodiment, the protective atmosphere is one or more of nitrogen, helium, argon, and neon.

[0144] In one embodiment, the preparation method of the lithium supplement agent 1 can also be: Li 5a+2b Fe a M b O 4a+2b The mixture is mixed with a reducing agent, ball-milled, and sintered at 200° C.-400° C. in a protective atmosphere for 3 h-20 h to obtain a lithium supplement agent 1.

[0145] The present application provides a positive electrode plate, which includes the lithium supplement agent 1 as described above, or includes the lithium supplement agent 1 prepared by the preparation method of the lithium supplement agent 1 as described above.

[0146] The present application provides a secondary battery, which includes a negative electrode plate, a separator, and the positive electrode plate as described above.

[0147] In one embodiment, the secondary battery is a lithium-ion battery, and the initial lithium desorption capacity of the lithium supplement agent 1 is greater than or equal to 500 mAh / g. The higher initial lithium desorption capacity of the lithium supplement agent 1 can achieve a better lithium supplement effect.

[0148] In one embodiment, the ratio of the first-cycle gas production of the lithium supplement 1 to the first-cycle gas production of the corresponding Li5FeO4 is 1%-30%. Compared with Li5FeO4, the first-cycle gas production of the lithium supplement 1 provided in this application is lower, thereby improving battery safety and electrochemical performance.

[0149] In one embodiment, the ratio of the first-cycle gas production of the lithium supplement 1 to the first-cycle gas production of the corresponding Li5FeO4 is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%.

[0150] In order to illustrate the beneficial effects of the method of the present application, the present application also provides the following examples and comparative examples:

[0151] Example 1

[0152] Example 1 provides a lithium supplement agent, which includes a first material phase and a second material phase. The first material phase includes a lithium-rich material, which is Li5FeO4. The second material phase includes a reducing agent, which is Al2S3. The mass ratio of the second material phase to the first material phase is 5%.

[0153] The preparation method of the lithium supplement in Example 1 comprises the following steps:

[0154] Step 1: dissolving a citric acid complexing agent in an anhydrous ethanol solution, and then dissolving lithium hydroxide: ferric acetate: nickel acetate in a molar ratio of 7:1:1, and stirring the solution at 60-90° C. until a dry gel is formed.

[0155] Step 2: sinter the dry gel prepared in step 1 at 750° C. under a protective atmosphere with the oxygen content controlled below 50 ppm for 3-20 hours to prepare a first material phase.

[0156] Step 3: Evenly mix the first material phase prepared in step 2 with 5% of a reducing agent, and sinter the mixture at 500° C.-800° C. under a protective atmosphere to obtain a lithium supplement.

[0157] The EDS and SEM spectra of the lithium supplement agent in Example 1 are shown in Figures 2 and 3, and the EDS spectra of C, O, Al, S, and Fe in the lithium supplement agent are shown in Figures 4, 5, 6, 7, and 8, respectively. In the lithium supplement agent in Example 1, Al2S3 exists on the surface of Li5FeO4.

[0158] Example 2

[0159] Example 2 provides a lithium supplement, which differs from the structure of Example 1 in that, in Example 2, the addition amount of the second material phase is 15%.

[0160] Example 3

[0161] Example 3 provides a lithium supplement, which differs from the structure of Example 1 in that, in Example 3, the addition amount of the second material phase is 3%.

[0162] Example 4

[0163] Example 4 provides a lithium supplement agent. The structure of Example 1 differs in that Example 4 further includes a coating layer, and the coating layer is a carbon material. The preparation method of Example 4 comprises: uniformly mixing the lithium supplement agent prepared in step 3 of Example 1 with a carbon source, and sintering the mixture at 200°C to 400°C under a protective atmosphere to obtain a carbon-coated lithium supplement agent.

[0164] Example 5

[0165] Example 5 provides a lithium supplement, which differs from the structure of Example 1 in that, in Example 5, the reducing agent in the second material phase is NiO.

[0166] Example 6

[0167] Example 6 provides a lithium supplement agent, which is different from the structure of Example 1 in that, in Example 6, the lithium-rich material in the first material phase is Li 3.5 Fe 0.5 Ni 0.5 O3.

[0168] Comparative Example 1

[0169] Comparative Example 1 provides a lithium supplement agent, which differs from the structure of Example 1 in that Comparative Example 1 does not include a reducing agent.

[0170] Comparative Example 2

[0171] Comparative Example 2 provides a lithium supplement agent, which is different from the structure of Example 1 in that, in Comparative Example 2, the lithium-rich material in the first material phase is Li 3.5 Fe 0.5 Ni 0.5 O3, and does not include reducing agents.

[0172] Comparative Example 3

[0173] No lithium supplement is added to the subsequent positive electrode sheets.

[0174] The lithium supplement provided in the above examples and comparative examples were assembled into positive electrode sheets and lithium-ion batteries according to the following methods:

[0175] Positive electrode sheet: A lithium supplement and lithium iron phosphate are mixed in a mass ratio of 2:98 to obtain a mixture. The mixture is mixed with polyvinylidene fluoride and SP-Li in a mass ratio of 95:3:2 and ball-milled to obtain a positive electrode slurry. The positive electrode slurry is coated on the surface of aluminum foil, roll-pressed, and vacuum-dried at 110°C overnight to obtain a positive electrode sheet;

[0176] Negative electrode: graphite negative electrode;

[0177] Electrolyte: Ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7, and LiPF6 was added to form an electrolyte. The concentration of LiPF6 was 1 mol / L.

[0178] Diaphragm: Polypropylene microporous separator;

[0179] Lithium-ion battery assembly: preparation into battery soft pack.

[0180] Related performance tests

[0181] The electrochemical performance of each lithium-ion battery assembled in the above lithium-ion battery embodiment was tested as shown in Table 1, and the test conditions were as follows:

[0182] Constant current and constant voltage charging, the first cycle charge and discharge voltage is 2.0-4.3V, the current is 0.1C, and the cut-off current is 0.01C.

[0183] The relevant performance test results are shown in Table 1 below:

[0184] Table 1 Performance test results

[0185] It can be seen from Examples 1-6 and Comparative Example 3 that the addition of the lithium supplement can increase the initial charge capacity of the battery, which means that the lithium supplement provided in this application can improve battery performance.

[0186] It can be seen from Examples 1-5 and Comparative Example 1 that the gas production in Comparative Example 1 is much greater than that in Examples 1-5, indicating that adding a reducing agent to the lithium supplement can effectively reduce the gas production of the lithium supplement and improve the safety performance of the battery.

[0187] It can be seen from Examples 1-3 that the greater the amount of reducing agent added, the smaller the gas production of the lithium supplement agent, and the initial charge gram capacity does not change much. Although the lithium supplement gram capacity decreases, it still maintains a high level.

[0188] It can be seen from Example 1 and Example 4 that adding a carbon coating layer is beneficial to improving the lithium replenishing gram capacity of the lithium replenishing agent.

[0189] It can be seen from Example 1 and Example 5 that, compared with NiO, when Al2S3 is used as the reducing agent, the gas production of the lithium supplement agent is the lowest, indicating that Al2S3 can better reduce the gas production of the lithium supplement agent.

[0190] It can be seen from Example 1 and Example 6 that Example 6 has a lower gas production, indicating that doping Li5FeO4 with reducing metal elements can reduce the gas production of the lithium supplement.

[0191] It can also be seen from Comparative Examples 1-2 that Comparative Example 2 has a lower gas production, indicating that doping Li5FeO4 with reducing metal elements can reduce the gas production of the lithium supplement.

[0192] The lithium supplement agent and its preparation method, positive electrode sheet and secondary battery provided in the embodiments of the present application are introduced in detail above. Specific examples are used herein to illustrate the principles and embodiments of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for those skilled in the art, according to the ideas of the present application, there may be changes in the specific embodiments and application scope. In summary, the content of this specification should not be understood as limiting the present application.

Claims

1. A lithium supplement, characterized in that: The lithium supplement agent includes a first material phase and a second material phase, the first material phase includes a lithium-rich material, and the second material phase includes a reducing agent.

2. The lithium supplement according to claim 1, characterized in that: The first material phase is Li 5a+2b Fe a M b O 4a+2b , wherein 0≤a≤1, 0≤b≤1, a and b are not 0 at the same time; M is a metal element; and / or The reducing agent includes at least one of AlN, FeS, S, Fe2S3, Al2S3, Li2S, NiO, and MnO.

3. The lithium supplement according to claim 2, characterized in that: a+b=1; and / or a>b.

4. The lithium supplement according to claim 2, characterized in that: The metal element includes at least one of divalent nickel, divalent manganese, divalent iron, and divalent cobalt.

5. The lithium supplement according to claim 1, characterized in that: The second material phase fills the gaps between the first material phases; or The second material phase is doped with the first material phase; or The second material is bonded to an outer surface of the first material phase.

6. The lithium supplement according to claim 1, characterized in that: The mass ratio of the second material phase to the first material phase is 1%-20%.

7. The lithium supplement according to claim 1, characterized in that: The lithium supplement further includes a coating layer, and the coating layer is coated on at least a portion of the outer surface of the first material phase and / or the second material phase.

8. The lithium supplement according to claim 7, characterized in that: The coating layer includes at least one of an isolation coating layer, an ion conductor coating layer, and an electronic conductor coating layer.

9. The lithium supplement according to claim 7, characterized in that: The coating layer is a deposition layer.

10. The lithium supplement according to claim 9, characterized in that: The deposited layer includes a single atomic deposition layer and / or an oxide nanofilm layer obtained by atomic layer deposition technology.

11. The lithium supplement according to claim 7, characterized in that: The ratio of the sum of the masses of the first material phase and the second material phase to the mass of the coating layer is 100:(0.01-15).

12. The lithium supplement according to claim 7, characterized in that: The coating layer has a thickness of 1 nm to 400 nm.

13. The lithium supplement according to claim 1, characterized in that: The surface residual alkali value of the lithium supplement agent is 0%-2%.

14. The lithium supplement according to claim 1, characterized in that: The water absorption rate of the lithium supplement agent is less than 20 ppm / s in air at 25°C and 30%-35% relative humidity; and / or At 25° C. and 20%-25% relative humidity in air, the water absorption rate of the lithium supplement agent is less than 10 ppm / s.

15. The lithium supplement according to claim 1, characterized in that: The particle size D50 of the lithium supplement agent is 0.6 μm-40 μm.

16. The lithium supplement according to claim 1, characterized in that: The specific surface area of ​​the lithium supplement is 0.1 m 2 / g-20m 2 / g.

17. A method for preparing a lithium supplement, characterized in that: The preparation method of the lithium supplement comprises: Adding lithium source, iron source and M source into the complexing agent solution and stirring to obtain a gel; sintering the gel in a protective atmosphere to obtain a first material phase; The first material phase is mixed with a reducing agent, and sintered to obtain the lithium supplement agent.

18. A positive electrode plate, characterized in that: The positive electrode plate includes the lithium supplement agent according to any one of claims 1 to 16, or includes the lithium supplement agent prepared by the preparation method of the lithium supplement agent according to claim 17.

19. A secondary battery, characterized in that: The secondary battery comprises a negative electrode sheet, a separator and the positive electrode sheet as claimed in claim 18.

20. The secondary battery according to claim 19, characterized in that: The secondary battery is a lithium-ion battery, in which the initial lithium desorption capacity of the lithium supplement agent is greater than or equal to 500 mAh / g; and / or The ratio of the first-cycle gas production of the lithium supplement agent to the first-cycle gas production of the corresponding Li5FeO4 is 1%-30%.

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