Manganese-based lithium supplement material, positive electrode lithium supplement additive, and preparation method and application thereof

Abstract

The present application discloses a manganese-based lithium supplement material, a positive electrode lithium supplement additive, and a preparation method and application thereof. The manganese-based lithium supplement material of the present application comprises at least Li2Mn as the main phase. 1 O2·xLi2O (0≤x≤2) and Mn as a secondary phase a 2 O b , and Mn a 2 O b It is combined with Li2Mn 1 The surface of O2·xLi2O, where Mn a 2 O b a is 1-2, b is 2-3. The positive electrode lithium supplement additive of the present application is a core-shell structure, and the core contains a manganese-based lithium supplement material. The manganese-based lithium supplement material contains Li2Mn 1 O2·xLi2O and Mn a 2 O b The main phase has a synergistic effect, giving the main phase small and uniform grains, and giving the manganese-based lithium supplement material high chemical stability, which can effectively inhibit or reduce the generation of gas during the initial cycle of the battery, and improve the battery's cycle performance and safety performance. In addition, the main phase is rich in lithium, giving the manganese-based lithium supplement material an excellent lithium supplement effect.

Description

Technical Field

[0001] The present application belongs to the field of secondary batteries, and specifically relates to a manganese-based lithium supplement material, a positive electrode lithium supplement additive, and a preparation method and application thereof. Background Art

[0002] During the first charging process of lithium-ion batteries, the negative electrode surface is usually accompanied by the formation of a solid electrolyte membrane SEI film, which consumes a large amount of Li + , which means that Li released from the positive electrode material + Part of it is irreversibly consumed, and the reversible specific capacity of the corresponding battery cell is reduced. For example, a large amount of active lithium will be converted into lithium carbonate, lithium fluoride and alkyl lithium, causing lithium loss in the positive electrode material, reducing the initial coulomb efficiency and battery capacity of the battery. Specifically, the negative electrode material, especially the silicon-based negative electrode material, will further consume Li + , the consumption of the positive electrode lithium source will be further aggravated, resulting in the first excessively low Coulombic efficiency.

[0003] In order to improve the low coulomb efficiency problem caused by irreversible loss of the negative electrode, in addition to pre-lithiation of the negative electrode material and the pole piece, lithium supplementation of the positive electrode can also achieve the requirement of high energy density. The current lithium nickel-based oxide lithium supplementation additive is used as a sacrificial positive electrode material. Although it can provide lithium ions for lithium supplementation during the charging process, it decomposes during the initial cycle of the battery and produces gas, which deteriorates the battery's cyclability and safety.

[0004] In addition, current lithium replenishing materials such as positive electrode lithium replenishing materials have the following defects: excessive activity, and they will react with moisture, carbon dioxide, etc. in the environment during storage, transportation and processing, resulting in the inability to stably store the positive electrode lithium replenishing materials or the negative electrode lithium replenishing materials for a long time. It will also reduce the lithium replenishing effect of the positive electrode lithium replenishing materials or the negative electrode lithium replenishing materials, or further lead to a reduction in processing performance, resulting in a reduction in the electrochemical performance of battery components such as the prepared electrode sheets, making the battery's first coulombic efficiency and battery capacity unsatisfactory. Summary of the invention

[0005] The purpose of this application is to overcome the above-mentioned shortcomings of the prior art and provide a manganese-based lithium supplement material, a positive electrode lithium supplement additive and a preparation method thereof, so as to reduce the gas production of the battery caused by the easy decomposition of existing positive electrode lithium supplement materials such as lithium nickel-based oxides and solve the technical problem of unsatisfactory processing performance.

[0006] Another object of the present application is to provide an electrode sheet and a secondary battery containing the electrode sheet to solve the technical problems of the existing secondary batteries having unsatisfactory first cycle performance and safety.

[0007] In order to achieve the above application objectives, the first aspect of the present application provides a manganese-based lithium supplement material. The manganese-based lithium supplement material of the present application at least comprises Li2Mn as the main phase 1 O2·xLi2O and Mn as a secondary phase a 2 O b , and Mn a 2 O b It is combined with Li2Mn 1 The surface of O2·xLi2O, where Mn a 2 O b Here a is 1-2 and b is 2-3.

[0008] Furthermore, Li2Mn 1 The mass content M1 of O2·xLi2O in the manganese-based lithium supplement material is 88%≤M1<100%.

[0009] Furthermore, Li2Mn 1 The particle size D50 of O2·xLi2O is 1-3 µm.

[0010] Furthermore, Mn a 2 O b The mass content M2 in the manganese-based lithium supplement material is 0<M2≤12%.

[0011] Furthermore, Mn a 2 O b The particle size D50 is 0.2-1.3 µm.

[0012] Furthermore, Mn a 2 O b Includes at least one of Mn2O3 and MnO2.

[0013] Furthermore, the first delithiation capacity of the manganese-based lithium supplement material is above 400 mAh / g.

[0014] In a second aspect of the present application, a method for preparing a manganese-based lithium-supplementing material is provided. The method for preparing a manganese-based lithium-supplementing material of the present application comprises the following steps:

[0015] Mixing a manganese source and a lithium source to obtain a mixture precursor;

[0016] The precursor mixture is first sintered in an oxygen-containing atmosphere to generate at least Li2Mn 1 O2·xLi2O and Mn as a secondary phase a 2 Ob , and Mn a 2 O b It is combined with Li2Mn 1 The surface of O2·xLi2O, where Mn a 2 O b Where a is 1-2, b is 2-3, and a manganese-based lithium supplement material is obtained.

[0017] Furthermore, the temperature of the first sintering treatment is 400-600° C. and the time is 4-8 hours.

[0018] Furthermore, the oxygen-containing atmosphere is an atmosphere composed of a mixture gas of a chemically inert gas and oxygen, and the volume concentration of oxygen in the mixture gas is 0.1%-1%.

[0019] Furthermore, the manganese source and the lithium source are mixed in a molar ratio of manganese to lithium of 1:2 to 1:2.4.

[0020] Further, the manganese source includes MnO.

[0021] Furthermore, the lithium source includes at least one of lithium oxide and LiOH.

[0022] In a third aspect of the present application, a positive electrode lithium supplement additive is provided. The positive electrode lithium supplement additive of the present application comprises a core body and an encapsulation layer covering the core body, the core body comprises a lithium supplement material, and the lithium supplement material is a manganese-based lithium supplement material of the present application or a manganese-based lithium supplement material prepared by the method for preparing a manganese-based lithium supplement material of the present application.

[0023] Furthermore, the thickness of the encapsulation layer is 2-10 nm.

[0024] Furthermore, the mass of the encapsulation layer accounts for 1%-5% of the total mass of the positive electrode lithium supplement additive.

[0025] Further, the encapsulation layer includes at least one of an ion conductor encapsulation layer and an electron conductor encapsulation layer.

[0026] Furthermore, lithium carbonate is dispersed in the encapsulation layer or at the interface between the encapsulation layer and the core body.

[0027] Furthermore, the capacity attenuation rate of the positive electrode sheet prepared by the positive electrode lithium supplement additive, the conductive agent and the binder stored for 20 hours at an ambient humidity of 25% relative to that stored for 0.5 hours is no more than 30%.

[0028] Furthermore, the capacity attenuation rate of the positive electrode sheet prepared by the positive electrode lithium supplement additive, the conductive agent and the binder stored for 20 hours at an ambient humidity of 10% relative to that stored for 0.5 hours is no more than 20%.

[0029] In a fourth aspect of the present application, a method for preparing a positive electrode lithium supplement additive is provided. The method for preparing a positive electrode lithium supplement additive of the present application comprises the following steps:

[0030] Providing a core material, wherein the core material contains the manganese-based lithium-supplementing material of the present application or the manganese-based lithium-supplementing material is prepared by the method for preparing the manganese-based lithium-supplementing material of the present application;

[0031] In a protective atmosphere, a packaging layer covering the core material is formed on the surface of the core material to obtain a positive electrode lithium supplement additive.

[0032] Furthermore, the method for forming an encapsulation layer covering the core material on the surface of the core material comprises the following steps:

[0033] In a protective atmosphere, the precursor of the encapsulation layer is mixed with the core material and then subjected to a second sintering process, wherein the second sintering process contains a first carbon source.

[0034] Or further, the method for forming an encapsulation layer covering the core material on the surface of the core material comprises the following steps:

[0035] After the step of forming an encapsulation layer covering the core material on the surface of the core material, the method further includes the step of heat treating the generated positive electrode lithium supplement additive in an environment containing a second carbon source.

[0036] In a fifth aspect of the present application, a positive electrode sheet is provided, which comprises a current collector and a positive electrode active layer bonded to the surface of the current collector, wherein the positive electrode active layer is doped with the manganese-based lithium supplement material of the present application or the positive electrode lithium supplement additive of the present application.

[0037] In a sixth aspect of the present application, a secondary battery is provided. The secondary battery of the present application comprises a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet of the present application.

[0038] Compared with the prior art, this application has the following technical effects:

[0039] The manganese-based lithium supplement material of this application is Li2Mn 1 O2·xLi2O as the main phase, with Mn a 2 O b As a secondary phase and combined with the surface of the main phase, the secondary phase can play a spatial barrier role and inhibit the grain growth of the main phase. 1 O2·xLi2O and Mn a 2 O bThe main phase has a synergistic effect, giving the main phase small and uniform grains, and giving the manganese-based lithium supplement material high chemical stability, which can effectively inhibit or reduce the generation of gas during the initial cycle of the battery, and improve the battery's cycle performance and safety performance. In addition, the main phase is rich in lithium, giving the manganese-based lithium supplement material an excellent lithium supplement effect.

[0040] The preparation method of the manganese-based lithium supplement material of the present application can effectively prepare the main phase Li2Mn 1 O2·xLi2O and secondary phase Mn a 2 O b The composite of Li2Mn 1 O2·xLi2O and Mn a 2 O b The two can play a synergistic role, making the main phase grains in the prepared manganese-based lithium-supplementing material small, improving the delithiation effect of the main phase, and giving the prepared manganese-based lithium-supplementing material excellent stability and lithium-supplementing effect. Moreover, the preparation method of the manganese-based lithium-supplementing material of the present application can ensure that the prepared manganese-based lithium-supplementing material has stable performance, high production efficiency, and saves production costs.

[0041] Since the core body contained in the positive electrode lithium supplement additive of the present application contains the manganese-based lithium supplement material of the present application, the core body has a high lithium removal effect, which gives the positive electrode lithium supplement additive of the present application an excellent lithium supplement effect, and can effectively inhibit or reduce the generation of gas during the initial cycle of the battery, thereby improving the cycle performance and safety performance of the battery. The encapsulation layer contained in the positive electrode lithium supplement additive of the present application can effectively protect the core body, so that the manganese-based lithium supplement material contained in the core body is isolated from moisture and carbon dioxide in the outside world, ensuring the stability of the core body, thereby ensuring the lithium supplement effect and stability of the positive electrode lithium supplement additive, and having good processing performance.

[0042] The preparation method of the positive electrode lithium supplement additive of the present application can effectively prepare a positive electrode lithium supplement additive with a core-shell structure, ensuring that the prepared positive electrode lithium supplement additive has excellent lithium supplement effect, stable lithium supplement performance and good processing performance. In addition, the preparation method of the positive electrode lithium supplement additive can ensure that the structure and electrochemical performance of the prepared positive electrode lithium supplement additive are stable, and the efficiency is high, saving production costs.

[0043] Since the positive electrode sheet of the present application contains the manganese-based lithium-supplementing material or positive electrode lithium-supplementing additive of the present application, the structure and chemical properties of the positive electrode sheet are stable during the initial cycle, which can effectively suppress or reduce the generation of gas, and improve the cycle performance and safety performance of the battery. At the same time, during the charging and discharging process, the manganese-based lithium-supplementing material or positive electrode lithium-supplementing additive contained therein can be used as a lithium source to efficiently delithiate during the first cycle of charging, providing abundant lithium ions to supplement the irreversible lithium ions consumed by the formation of the SEI film at the negative electrode, thereby maintaining the abundance of lithium ions in the battery system and improving the first efficiency and overall electrochemical performance of the battery. Moreover, when containing the positive electrode lithium-supplementing additive of the present application, the good processing performance of the positive electrode lithium-supplementing additive ensures the quality of the positive electrode sheet and improves the electrochemical performance of the positive electrode sheet.

[0044] Since the secondary battery of the present application contains the positive electrode sheet of the present application, the lithium-ion battery of the present application has excellent cycle performance and safety performance, and has excellent first coulomb efficiency, battery capacity and cycle performance, long life and stable electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0046] Figure 1 This is a schematic diagram of the process of preparing a manganese-based lithium supplement material according to an embodiment of the present application;

[0047] Figure 2 This is a schematic diagram of the structure of the positive electrode lithium supplement additive in the embodiment of the present application;

[0048] Figure 3 This is a schematic diagram of the process of preparing a positive electrode lithium supplement additive according to an embodiment of the present application;

[0049] Figure 4 An X-ray diffraction (XRD) diagram of a manganese-based lithium supplement material is provided for Example 1 of the present application. DETAILED DESCRIPTION

[0050] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0051] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0052] In this application, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0053] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0054] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0055] The weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also indicate the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass described in the embodiment description of the present application can be a mass unit known in the chemical industry such as µg, mg, g, kg, etc.

[0056] The terms "first" and "second" are used only for descriptive purposes to distinguish objects such as substances from each other, and should not be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0057] In a first aspect, the present invention provides a manganese-based lithium supplement material. The manganese-based lithium supplement material of the present invention at least comprises Li2Mn as a main phase. 1 O2·xLi2O (0≤x≤2) and Mn as a secondary phase a 2 O b .

[0058] Among them, the secondary phase Mn contained in the manganese-based lithium supplement material a 2 O b It is combined with Li2Mn 1 The surface of O2·xLi2O acts as a space barrier, inhibiting the grain growth of the main phase and increasing the Li2Mn 1 O2·xLi2O has a lithium removal capacity, thereby improving the lithium replenishment effect of manganese-based lithium replenishment materials. a 2 O b It is combined with Li2Mn 1 The surface of O2·xLi2O can make Mn a 2 O b With Li2Mn 1 O2·xLi2O play a synergistic role in giving the main phase Li2Mn 1 O2·xLi2O has small and uniform crystals and gives the manganese-based lithium supplement material high chemical stability. It can effectively inhibit or reduce the generation of gas during the initial cycle of the battery, thereby improving the cycle performance and safety performance of the battery.

[0059] In the secondary phase Mn a 2 O b In Mn, a is 1-2 and b is 2-3. a 2 O b In Mn 2 The valence state of Mn can be +3 or +4. a 2 O b It may include at least one of Mn2O3 and MnO2.

[0060] After testing, the secondary phase Mn a 2 O b The particle size of the main phase Li2Mn 1 The particle size of O2·xLi2O is small, as shown in the embodiment, the secondary phase Mn a 2 O bThe D50 of the nanostructured carbon nanotubes is distributed in the range of 0.2-1.3 µm, further 0.4-1 µm, and specifically can be 0.2 µm, 0.3 µm, 0.4 µm, 0.5 µm, 0.6 µm, 0.7 µm, 0.8 µm, 0.9 µm, 1 µm, 1.1 µm, 1.2 µm, 1.3 µm and other typical but non-limiting particle sizes. It can be combined with the main phase Li2Mn 1 The surface of O2·xLi2O effectively acts as a space barrier, inhibiting the main phase Li2Mn 1 The crystal phase of O2·xLi2O grows.

[0061] Due to Mn a 2 O b As a secondary phase in manganese-based lithium-supplementing materials, it is a doped phase, and its content in manganese-based lithium-supplementing materials is higher than that of the main phase Li2Mn 1 The content of O2·xLi2O is low. In the embodiment, Mn a 2 O b The mass content M2 in the manganese-based lithium supplement material can be controlled to 0<M2≤12%, further 0<M2≤7%, and further 0<M2≤4%. a 2 O b The content in manganese-based lithium supplement materials fully exerts its spatial barrier effect on the main phase and inhibits the main phase Li2Mn 1 Based on the growth of O2·xLi2O particles, the main phase Li2Mn 1 The content of O2·xLi2O in the manganese-based lithium supplement material is used to improve the lithium supplement effect of the manganese-based lithium supplement material.

[0062] The main phase Li2Mn contained in manganese-based lithium supplement materials 1 Mn contained in O2·xLi2O 1 The valence state is +2. As the main phase in the manganese-based lithium supplement material, it plays the role of providing lithium ions. When it is used as a lithium supplement material, it can delithium during the first cycle of charging and act as a "sacrificial agent" to provide and release lithium ions to supplement the irreversible lithium ions consumed by the formation of the SEI film at the negative electrode, thereby ensuring the excellent lithium supplement effect of the manganese-based lithium supplement material in the embodiment of the present application.

[0063] Since Li2Mn 1 O2·xLi2O is the main phase in manganese-based lithium supplement materials. As the main component providing lithium ions, its content in manganese-based lithium supplement materials is higher than that of the secondary phase Mn a 2 O b In the case of high content of Li2Mn, as in the embodiment, the main phase is controlled 1The mass content M1 of O2·xLi2O in the manganese-based lithium supplement material is 88%≤M1<100%, so that the main phase is the main component of the manganese-based lithium supplement material, giving the manganese-based lithium supplement material a high lithium supplement effect.

[0064] In the embodiment, Li2Mn 1 O2·xLi2O contains x 0≤x≤2, therefore, x can be, but is not limited to, typical but non-limiting values ​​such as 0, 1, and 2. When x is 2, Li2Mn 1 O2·xLi2O is Li2Mn 1 O2·2Li2O, that is, Li6MnO4. When x is 0, Li2Mn 1 O2·xLi2O is Li2Mn 1 O2.

[0065] Due to the secondary phase Mn a 2 O b The existence of Li2Mn plays a role as a space barrier, inhibiting the grain growth of the main phase. 1 O2·xLi2O, such as Li6Mn 1 The particle size of O4 is smaller than that of existing manganese-based lithium supplement materials. 1 The particle size of O2·xLi2O is D50 distributed between 1-3 µm, and further distributed between 1.2-1.8 µm, and can be 1.2 µm, 1.3 µm, 1.4 µm, 1.5 µm, 1.6 µm, 1.7 µm, 1.8 µm, 1.9 µm, 20 µm, 2.2 µm, 2.3 µm, 2.4 µm, 2.5 µm, 2.7 µm, 2.8 µm, 2.9 µm, 3 µm, etc. Typical but non-limiting particle sizes. The main phase Li2Mn 1 O2·xLi2O has small and uniform grains, which effectively improves the chemical stability of manganese-based lithium-supplementing materials.

[0066] In addition, the Li2Mn in the manganese-based lithium supplement materials in the above embodiments 1 Mn in O2·xLi2O 1 With Mn a 2 O b Mn 2 Both represent the manganese element, the difference is that Mn 1 With Mn 2 The valence state is different, so it should not be understood as Mn 1 The expression of manganese with a valence state of +1 should not be understood as Mn 2 Describes the element manganese with a valence state of +2.

[0067] Therefore, the Li2Mn in the manganese-based lithium supplement materials in the above embodiments 1 O2·xLi2O and Mn a 2 O b The main phase is small and uniform in size, and the main phase and the secondary phase are combined in different ways. The main phase and the secondary phase are combined in different ways, and the manganese-based lithium-supplementing material is endowed with high chemical stability. During the initial cycle of the battery, the generation of gas can be effectively suppressed or reduced, and the cycle performance and safety performance of the battery can be improved. The main phase is rich in lithium, which gives the manganese-based lithium-supplementing material an excellent lithium-supplementing effect.

[0068] In the second aspect, the present application embodiment provides a method for preparing the manganese-based lithium supplement material in the above-mentioned embodiment. The process flow of the method for preparing the manganese-based lithium supplement material in the embodiment of the present application is as follows: Figure 1 As shown, the following steps are included:

[0069] Step S01: mixing a manganese source and a lithium source to obtain a mixture precursor;

[0070] Step S02: subjecting the precursor mixture to a first sintering treatment in an oxygen-containing atmosphere to obtain a manganese-based lithium supplementing material.

[0071] The manganese source in step S01 is the main phase Li2Mn contained in the manganese-based lithium supplement material of the above-mentioned embodiment of the application. 1 O2 and secondary phase Mn a 2 O b The lithium source is the main phase Li2Mn contained in the manganese-based lithium supplement material of the above-mentioned application embodiment. 1 In one embodiment, the manganese source may include MnO. The lithium source may include at least one of lithium oxide and LiOH.

[0072] Because in the above manganese-based lithium supplement materials, Li2Mn 1 O2 is the main phase, Mn a 2 O b As a secondary phase, therefore, the mixing ratio of the manganese source and the lithium source in step S01 should ensure that the Li2Mn generated in the manganese-based lithium supplement material generated in step S02 is 1 O2·xLi2O can be used as the main phase, Mn a 2 O b As a secondary phase. For example, in the embodiment, the manganese source and the lithium source are mixed in a ratio of 1:2 to 1:2.4. Specifically, the mixing process can be a typical but non-limiting ratio of 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, etc.

[0073] The first sintering treatment in step S02 is to sinter the mixture precursor in step S01 in an oxygen-containing atmosphere to generate the main phase Li2Mn contained in the above manganese-based lithium supplement material. 1 O2 and secondary phase Mn a 2 O b Therefore, in the manganese-based lithium supplement material generated in step S02, the secondary phase Mn a 2 O b It is combined with Li2Mn 1 The surface of O2.

[0074] In the embodiment, the temperature of the first sintering treatment can be 400-600 ° C, and can be 400 ° C, 430 ° C, 450 ° C, 480 ° C, 500 ° C, 530 ° C, 550 ° C, 580 ° C, 600 ° C, etc., which are typical but non-limiting temperatures. The time of the first sintering treatment should be sufficient, such as 4-8 h, and can be 4 h, 5 h, 6 h, 7 h, 8 h, etc., which are typical but non-limiting times. By controlling and optimizing the temperature and time of the first sintering treatment, the mixture precursor can fully react to generate the main phase Li2Mn 1 O2 and secondary phase Mn a 2 O b , and ensure that the secondary phase Mn a 2 O b It is combined with Li2Mn 1 The surface of O2 plays a spatial barrier role and improves the chemical stability of manganese-based lithium-supplementing materials.

[0075] In addition, the oxygen-containing atmosphere of the first sintering treatment has an effect on the secondary phase Mn a 2 O b The formation of the secondary phase Mn is also significantly affected. For example, in the embodiment, the oxygen-containing atmosphere is a mixture of a chemically inert gas and oxygen, and the volume concentration of oxygen in the mixture is 0.1%-1%. By adjusting the oxygen content in the oxygen-containing atmosphere and combining the conditions of the first sintering treatment, the secondary phase Mn a 2 O b The amount of secondary phase Mn a 2 O b The chemically inert gas in the oxygen-containing atmosphere can be but not limited to Ar gas.

[0076] Therefore, the preparation methods of the manganese-based lithium supplement materials in the above-mentioned embodiments can effectively prepare the main phase Li2Mn1 O2 and secondary phase Mn a 2 O b The secondary phase Mn a 2 O b It is combined with the main phase Li2Mn 1 The complex on the surface of O2 makes the Li2Mn 1 O2 and Mn a 2 O b The two can play a synergistic role, which can make the main phase grains in the prepared manganese-based lithium-supplementing material small, and give the prepared manganese-based lithium-supplementing material excellent stability and lithium-supplementing effect. Moreover, the preparation method of the manganese-based lithium-supplementing material in the embodiment of the present application can ensure that the prepared manganese-based lithium-supplementing material has stable performance, high production efficiency, and saves production costs.

[0077] In a third aspect, the present application provides a positive electrode lithium supplement additive. The present application embodiment positive electrode lithium supplement additive comprises a core body and an encapsulation layer coated on the core body, that is, the structure of the present application embodiment positive electrode lithium supplement additive is a core-shell structure. For example, in the embodiment, the structure of the present application embodiment positive electrode lithium supplement additive is as shown in Figure 2 As shown, it includes a core body 10 and a packaging layer 20 coated on the core body 10 .

[0078] Among them, the core 10 includes a lithium supplement material, and the lithium supplement material is the manganese-based lithium supplement material of the above text application embodiment. In this way, the core 10 serves as a lithium source for the positive electrode lithium supplement additive. During the first charge, the manganese-based lithium supplement material of the above text application embodiment contained in the core 10 can provide abundant lithium ions, so that it can be used as a "sacrificial agent" during the first cycle of charging, and release all the lithium ions contained in the positive electrode lithium supplement additive as much as possible at one time to supplement the irreversible lithium ions consumed by the negative electrode to form the SEI film, thereby ensuring the excellent lithium supplement effect of the positive electrode lithium supplement additive of the present application embodiment. Moreover, during the initial cycle of the battery, it can effectively suppress or reduce the generation of gas, and improve the cycle performance and safety performance of the battery.

[0079] In the embodiment, the particle size and morphology of the core body 10 may be determined by the particle size or morphology of the manganese-based lithium supplementing material.

[0080] On the basis of the core body 10 in the above embodiments, the encapsulation layer 20 contained in the positive electrode lithium supplement additive in the above embodiments is coated on the core body 10 to form a complete and dense coating layer. Therefore, the encapsulation layer 20 can effectively protect the core body 10, so that the core body 10, specifically the manganese-based lithium supplement material, is isolated from moisture and carbon dioxide in the outside world, ensuring the efficient lithium supplement effect and stability of the manganese-based lithium supplement material contained in the core body 10, and ensuring the stability and uniformity of lithium supplementation of the positive electrode lithium supplement additive in the positive electrode active slurry and active layer to improve the processing performance of the positive electrode lithium supplement additive, and avoid the presence of the positive electrode lithium supplement additive causing a sharp increase in the viscosity of the positive electrode active layer slurry and gelation.

[0081] Based on the above-mentioned role of the encapsulation layer 20, the encapsulation layer 20 should at least have the function of isolating moisture and carbon dioxide. For example, in the embodiment, the mass of the encapsulation layer 20 accounts for 1%-5% of the total mass of the positive electrode lithium supplement additive, which can be 1%, 2%, 3%, 4%, 5% and other typical but non-limiting proportions. By controlling the mass content of the encapsulation layer 20, the thickness range of the encapsulation layer 20 is indirectly controlled. For example, in the embodiment, the thickness of the encapsulation layer 20 is 2-10 nm. By controlling the mass content and / or thickness of the encapsulation layer 20, the encapsulation layer 20 can effectively fully cover the core 10, improve the protection of the core, and improve the lithium supplement stability and processability of the core. Correspondingly, the material of the encapsulation layer 20 can be a material that can form at least a material that has the function of isolating moisture and carbon dioxide, such as at least one of an oxide, a polymer or a carbon material.

[0082] Furthermore, since the encapsulation layer 20 is the surface of the core body 10, the lithium supplement material contained in the core body 10 needs to pass through the encapsulation layer 20 during the lithium ion release process during the first charge of lithium removal, so the thickness of the encapsulation layer 20 and other factors will affect the release and migration efficiency of lithium ions, and its electrochemical properties will also affect the release and migration efficiency of lithium ions. Therefore, the encapsulation layer 20 has good ionic conductivity characteristics on the basis of isolating unfavorable factors such as moisture and carbon dioxide. In an embodiment, the encapsulation layer 20 may include an ion conductor encapsulation layer.

[0083] Similarly, based on the encapsulation layer 20 covering the surface of the core 10, the conductivity of the positive electrode lithium supplement additive during or after the lithium supplementation process will also affect the electrochemical properties of the battery such as the rate and the first effect. Therefore, the encapsulation layer 20 can also have good electronic conductivity properties on the basis of isolating adverse factors such as moisture and carbon dioxide. In an embodiment, the encapsulation layer 20 can include an electronic conductor encapsulation layer.

[0084] Therefore, as an embodiment of the present application, the encapsulation layer 20 contained in the positive electrode lithium supplement additive may include at least one of an ion conductor encapsulation layer and an electronic conductor encapsulation layer. Therefore, the encapsulation layer 20 has at least the following structure:

[0085] In one embodiment, the encapsulation layer 20 includes an electronic conductor encapsulation layer, which is coated on the surface of the core body. The electronic conductor encapsulation layer can be a single layer or multiple layers. When the electronic conductor encapsulation layer is a single layer, it can be a conductive coating layer formed by a conductive material, or a mixture conductive coating layer formed by a mixture of multiple conductive materials. When the electronic conductor encapsulation layer is a multilayer, it can be a composite conductive layer formed by conductive material coating layers formed by different conductive materials.

[0086] When the encapsulation layer 20 is only provided with an electronic conductor encapsulation layer, it should at least meet the above-mentioned compactness characteristics, that is, at least be able to isolate water vapor or carbon dioxide in the environment to ensure the lithium replenishment stability and processing performance of the positive electrode lithium replenishment additive.

[0087] The electronic conductor packaging layer provided in the packaging layer 20 can enhance the electronic conductivity of the packaging layer 20, thereby enhancing the electronic conductivity of the positive electrode lithium supplement additive, which is beneficial to reducing the impedance inside the electrode; at the same time, during the release process of the core body 10 as a "sacrifice" and after the release, the electronic conductor packaging layer can also be reused to play an auxiliary role as a conductive agent inside the positive electrode.

[0088] In the embodiment, the material of the electronic conductor encapsulation layer includes at least one of a carbon material, a conductive polymer or a conductive oxide. In a specific embodiment, the carbon material includes at least one of amorphous carbon, carbon nanotubes, graphite, carbon black, graphene, etc. In a specific embodiment, the conductive oxide may include at least one of In2O3, ZnO, SnO2. By adjusting the material of the electronic conductor encapsulation layer, its electronic conductivity can be further improved. In a specific embodiment, the conductive polymer includes [C6H7O6Na] n Organic polymers with the structure [C6H7O2(OH)2OCH2COONa] n Organic polymers with the structure [C3H4O2] n Organic polymers with the structure [C3H3O2M a ] n Organic polymers with [C3H3N] n An organic polymer with the structure -[CH2-CF2] n -structure, an organic polymer containing -[NHCO]-structure, an organic polymer containing an imide ring -[CO-N-CO]-structure on the main chain, and one or more of polyvinylpyrrolidone, wherein Ma Alkali metal elements. In some embodiments of the present application, the polymer includes 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). In some embodiments of the present application, the polymer includes one or more of sodium carboxymethyl cellulose and polyacrylic acid. Sodium carboxymethyl cellulose and polyacrylic acid are two-dimensional surface polymers with good adhesion, which can effectively coat the core of the manganese-based lithium supplement material, thereby avoiding the contact between the core of the manganese-based lithium supplement material and the air, and improving the stability of the positive electrode lithium supplement additive. In an embodiment of the present application, the molecular weight of the polymer is greater than or equal to 100,000. The molecular weight of the polymer can be, but is not limited to, 100,000, 150,000, 200,000, 300,000, 500,000 or 1 million. The larger the molecular weight of the polymer, the higher the density and structural strength of the polymer layer, and the more conducive to the protection of the core 10.

[0089] In another embodiment, the encapsulation layer 20 includes an ion conductor encapsulation layer, which is coated on the surface of the core. The ion conductor encapsulation layer can be a single layer or multiple layers. When the ion conductor encapsulation layer is a single layer, it can be an ion conductor coating layer formed by one ion conductor material, or a mixed ion conductor coating layer formed by a mixture of multiple ion conductor materials. When the ion conductor encapsulation layer is a multilayer, it can be a composite ion conductor layer formed by ion conductor material coating layers formed by different ion conductor materials.

[0090] When the encapsulation layer 20 is only provided with an ion conductor encapsulation layer, it should at least meet the above-mentioned compactness characteristics, that is, at least be able to isolate water vapor or carbon dioxide in the environment to ensure the lithium replenishment stability and processing performance of the positive electrode lithium replenishment additive.

[0091] In the embodiment, the ion conductor encapsulation layer can enhance the ion conductivity of the functional package 20, thereby enhancing the ion conductivity of the positive electrode lithium supplement additive, which is beneficial to the lithium ion transfer of the core 10; at the same time, after the core 10 releases the lithium ions as a "sacrifice", the ion conductor encapsulation layer 22 can also be reused to play an auxiliary role in enhancing ion transmission inside the positive electrode. In another embodiment, the material of the ion conductor encapsulation layer includes at least one of a perovskite type, a NASICON type, a garnet type or a polymer type solid electrolyte. In a specific embodiment, the perovskite type includes Li 3x La 2 / 3-x TiO3 (LLTO), such as Li 0.5 La 0.5 TiO3、Li 0.33 La0.57 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 0.01O3 , Li 0.5 La 0.5 Ti 0.95 Zr 0.05 O3, etc., NASICON type such as but not limited to Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP), garnet type including Li7La3Zr2O 12 LLZO, Li 6.4 Ln3Z 1.4 Ta 0.6 O 12 , Li 6.5 Ln3Z 1.5 Ta 0.5 O 12 At least one of the above, the polymer solid electrolyte includes at least one of PEO / PPO / PVDF etc. which dissolves lithium salt. By adjusting the material of the ion conductor encapsulation layer, its ion conductivity can be further improved.

[0092] In another embodiment, the encapsulation layer 20 may include a composite layer of the electronic conductor encapsulation layer and the ion conductor encapsulation layer. The electronic conductor encapsulation layer may cover the core body 10, and the ion conductor encapsulation layer may cover the outer surface of the electronic conductor encapsulation layer; or the ion conductor encapsulation layer may cover the core body 10, and the electronic conductor encapsulation layer may cover the outer surface of the ion conductor encapsulation layer. In the composite layer, the electronic conductor encapsulation layer and the ion conductor encapsulation layer may not be dense, but the composite layer together should be dense.

[0093] In another embodiment, based on the encapsulation layer 20 structure in the above embodiments, other functional coating layers can be added as needed. As long as it is based on the material of the positive electrode lithium supplement additive core 10 in the above embodiments, any functional modification structure and material made to the encapsulation layer 20 is within the scope disclosed in this specification.

[0094] In a further embodiment, lithium carbonate is dispersed in the encapsulation layer 20 or at the interface between the encapsulation layer 20 and the core 10. The presence of lithium carbonate can improve the compactness of the encapsulation layer 20, improve the lithium replenishment effect and stability of the core 10, and effectively reduce the residual alkali content in the positive electrode lithium replenishment additive, giving the lithium replenishment additive of the present application excellent processing performance.

[0095] In the embodiment, lithium carbonate is mainly distributed at the interface where the encapsulation layer 20 contacts the core 10. This distribution feature of lithium carbonate can effectively reduce the content of residual alkali in the positive electrode lithium supplement additive, and improve the effect of the encapsulation layer 20 covering the core 10 to isolate water vapor and carbon dioxide, thereby improving the lithium supplement stability and lithium supplement effect of the lithium supplement additive.

[0096] In the embodiment, the content of lithium carbonate accounts for 0.5-1.5wt% of the mass of the encapsulation layer 20. In a further embodiment, the content of lithium carbonate is 1-1.5wt%, and specifically can be 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, etc. Typical but non-limiting contents. By controlling the content of lithium carbonate to further reduce the content of residual alkali in the positive electrode lithium supplement additive, especially the content of residual alkali in the encapsulation layer 20, the processing performance of the positive electrode lithium supplement additive in the embodiment of the present application is further improved, while improving the lithium supplement stability and lithium supplement effect of the positive electrode lithium supplement additive in the embodiment of the present application and improving the conductivity of the encapsulation layer 20, stimulating the gram capacity of the lithium supplement additive.

[0097] Based on the structure and performance of the lithium supplement additive in the above text application embodiment, the lithium supplement additive in the above text application has excellent storage and processability and stable electrochemical performance. As detected, the positive electrode sheet directly prepared by the lithium supplement additive in the present application embodiment, such as the positive electrode sheet (not containing positive electrode active material) prepared by the positive electrode lithium supplement additive, binder and conductive agent, is stored for 20 hours at an ambient humidity of 25%. The capacity decay rate relative to the storage of 0.5 hours is not more than 30%, and further not more than 16%, and the capacity stored for 20 hours at an ambient humidity of 10% is not more than 20%, and further not more than 8.5%. Thus, it is reflected that the lithium supplement additive in the present application embodiment has excellent storage and high lithium supplement effect and lithium supplement stability. Ideally, the lithium supplement additive in the above text application is stored in a dry, oxygen-free favorable environment such as a vacuum environment to achieve the maximum performance of the electrochemical performance of the lithium supplement additive in the above text application.

[0098] In a fourth aspect, the present application also provides a method for preparing the positive electrode lithium supplement additive described above. In the embodiment, the process flow of the preparation method of the positive electrode lithium supplement additive is as follows: Figure 3 As shown, combined with Figure 2 , and its preparation method comprises the following steps:

[0099] Step S03: providing core material;

[0100] Step S04: In a protective atmosphere, a packaging layer covering the core material is formed on the surface of the core material to obtain a positive electrode lithium supplement additive.

[0101] Among them, the core material in step S03 is the material contained in the core 10 contained in the positive electrode lithium supplement additive in the above text application embodiment. Therefore, the core material includes a lithium supplement material, and the lithium supplement material is a manganese-based lithium supplement material in the above text application embodiment. The encapsulation layer in step S04 is the encapsulation layer 20 contained in the positive electrode lithium supplement additive in the above text application embodiment. Therefore, in order to save space, the core material in step S03 and the encapsulation layer in step S04 are not described in detail here.

[0102] The encapsulation layer formed in step S04 can be prepared according to the structure of the encapsulation layer 20 contained in the positive electrode lithium supplement additive in the above-mentioned embodiment of the application.

[0103] As shown in the embodiment, the encapsulation layer forming method in step S04 includes the following steps:

[0104] In a protective atmosphere, the precursor of the encapsulation layer is mixed with the core material and then subjected to a second sintering process, wherein the second sintering process contains a first carbon source.

[0105] Among them, the protective atmosphere can be an inert atmosphere, such as an atmosphere formed by any protective gas including nitrogen, argon, nitrogen-argon mixed gas, nitrogen-hydrogen mixed gas, and argon-hydrogen mixed gas. The protective atmosphere can effectively ensure the stability of the core body and the formation of the encapsulation layer to improve the stability of the electrochemical performance of the generated positive electrode lithium supplement additive.

[0106] The temperature of the second sintering treatment can be 650-750 ° C. Through the second sintering treatment, the precursor of the encapsulation layer is fully decomposed to generate an encapsulation layer during the second sintering treatment to form a dense coating layer to coat the surface of the core material. The time of the second sintering treatment should be component-specific and can be adjusted according to the thickness of the encapsulation layer, such as the time can be 1-2 h. When the first carbon source is added during the second sintering treatment, it can react with the raw material residue or other residual alkali contained in the core body during the second sintering process to generate a certain amount of lithium carbonate cracking. In addition, the first carbon source can be a commonly used carbon source, such as but not limited to a solid carbon source or a liquid carbon source.

[0107] In an embodiment, when the encapsulation layer includes an electronic conductor encapsulation layer, and the material of the electronic conductor encapsulation layer is at least one of a carbon material, a conductive polymer or a conductive oxide, the precursor material for forming the electronic conductor encapsulation layer includes a precursor of a carbon material, a conductive polymer or a conductive oxide. Among them, the carbon material, the conductive polymer, and the conductive oxide are all materials of the electronic conductor encapsulation layer contained in the positive electrode lithium supplement additive as described above. Then the precursors of the carbon material, the conductive polymer or the conductive oxide are also precursors for forming the above-mentioned carbon material, the conductive polymer or the conductive oxide, respectively. Then the method and conditions for forming the electronic conductor encapsulation layer of the carbon material, the conductive polymer and the conductive oxide are specifically formed according to the method for forming the carbon material, the conductive polymer or the conductive oxide.

[0108] For example, in a specific embodiment, when the material of the electronic conductor encapsulation layer is a conductive high molecular polymer layer, the method for forming the electronic conductor encapsulation layer may include but is not limited to the following steps:

[0109] The core material is dispersed in a solution containing a conductive high molecular polymer, and then vacuum dried to form an electronic conductor encapsulation layer of the conductive polymer on the surface of the core material. The solvent of the solution is a solvent that can evenly disperse or dissolve the high molecular polymer, such as one or more of N-methylpyrrolidone, methanol, ethanol, isopropanol, acetone, tetrahydrofuran and ether.

[0110] In another specific embodiment, when the material of the electronic conductor encapsulation layer is a carbon material layer, the method for forming the electronic conductor encapsulation layer may include but is not limited to the following steps:

[0111] The core material is dispersed in a solution containing a carbon source, and after drying, a carbonization treatment is performed to form an electronic conductor encapsulation layer of carbon material on the surface of the core material. Among them, the carbon source can be at least one of a solid carbon source and a liquid carbon source. The solid carbon source can be at least one of starch, glucose, fructose, sucrose, cellulose, lignin, amino acids, PEO, epoxy resin, phenolic resin, etc.; the liquid carbon source can be at least one of a liquid alkane, a liquid olefin, and a liquid alkyne with five to sixteen carbons. The temperature of the carbonization treatment can be 400-1000°C, further 400-900°C, and further 450-850°C; the time of the carbonization treatment is 1-12 h, further 1-8 h, and further 1-5 h. In another embodiment, the carbonization treatment can be heated to 400-1000°C at a heating rate of 0.5-10°C / min, further 1-6°C / min, and further 2-5°C / min. For example, when the carbon source is PEO, the core material and PEO can be evenly mixed. PEO reaches its melting point at 300°C and is evenly coated on the surface of the core material. The coated material is sintered in an inert atmosphere at 600°C for 16 hours to form a carbon layer.

[0112] In another embodiment, when the formed encapsulation layer includes an ion conductor encapsulation layer, and when the material of the ion conductor encapsulation layer is at least one of perovskite, NASICON, garnet or polymer solid electrolytes, the precursor material for forming the ion conductor encapsulation layer includes a precursor of a perovskite, NASICON, garnet or polymer solid electrolyte, and the method and conditions for forming the ion conductor encapsulation layer are specifically formed according to the method for forming a perovskite, NASICON, garnet or polymer solid electrolyte.

[0113] In addition, when the material of the encapsulation layer is non-organic, a carbon source is added during the process of forming the encapsulation layer in step S04, so that a certain amount of lithium carbonate is formed in the encapsulation layer, especially at the interface between the core body and the encapsulation layer.

[0114] Or when the material of the encapsulation layer is non-organic, after forming the encapsulation layer in step S04, the following steps are also included:

[0115] In an environment containing a second carbon source, the positive electrode lithium supplement additive with the encapsulation layer formed in step S04 is heat-treated to form a certain content of lithium carbonate in the encapsulation layer, especially at the interface between the core body and the encapsulation layer.

[0116] Wherein. The temperature of the heat treatment can be 400-800 ° C, and the time can be 2-10 h. By adding these carbon source treatments during or after the formation of the encapsulation layer, the residual alkali in the core body 10 is fully reacted, the content of the residual alkali is reduced, and the generated product includes at least lithium carbonate. The lithium carbonate is appropriately controlled, such as the content of lithium carbonate is controlled to account for 0.5-1.5wt% of the mass of the encapsulation layer, so as to reduce the content of the residual alkali of the positive electrode lithium supplement additive and improve the compactness of the encapsulation layer, thereby improving the lithium supplement effect and processing performance of the positive electrode lithium supplement additive. The above-mentioned second carbon source can be a commonly used solid carbon source or liquid carbon source.

[0117] Therefore, the preparation method of the above-mentioned positive electrode lithium supplement additive can effectively prepare the positive electrode lithium supplement additive of the above text application embodiment with a core-shell structure, thereby ensuring that the prepared positive electrode lithium supplement additive has the lithium supplement effect and stable lithium supplement performance and good processing performance described in the above text application embodiment positive electrode lithium supplement additive, and more importantly, it can effectively suppress or reduce the generation of gas during the initial cycle of the battery, and improve the cycle performance and safety performance of the battery. In addition, the relevant performance of the prepared positive electrode lithium supplement additive can be optimized by controlling the materials and process conditions of the core body and the encapsulation layer. Moreover, the preparation method of the positive electrode lithium supplement additive can ensure that the structure and electrochemical performance of the prepared positive electrode lithium supplement additive are stable, and the efficiency is high, saving production costs.

[0118] In the fifth aspect, the embodiment of the present application also provides a positive electrode sheet. The positive electrode sheet of the embodiment of the present application includes a current collector and a positive electrode active layer bonded to the surface of the current collector, and the positive electrode active layer is doped with the manganese-based lithium supplement material or positive electrode lithium supplement additive of the above-mentioned embodiment of the present application. Since the positive electrode sheet of the embodiment of the present application contains the above-mentioned manganese-based lithium supplement material or positive electrode lithium supplement additive of the embodiment of the present application, during the charging and discharging process, the manganese-based lithium supplement material or positive electrode lithium supplement additive contained in the positive electrode sheet plays the role described above, and can be used as a lithium source as a "sacrificial agent" in the first cycle charging process. It is first consumed to supplement the irreversible lithium ions consumed by the negative electrode to form the SEI film, thereby maintaining the abundance of lithium ions in the battery system. At the same time, during the initial cycle, the structure and chemical properties of the positive electrode sheet are stable, which can effectively inhibit or reduce the generation of gas, and improve the cycle performance and safety performance of the battery. Moreover, the residual alkali content of the manganese-based lithium supplement material or the positive electrode lithium supplement additive can be further reduced, which improves the quality of the positive electrode active layer, that is, improves the quality of the positive electrode sheet, thereby improving the first effect of the battery and the overall electrochemical performance.

[0119] In one embodiment, the mass content of the positive electrode lithium replenishing additive in the above-mentioned embodiment of the present application contained in the positive electrode active layer can be 4-10 wt%; preferably, 5~8%. In addition to the above-mentioned positive electrode lithium replenishing additive, the positive electrode active layer also includes a positive electrode active material, a binder and a conductive agent. In the embodiment, the content of the binder in the positive electrode active layer can be 0.5-3wt%. In the embodiment, the binder can be a commonly used positive electrode binder, such as one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivatives.

[0120] In an embodiment, the content of the conductive agent in the positive electrode active layer may be 0.2-5wt%; in an embodiment, the conductive agent may be a commonly used conductive agent, such as one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nanotubes. In an embodiment, the positive electrode active material may include one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, fluorolithium vanadium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide. In an embodiment, the positive electrode sheet preparation process may be: the positive electrode active material, the positive electrode lithium supplement additive, the conductive agent and the binder are mixed to obtain an electrode slurry, the electrode slurry is coated on the current collector, and the positive electrode sheet is prepared through drying, rolling, die cutting and other steps.

[0121] In a sixth aspect, the present application also provides a secondary battery. The secondary battery of the present application includes necessary components such as a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, and of course other necessary or auxiliary components. Among them, the positive electrode sheet is the positive electrode sheet of the present application embodiment described above.

[0122] Since the secondary battery in the embodiment of the present application contains the positive electrode sheet of the embodiment of the above text application, that is, it contains a manganese-based lithium replenishing material or a positive electrode lithium replenishing additive, based on the excellent chemical stability and lithium replenishing effect of the positive electrode lithium replenishing additive in the embodiment of the above text application or further has ion conductivity and / or electronic conductivity, the secondary battery in the embodiment of the present application is endowed with excellent cycle performance and safety performance, and at the same time has excellent first coulomb efficiency and battery capacity, long life, and stable electrochemical performance.

[0123] The following uses a number of specific embodiments to illustrate the manganese-based lithium supplement material, positive electrode lithium supplement additive, and preparation method and application thereof of the embodiments of the present application.

[0124] 1. Manganese-based lithium supplement material, positive electrode lithium supplement additive and preparation method thereof:

[0125] Example A1

[0126] This embodiment provides a manganese-based lithium supplement material and a preparation method thereof. The manganese-based lithium supplement material includes a main phase Li6Mn 1 O4 and combined with Li6Mn in the main phase 1 The secondary phase Mn2O3 on the surface of O4. Among them, the main phase Li6Mn 1 The mass content of O4 in the manganese-based lithium-supplementing material is 90%, and its particle size D50 is 1.5 µm; the mass content of the secondary phase Mn2O3 in the manganese-based lithium-supplementing material is 10%, and its particle size D50 is 0.7 µm.

[0127] The method for preparing a manganese-based lithium supplement material comprises the following steps:

[0128] S1: mixing Li2O and MnO in a molar ratio of 1:1.1 and ball milling to obtain a mixture precursor;

[0129] S2: The obtained mixed precursor is heated to 500° C. and kept warm for 6 hours in an Ar atmosphere doped with oxygen at a volume concentration of 0.3%, and cooled naturally to obtain a manganese-based lithium supplement material including a main phase Li6MnO4 and a secondary phase Mn2O3 bonded to its surface.

[0130] Example A2

[0131] This embodiment provides a manganese-based lithium supplement material, a positive electrode lithium supplement additive and a preparation method thereof. The manganese-based lithium supplement material is the manganese-based lithium supplement material prepared in Example A1, and the positive electrode lithium supplement additive includes a core body of the manganese-based lithium supplement material and a dense carbon coating layer coating the core body, which is denoted as manganese-based lithium supplement material @C, where @ is coating.

[0132] The preparation method of manganese-based lithium supplement material and positive electrode lithium supplement additive comprises the following steps:

[0133] S1: preparing a manganese-based lithium-supplementing material according to the method for preparing a manganese-based lithium-supplementing material in Example A1;

[0134] S2: The manganese-based lithium supplement material prepared in step S1 is crushed, passed through a 200-mesh sieve, mixed with a carbon source, and then heat-treated to complete carbon coating to obtain a positive electrode lithium supplement additive of the manganese-based lithium supplement material @C.

[0135] Example A3

[0136] This embodiment provides a manganese-based lithium supplement material and a preparation method thereof. The manganese-based lithium supplement material includes a main phase Li6Mn 1 O4 and the secondary phase MnO2 bound on its surface. Among them, the main phase Li6Mn 1 The mass content of O4 in the manganese-based lithium-supplementing material is 88%, and its particle size D50 is 1.4 µm; the mass content of the secondary phase MnO2 in the manganese-based lithium-supplementing material is 12%, and its particle size D50 is 0.6 µm.

[0137] The method for preparing a manganese-based lithium supplement material comprises the following steps:

[0138] S1: mixing Li2O and MnO in a molar ratio of 1:1.15 and ball milling to obtain a mixture precursor;

[0139] S2: The obtained mixed precursor is heated to 600° C. and kept warm for 5 hours in an Ar atmosphere doped with oxygen at a volume concentration of 0.5%, and cooled naturally to obtain a manganese-based lithium supplement material including a main phase Li6MnO4 and a secondary phase MnO2 bonded on its surface.

[0140] Example A4

[0141] This embodiment provides a manganese-based lithium supplement material, a positive electrode lithium supplement additive and a preparation method thereof. The manganese-based lithium supplement material is the manganese-based lithium supplement material prepared in Example A3, and the positive electrode lithium supplement additive includes a core of the manganese-based lithium supplement material and a dense carbon coating layer coating the core, which is denoted as manganese-based lithium supplement material @C, where @ is coating.

[0142] The preparation method of manganese-based lithium supplement material and positive electrode lithium supplement additive comprises the following steps:

[0143] S1: preparing a manganese-based lithium-supplementing material according to the method for preparing a manganese-based lithium-supplementing material in Example A3;

[0144] S2: The manganese-based lithium supplement material prepared in step S1 and polyvinyl pyrrolidone (PVP) are mixed in a mass ratio of 95%:5% and crushed, passed through a 200-mesh sieve, mixed with a carbon source and heat-treated to complete carbon coating, thereby obtaining a positive electrode lithium supplement additive of the manganese-based lithium supplement material @C.

[0145] Example A5

[0146] This embodiment provides a manganese-based lithium supplement material and a preparation method thereof. The manganese-based lithium supplement material includes a main phase Li2Mn 1 O2 and combined in the main phase Li2Mn 1 Compared with Example 1, the molar ratio of Li2O and MnO is controlled so that the main phase is Li2Mn 1 O2.

[0147] Comparative Example A1

[0148] This comparative example provides a manganese-based lithium supplement material. Compared with Example 1, the manganese-based lithium supplement material is a single-phase Li6MnO4, that is, it does not contain Mn2O3 or MnO2 secondary phase. The preparation method is as follows:

[0149] S1: mixing Li2O and MnO in a molar ratio of 1:1 and ball milling to obtain a mixture precursor;

[0150] S2: The obtained mixed precursor is heated to 450°C, and kept warm for 8 hours in a high-purity Ar atmosphere, and cooled naturally to obtain Li6MnO4 lithium supplement material, which does not contain Mn2O3 or MnO2.

[0151] Comparative Example A2

[0152] This comparative example provides a manganese-based lithium supplement material. The manganese-based lithium supplement material includes a main phase Li6MnO4 and a secondary phase Mn2O3. The difference from Example 1 is that the main phase Li6MnO4 and the secondary phase Mn2O3 form a physical mixture, that is, the secondary phase Mn2O3 is not bonded to the surface of the main phase Li6MnO4. The preparation method is as follows:

[0153] The Li6MnO4 obtained in Comparative Example 1 and the Mn2O3 purchased from the market were mixed in a ratio of 9:1, ball-milled for 4 hours, and then passed through a 200-mesh sieve.

[0154] 2. Lithium-ion battery example:

[0155] The lithium supplement materials provided in the above-mentioned Examples A1 to A5 and the lithium supplement materials provided in the comparative examples are respectively assembled into positive electrodes and lithium ion batteries according to the following methods:

[0156] Positive electrode: The lithium supplement materials provided in the above-mentioned Examples A1 to A5 and Comparative Examples A1 to A2 are mixed with lithium supplement materials and lithium cobalt oxide at a mass ratio of 5:95 to obtain a mixture, and the mixture is mixed with polyvinylidene fluoride and SP-Li at a mass ratio of 95:3:2 by ball milling and stirring to obtain a positive electrode slurry, and the positive electrode slurry is coated on the surface of aluminum foil, rolled, and vacuum dried at 110° C. overnight to obtain each positive electrode sheet; at the same time, the state of the positive electrode slurry in each example is observed and recorded, and the observation and recording results are shown in Table 1 below;

[0157] Negative electrode: lithium metal sheet;

[0158] Electrolyte: Ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7, and LiPF6 was added to form an electrolyte, and the concentration of LiPF6 was 1 mol / L.

[0159] Diaphragm: Polypropylene microporous separator;

[0160] Lithium-ion battery assembly: Lithium-ion batteries are assembled in an inert atmosphere glove box in the order of lithium metal sheet-diaphragm-electrolyte-positive electrode sheet.

[0161] 3. Related feature tests

[0162] 1. Characterization of manganese-based lithium supplement materials and positive electrode lithium supplement additives:

[0163] The manganese-based lithium supplement materials in Examples A1 to A5 and Comparative Example A1 were subjected to X-ray diffraction (XRD) analysis. 1 O4(Li2Mn 1 O2·2Li2O) XRD diagram. The manganese-based lithium supplement materials provided in other embodiments A2 to A5 also show corresponding main phase and secondary phase characteristic peaks. From XRD, it can be seen that after comparison with the PDF card, the manganese-based lithium supplement material provided in the embodiment of the present application is mainly composed of Li2Mn 1 O2·xLi2O, specifically Li6MnO4 (Li2Mn 1 O2·2Li2O)、Li2Mn 1 O2 and Mn2O3, among which Li2Mn 1 O2 such as Li6MnO4 is the main phase, containing a small amount of Mn2O3 or MnO2. In comparative example A1, there are no characteristic peaks of Mn2O3 and MnO2.

[0164] 2. Moisture resistance test of positive electrode lithium supplement additives:

[0165] In order to further evaluate the moisture resistance of the above lithium supplement material, we separately mixed the lithium supplement material, the conductive agent and the binder to prepare the pole piece (without adding the positive electrode material), and the specific steps are as follows: the lithium supplement material in the embodiment or comparative example is mixed with SP and PVDF in a mass ratio of 80:8:12 and stirred by ball milling for 60 minutes; the rest of the steps are the same as above. Except for the positive electrode piece, the rest of the battery components are the same as above and remain unchanged.

[0166] Here, we take Example 2 as an example and test the specific capacity of the corresponding electrode sheet at different humidity (25%, 20%, 10%) for different storage time, and the relevant results are shown in Tables 2, 3, and 4. It can be seen from Tables 1-3 that the specific capacity of the positive electrode sheet prepared by the positive electrode lithium supplement additive in Example 2 of the present application changes when the battery is stored at different humidity, but the change is not large, especially when the humidity is 10%, the specific capacity after 20 hours of storage is relatively small relative to the specific capacity after 0.5 hours of storage, that is, the attenuation rate is only 8.5% (Note: Attenuation rate = (1-specific capacity after 20 hours of storage / specific capacity after 0.5 hours of storage) * 100%.

[0167] Table 1

[0168]

[0169] Table 2

[0170]

[0171] Table 3

[0172]

[0173] 3. Electrochemical performance of lithium-ion batteries:

[0174] The performance of the lithium-ion batteries treated with lithium supplementation in Examples A1 to A5 and Comparative Examples A1-A2 was tested according to the following methods:

[0175] The button cell was charged to 4.3 V at a constant current and constant voltage of 0.05 C, with a cut-off current of 0.01 C. After standing for 5 min, the cell was discharged to 3.0 V at a rate of 0.05 C.

[0176] The relevant electrochemical performance test results of lithium-ion batteries are shown in Table 4 below.

[0177] Table 4

[0178]

[0179] As shown in Table 4, the first efficiency of the battery containing the manganese-based lithium supplement material of the present application embodiment is lower than that of the comparative battery, and its gram capacity is significantly improved compared with the comparative battery (from 5-6 mAh / g to more than 10 mAh / g). 1 O2·xLi2O and Mn a 2 O b The synergistic effect between the two phases improves the lithium replenishment effect, and its high chemical stability improves the cycle performance and safety performance of the battery.

[0180] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A manganese-based lithium supplement material, characterized in that: At least Li2Mn as the main phase 1 O2·xLi2O and Mn as a secondary phase a 2 O b , and the Mn a 2 O b It is combined with Li2Mn 1 The surface of O2·xLi2O, where 0≤x≤2, the Mn a 2 O b a is 1-2, b is 2-3; the secondary phase Mn a 2 O b The particle size of the main phase Li2Mn 1 The particle size of O2·xLi2O is small; The Mn a 2 O b The mass content M2 in the manganese-based lithium supplement material is 0<M2≤12%.

2. The manganese-based lithium supplement material according to claim 1, characterized in that: The Li2Mn 1 The mass content M1 of O2·xLi2O in the manganese-based lithium supplement material is 88%≤M1<100%; and / or The Li2Mn 1 The particle size D50 of O2·xLi2O is 1-3 µm; and / or The Mn a 2 O b has a particle size D50 of 0.2-1.3 µm; and / or The Mn a 2 O b Includes at least one of Mn2O3 and MnO2.

3. The manganese-based lithium supplement material according to claim 1 or 2, characterized in that: The first lithium removal capacity of the manganese-based lithium supplement material is above 400 mAh / g.

4. A method for preparing a manganese-based lithium supplement material, characterized in that: The steps include: Mixing a manganese source and a lithium source to obtain a mixture precursor; The mixture precursor is subjected to a first sintering treatment in an oxygen-containing atmosphere to generate at least Li2Mn 1 O2·xLi2O and Mn as a secondary phase a 2 O b , and the Mn a 2 O b It is combined with Li2Mn 1 O2·xLi2O surface, and the secondary phase Mn a 2 O b The particle size of the main phase Li2Mn 1 The particle size of O2·xLi2O is small; wherein the Mn a 2 O b Where a is 1-2, b is 2-3, and a manganese-based lithium supplement material is obtained; the Mn a 2 O b The mass content M2 in the manganese-based lithium supplement material is 0<M2≤12%.

5. The preparation method according to claim 4, characterized in that: The temperature of the first sintering treatment is 400-600° C. and the time is 4-8 hours; and / or The oxygen-containing atmosphere is an atmosphere composed of a mixture of a chemically inert gas and oxygen, and the volume concentration of oxygen in the mixture is 0.1%-1%; The manganese source and the lithium source are mixed in a ratio of manganese to lithium of 1:2 to 1:2.4; The manganese source comprises MnO; and / or The lithium source includes at least one of lithium oxide and LiOH.

6. A positive electrode lithium supplement additive, comprising a core body and an encapsulation layer covering the core body, characterized in that: The core body includes a lithium-supplementing material, and the lithium-supplementing material is the manganese-based lithium-supplementing material according to any one of claims 1 to 3 or the manganese-based lithium-supplementing material prepared by the preparation method according to any one of claims 4 to 5.

7. The positive electrode lithium supplement additive according to claim 6, characterized in that: The thickness of the encapsulation layer is 2-10 nm; The mass of the encapsulation layer accounts for 1%-5% of the total mass of the positive electrode lithium supplement additive; and / or The encapsulation layer comprises at least one of an ion conductor encapsulation layer and an electron conductor encapsulation layer; and / or Lithium carbonate is dispersed in the encapsulation layer or at the interface between the encapsulation layer and the core body.

8. The positive electrode lithium supplement additive according to any one of claims 6 to 7, characterized in that: The capacity decay rate of the positive electrode sheet prepared by the positive electrode lithium supplement additive, the conductive agent and the binder stored for 20 hours under an ambient humidity of 25% relative to that stored for 0.5 hours is not greater than 30%; and / or The capacity attenuation rate of the positive electrode sheet prepared by the positive electrode lithium supplement additive, the conductive agent and the binder stored for 20 hours under an ambient humidity of 10% relative to that stored for 0.5 hours is no more than 20%.

9. A method for preparing a positive electrode lithium supplement additive, comprising the following steps: Providing a core material, wherein the core material comprises the manganese-based lithium-supplementing material according to any one of claims 1 to 3 or the manganese-based lithium-supplementing material prepared by the preparation method according to any one of claims 4 to 5; In a protective atmosphere, a packaging layer covering the core material is formed on the surface of the core material to obtain a positive electrode lithium supplement additive.

10. The preparation method according to claim 9, characterized in that: The method for forming an encapsulation layer covering the core material on the surface of the core material comprises the following steps: In the protective atmosphere, a precursor of the encapsulation layer is mixed with the core material and then subjected to a second sintering process, wherein the second sintering process contains a first carbon source; or After the step of forming a packaging layer covering the core material on the surface of the core material, the step further includes heat treating the generated positive electrode lithium supplement additive in an environment containing a second carbon source.

11. A positive electrode sheet, comprising a current collector and a positive electrode active layer bonded to the surface of the current collector, characterized in that: The positive electrode active layer is doped with the manganese-based lithium replenishing material according to any one of claims 1 to 3 or the manganese-based lithium replenishing material prepared by the preparation method according to any one of claims 4 to 5 or the positive electrode lithium replenishing additive according to any one of claims 6 to 8 or the positive electrode lithium replenishing additive prepared by the preparation method according to any one of claims 9 to 10.

12. A secondary battery, comprising a positive electrode sheet and a negative electrode sheet, characterized in that: The positive electrode sheet is the positive electrode sheet according to claim 11.

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