Lithium supplementing additive, preparation method and application thereof

Abstract

The application provides a lithium supplement additive and a preparation method and application thereof. The lithium supplement additive comprises a lithium-rich material, and the lithium-rich material is a lithium-rich oxide. The particle structure of the lithium-rich material comprises a central region and a surface layer region arranged in sequence from inside to outside. The surface layer region contains first oxygen vacancies, and the concentration of the first oxygen vacancies gradually decreases from the side close to the central region to the side far from the central region. The lithium supplement additive provided by the application comprises a lithium-rich material, and the lithium-rich material comprises a central region and a surface layer region. In the surface layer region, the concentration of oxygen vacancies gradually decreases from inside to outside. The arrangement can effectively reduce the diffusion of surface oxygen vacancies to the inside and the structural instability and continuous oxygen and gas production caused thereby, and can also reduce the occurrence of electrolyte side reactions, thereby reducing gas production.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a lithium supplementation additive, its preparation method and application. Background Technology

[0002] During the initial charge and discharge process of lithium-ion batteries, a large amount of solid electrolyte interface film forms on the surface of the negative electrode, consuming the limited lithium ions and electrolyte in the battery, causing irreversible capacity loss, reducing the energy density of lithium-ion rechargeable batteries, and decreasing the charge and discharge efficiency of electrode materials, thus limiting the application of lithium-ion batteries. In existing technologies, adding lithium-replenishing materials to the positive electrode can effectively compensate for the initial irreversible capacity loss of lithium batteries. However, research and practical applications have revealed that existing lithium-replenishing additives, due to decomposition reactions and the promotion of electrolyte decomposition, can lead to increased gas production during the formation stage of lithium-ion batteries. This can cause gas expansion within the sealed battery system, resulting in battery volume expansion and safety issues. Therefore, there is an urgent need to develop positive electrode lithium-replenishing additives with low gas production and good lithium-replenishing effects. Summary of the Invention

[0003] In view of this, one object of this application is to provide a lithium supplement additive, which includes a lithium-rich material comprising a central region and a surface region, wherein the oxygen vacancy concentration in the surface region gradually decreases from the inside to the outside. This configuration can effectively reduce the diffusion of surface oxygen vacancy into the interior and the resulting structural instability and continuous oxygen and gas production, and can also reduce the occurrence of electrolyte side reactions, thereby reducing gas production.

[0004] Another objective of this application is to provide a method for preparing a lithium supplement additive.

[0005] Another objective of this application is to provide a lithium-rich cathode.

[0006] Another object of this application is to provide a secondary battery.

[0007] To achieve the above objectives, a first aspect of this application provides a lithium supplementation additive, comprising a lithium-rich material, wherein the lithium-rich material is a lithium-rich oxide; the particle structure of the lithium-rich material comprises a central region and a surface region arranged sequentially from the inside out, the surface region containing a first oxygen vacancy, and the concentration of the first oxygen vacancy gradually decreases from the side closer to the central region to the side farther away from the central region.

[0008] In some embodiments of this application, the first oxygen vacancy accounts for 0.5-10.0 at% of all oxygen atoms in the lithium-rich oxide.

[0009] In some embodiments of this application, the average radius of the central region is 3 / 5 to 2 / 5 of the average radius of the lithium-rich material particles, and the thickness of the surface region is 2 / 5 to 3 / 5 of the average radius of the lithium-rich material particles.

[0010] In some embodiments of this application, the median particle size of the lithium-rich material particles is between 1 and 30 μm, and the average radius of the lithium-rich material particles is between 0.5 and 15 μm.

[0011] In some embodiments of this application, the surface region includes at least two sub-surface regions with different first oxygen vacancy concentrations; wherein the sub-surface region with a higher first oxygen vacancy concentration among the at least two sub-surface regions is located closer to the central region, and the sub-surface region with a lower first oxygen vacancy concentration among the at least two sub-surface regions is located further away from the central region; the concentration of the first oxygen vacancy in the sub-surface region farthest from the central region is 0-1.0 at.

[0012] In some embodiments of this application, the central region has a second oxygen vacancy; the second oxygen vacancy accounts for 0-5 at% of all oxygen atoms in the lithium-rich oxide.

[0013] In some embodiments of this application, the lithium-rich oxide comprises lithium with the molecular formula Li x M y T z O q The material and / or the molecular formula is Li w The material of O; wherein M includes at least one of Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti and Mg, and T includes at least one of Fe, Co, Mn, Ni, Si and Al, and 0 < x ≤ 6, 0 < y ≤ 1, 0 ≤ z ≤ 2, 0 < q ≤ 5, 1 ≤ w ≤ 2.

[0014] In some embodiments of this application, the lithium supplementation additive further includes a coating layer disposed on the surface of the surface region on the side away from the central region.

[0015] To achieve the above objectives, a second aspect of this application provides a method for preparing a lithium supplementation additive, comprising:

[0016] The lithium source, M source, and T source are mixed in a certain proportion to obtain a mixture;

[0017] The mixture was subjected to a first heat treatment under a protective atmosphere to obtain an intermediate product;

[0018] The intermediate product is subjected to a second heat treatment in an oxygen-rich atmosphere to obtain the lithium-rich material.

[0019] in:

[0020] The M element in the M source includes at least one of Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti, and Mg; and the T element in the T source includes at least one of Fe, Co, Mn, Ni, Si, and Al.

[0021] In some embodiments of this application, the temperature of the first heat treatment is 500-900°C, and the duration of the first heat treatment is 6-48 hours.

[0022] In some embodiments of this application, the protective atmosphere is one of vacuum, inert gas, or hydrogen atmosphere.

[0023] In some embodiments of this application, the oxygen-enriched atmosphere is pure oxygen or a mixture of oxygen and an inert gas; when the oxygen-enriched atmosphere is a mixture of oxygen and an inert gas, the volume percentage of oxygen in the oxygen-enriched atmosphere is between 50% and 100%.

[0024] In some embodiments of this application, when the oxygen-enriched atmosphere is a mixture of oxygen and inert gas, the initial oxygen volume percentage in the oxygen-enriched atmosphere is j%, and then the oxygen volume percentage gradually increases at k% / min, where 50≦j<100, 0<k≤2.

[0025] In some embodiments of this application, the temperature of the second heat treatment is 200-500°C, and the time of the second heat treatment is 1-10 hours.

[0026] In some embodiments of this application, the method for preparing the lithium-rich additive further includes forming a coating layer on the surface of the lithium-rich material.

[0027] To achieve the above objectives, a third aspect of this application provides a lithium-rich cathode, which includes a cathode active material and a lithium-replenishing additive prepared by the method of the lithium-replenishing additive preparation method of the embodiments of this application or the embodiments of this invention.

[0028] To achieve the above objectives, a fourth aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, and a separator, wherein the positive electrode is a lithium-rich positive electrode according to the embodiments of this application.

[0029] The lithium supplement additive of this application embodiment can bring the following beneficial effects:

[0030] 1. The lithium-rich additive in this application includes a lithium-rich material, which comprises a central region and a surface region. In the surface region, the oxygen vacancy concentration gradually decreases from the inside to the outside. This configuration can effectively reduce the diffusion of surface oxygen vacancy into the interior and the resulting structural instability and continuous oxygen and gas production.

[0031] 2. Oxygen vacancy sites have high reactivity and can easily cause side reactions in the electrolyte, resulting in gas production. Therefore, the lithium supplementation additive in this application reduces the occurrence of side reactions in the electrolyte by reducing the oxygen vacancy sites on the surface of the lithium supplementation additive, thereby reducing gas production.

[0032] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0033] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0034] Figure 1 This is a simplified structural diagram of a lithium supplement additive according to an embodiment of this application (no oxygen vacancies in the central region, no sub-surface layer in the surface region, and no coating layer).

[0035] Figure 2 This is a simplified structural diagram of a lithium supplement additive according to another embodiment of this application (the central region has oxygen vacancies, the surface region has no sub-surface layer, and no coating layer)).

[0036] Figure 3 This is a simplified structural diagram of a lithium supplement additive according to another embodiment of this application (no oxygen vacancies in the central region, no sub-surface layer in the surface region, and a coating layer).

[0037] Figure 4 This is a simplified structural diagram of a lithium supplement additive according to another embodiment of this application (no oxygen vacancies in the central region, four sub-layers in the surface region, and no coating layer).

[0038] Figure 5 This is a simplified structural diagram of a lithium supplement additive according to another embodiment of this application (no oxygen vacancies in the central region, three sub-layers in the surface region, and no coating layer).

[0039] Figure 6 This is a simplified structural diagram of a lithium supplement additive according to another embodiment of this application (the central region has oxygen vacancies, the surface region has 3 sub-surface layers, and there is a coating layer).

[0040] Figure label:

[0041] 1-Central region; 2-Surface region; 201-Sub-surface region; 202-First sub-surface region; 203-Second sub-surface region; 204-Third sub-surface region; 3-First oxygen vacancy; 4-Second oxygen vacancy; 5-Covering layer. Detailed Implementation

[0042] The embodiments of this application are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0043] In this document, the disclosure of numerical ranges includes all values ​​across the entire range and the disclosure of further subdivisions of the ranges, including the endpoints and subranges given for these ranges.

[0044] Unless otherwise specified, all raw materials and equipment mentioned in this article are those that can be manufactured commercially or by known methods; and all methods mentioned are conventional methods unless otherwise specified.

[0045] A lithium supplement additive according to an embodiment of this application is described below with reference to the accompanying drawings.

[0046] like Figure 1 As shown, the lithium supplement additive of this application includes a lithium-rich material, which is a lithium-rich oxide; the particle structure of the lithium-rich material includes a central region 1 and a surface region 2 arranged sequentially from the inside to the outside, the surface region 2 contains a first oxygen vacancy 3, and the concentration of the first oxygen vacancy 3 gradually decreases from the side closer to the central region 1 to the side farther away from the central region 1.

[0047] The lithium supplement additive of this application includes a lithium-rich material, which comprises a central region and a surface region. In the surface region, the oxygen vacancy concentration gradually decreases from the inside to the outside. This setting can effectively reduce the diffusion of surface oxygen vacancy into the interior and the resulting structural instability and continuous oxygen and gas production. It can also reduce the occurrence of electrolyte side reactions, thereby reducing gas production.

[0048] In some implementations, lithium-rich oxides include, but are not limited to, those with the molecular formula Li. x M y T z O q The material, with the molecular formula Li wO is a material selected from at least one of the following: M includes at least one element selected from Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti, and Mg; T includes at least one element selected from Fe, Co, Mn, Ni, Si, and Al; and 0 < x ≤ 6, 0 < y ≤ 1, 0 ≤ z ≤ 2, 0 < q ≤ 5, and 1 ≤ w ≤ 2. As a non-limiting example, x can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3. 7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, or 5.9; y is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9; z is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8. 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9; q is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2 0.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, or 4.9; w is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9. As a possible example, for a molecular formula of Li... x M y T z O q The material has the following properties: 1.2 < x ≤ 5, 0.6 < y ≤ 1, 0.2 < z ≤ 2, 4 < q ≤ 5.

[0049] For the molecular formula Li x M y T z O qIn lithium-rich oxide materials, lithium can effectively compensate for lithium loss during the first charge of a secondary battery. In some implementations, when M is Ni, nickel can enhance the structural framework of the lithium-rich oxide and improve its structural stability. However, nickel has a certain degree of reactivity and is prone to side reactions with the electrolyte, reducing battery performance. Furthermore, the addition of nickel can cause the lithium-replenishing additive to react with water or carbon dioxide to generate residual alkalis such as lithium carbonate or lithium hydroxide. These residual alkalis can firstly cause the electrode slurry to easily form a jelly-like consistency during preparation, which is not conducive to slurry coating; secondly, the residual alkalis can cause the positive electrode sheet to... Side reactions in the electrolyte lead to decomposition and gas production. Furthermore, these residual alkalis can react with the battery current collector at high temperatures, releasing hydrogen gas, causing battery expansion and damage to the current collector, thus reducing battery safety. To improve the stability of lithium-rich additives and suppress the formation of residual alkalis, when M is Ni, T can be at least one of Fe, Co, and Al. At least one of Fe, Co, and Al can enhance the crystal structure strength of lithium-rich materials and reduce the reactivity of lithium and nickel with water or CO2, thereby reducing the content of residual alkalis and improving battery safety and cycle performance. In some embodiments, when M is Ni, T can be Al. Al can effectively reduce the activity of nickel and suppress residual alkali precipitation, which is beneficial for improving the structural stability of lithium-rich additives.

[0050] It should be noted that in this application, oxygen atoms (or oxygen ions) in the crystal lattice detach, resulting in oxygen deficiency and the formation of oxygen vacancies. However, in some cases, oxygen vacancies are not only distributed on the surface of lithium-rich oxides; they may also exist within the oxide itself. It's just that the surface is more susceptible to external environmental influences, making it easier for oxygen vacancies to form. Therefore, in some embodiments, such as... Figure 2 As shown, central region 1 also has oxygen vacancies. For ease of distinction, the oxygen vacancies in the central region are defined as the second oxygen vacancies.

[0051] In this application, the distribution of the second oxygen vacancy is divided into two possible scenarios: In some embodiments, the concentration of the second oxygen vacancy gradually decreases from the inside out (i.e., from the center of the surface region outwards to the position near the surface region), and the concentration of the second oxygen vacancy at the position immediately adjacent to the surface region 2 is greater than the concentration of the first oxygen vacancy at the position immediately adjacent to the central region 1. This ensures that the oxygen vacancy content of the entire lithium-rich material particle has a gradient distribution from the inside out, and the oxygen vacancy concentration gradually decreases along the direction gradually away from the center of the central region. This can effectively reduce the diffusion of surface oxygen vacancy into the interior and the resulting structural instability and continuous oxygen and gas production. At the same time, by reducing the oxygen vacancy on the surface of the lithium-filling additive, the occurrence of electrolyte side reactions can be reduced, thereby reducing gas production. In other embodiments, the concentration of the second oxygen vacancy is irregular, but the overall content is less than the content of the first oxygen vacancy in the surface region. At the same time, the concentration of the second oxygen vacancy immediately adjacent to the surface region may be greater than, equal to, or less than the concentration of the first oxygen vacancy on the side of the surface region immediately adjacent to the central region.

[0052] In some embodiments, the first oxygen vacancy 3 accounts for 0.5-10.0 at% of all oxygen atoms in the lithium-rich oxide. As a non-limiting example, the first oxygen vacancy 3 accounts for 1 at%, 1.5 at%, 2 at%, 2.5 at%, 3 at%, 3.5 at%, 4 at%, 4.5 at%, 5 at%, 5.5 at%, 6 at%, 6.5 at%, 7 at%, 7.5 at%, 8.5 at%, 9 at%, or 9.5 at% of all oxygen atoms in the lithium-rich oxide. As a possible example, the first oxygen vacancy 3 accounts for 3-7 at% of all oxygen atoms in the lithium-rich oxide. When the percentage of the first oxygen vacancy in all oxygen atoms of the lithium-rich oxide is within the above-mentioned range, it is easy to form a distribution pattern of the first oxygen vacancy concentration in the surface region that gradually decreases from the side closer to the central region to the side farther away from the central region, and it can also ensure the structural stability of the lithium supplementation material. If it is less than 0.5 at%, the first oxygen vacancy concentration in the surface region is not likely to form a distribution pattern of gradually decreasing from the side closer to the central region to the side farther away from the central region. If it is greater than 10.0 at%, it will increase the material defects of the lithium supplementation additive. For example, the valence state of some metal elements in the center of the lithium-rich oxide is easy to change, which will lead to material instability and some side reactions at the interface.

[0053] In some embodiments, the second oxygen vacancy 4 accounts for 0-5 at% of all oxygen atoms in the lithium-rich oxide. As a non-limiting example, the second oxygen vacancy 4 accounts for 0 at%, 1 at%, 2 at%, 3 at%, 4 at%, or 5 at% of all oxygen atoms in the lithium-rich oxide. As a possible example, the second oxygen vacancy 4 accounts for 1-4 at% of all oxygen atoms in the lithium-rich oxide. A percentage of the second oxygen vacancy within the above range ensures the structural stability of the lithium-supplementing material; a percentage greater than 5 at% increases material defects in the lithium-supplementing additive.

[0054] In some embodiments, the median particle size D50 of the lithium-rich material particles is between 1 and 30 μm. By way of non-limiting example, the median particle size of the lithium-rich material particles includes, but is not limited to, 3 μm, 6 μm, 9 μm, 12 μm, 15 μm, 18 μm, 21 μm, 24 μm, or 27 μm. Controlling the median particle size of the lithium-rich material particles within the above range is beneficial for lithium-replenishing additives to achieve rapid and effective lithium replenishment of secondary batteries.

[0055] In some embodiments, the average radius of the lithium-rich material particles is between 0.5 and 15 μm. By way of non-limiting example, the average radius of the lithium-rich material particles includes, but is not limited to, 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, or 14 μm. Lithium-rich materials with the above-mentioned average radii, when used as electrode materials, exhibit good particle packing, ensuring effective lithium ion insertion and extraction, thereby guaranteeing the performance of the secondary battery.

[0056] In some embodiments, the average radius of the central region 1 is 3 / 5 to 2 / 5 of the average radius of the lithium-rich material particles, and the thickness of the surface region 2 is 2 / 5 to 3 / 5 of the average radius of the lithium-rich material particles. As a non-limiting example, the average radius of the central region 1 includes, but is not limited to, 42%, 45%, 48%, 51%, 54%, 57%, or 60% of the average radius of the lithium-rich material particles; correspondingly, the thickness of the surface region 2 includes, but is not limited to, 40%, 43%, 46%, 49%, 55%, or 58% of the average radius of the lithium-rich material particles. It is understood that if the thickness of the surface region is less than 2 / 5 of the average radius of the lithium-rich material particles, it is difficult to form a gradient structure of the concentration of the first oxygen vacancy that gradually decreases from the side closer to the central region to the side farther from the central region; if the thickness of the surface region is greater than 3 / 5 of the average radius of the lithium-rich material particles, it will increase the total amount of the first oxygen vacancy in the surface region, which is detrimental to the overall stability of the lithium-rich material structure. Therefore, by setting the thickness of the surface region within the above range, the distribution pattern of the first oxygen vacancy in the surface region of the lithium-rich material can be better controlled to exhibit a gradient decrease, and the total content of the first oxygen vacancy in the surface region can be kept low, thereby ensuring the overall structural stability of the lithium-rich material.

[0057] In some implementation schemes, such as Figure 4 As shown, the surface region 2 includes at least two sub-surface regions 201 with different concentrations of first oxygen vacancies 3. The sub-surface region 201 with a higher concentration of first oxygen vacancies 3 is located closer to the central region 1, while the sub-surface region 201 with a lower concentration of first oxygen vacancies 3 is located further away from the central region 1. That is, it can be stated that, from the side closer to the central region to the side farther from the central region, the surface region includes n sub-surface regions with different oxygen vacancies concentrations, where n is a positive integer greater than or equal to 2, and the oxygen vacancies concentration of the nth sub-surface region is less than that of the (n-1)th sub-surface region. As a non-limiting example, n can be 2, 3, 4, 5, 6, 7, 8, 9, or 10. When the surface region contains multiple sub-surface regions, the concentration of first oxygen vacancies decreases layer by layer from the side closer to the central region to the side farther from the central region, and the specific distribution of first oxygen vacancies within each sub-surface region is not limited. When the number of sub-surface regions reaches a certain level, and the total thickness of the surface region is constant, the thickness of each sub-surface region approaches a point value, and the concentration of the first oxygen vacancy in each sub-surface region also approaches a point value. The concentration of the first oxygen vacancy gradually decreases linearly from the side closer to the center region to the side farther away from the center region throughout the entire surface region.

[0058] In some implementations, the first oxygen vacancy 3 in the nth sub-surface region (i.e., the sub-surface region furthest from the central region) accounts for 0-1 at% of all oxygen atoms in the lithium-rich oxide. As a non-limiting example, the first oxygen vacancy in the nth sub-surface region accounts for 0%, 0.3 at%, 0.6 at%, 0.9 at%, or 1 at% of all oxygen atoms in the lithium-rich oxide. When the first oxygen vacancy content in the nth sub-surface region is within the above range, it facilitates the formation of a gradient distribution of first oxygen vacancy concentration that gradually decreases from the side closer to the central region to the side farther from the central region, ensuring material stability, reducing electrolyte side reactions, and thus reducing gas production. If the first oxygen vacancy content is greater than 1 at%, to ensure that the overall first oxygen vacancy concentration in the surface region gradually decreases from the side closer to the central region to the side farther from the central region, the overall first oxygen vacancy concentration of the lithium-rich oxide particles will be very high, leading to instability in the entire material structure and an increase in side reactions.

[0059] In some implementations, the absolute value of the difference between the first oxygen vacancy concentration in the nth sub-surface region and the first oxygen vacancy concentration in the (n-1)th sub-surface region is |1 / [n(n-1)]-20 / [n(n-1)]|at%. As a non-limiting example, when n = 2-10, the absolute values ​​of the difference between the first oxygen vacancy concentration in the nth sub-surface region and the first oxygen vacancy concentration in the (n-1)th sub-surface region are 9.50at%, 3.16at%, 1.58at%, 0.95at%, 0.63at%, 0.45at%, 0.34at%, 0.26at%, and 0.21at%. The difference between the first oxygen vacancy concentration in the nth sub-surface region and the first oxygen vacancy concentration in the (n-1)th sub-surface region is selected within the above range. On the one hand, it is easy to form a distribution pattern in which the first oxygen vacancy concentration in the surface region gradually decreases from the side closer to the central region to the side farther away from the central region. On the other hand, it can ensure the structural stability of the lithium supplementation material. If it is less than |1 / [n(n-1)]-20 / [n(n-1)]| / n at%, the first oxygen vacancy concentration in the surface region is unlikely to form a distribution pattern in which it gradually decreases from the side closer to the central region to the side farther away from the central region. If it is greater than |1 / [n(n-1)]-20 / [n(n-1)]|at%, it will increase the overall material defects of the lithium supplementation additive. For example, the valence state of some metal elements in the center of the lithium-rich oxide is easy to change, which will lead to material instability and some side reactions at the interface.

[0060] In some implementations, the thickness of each sub-surface region 201 is between 1 / 25 and 3 / 10 of the average radius of the lithium-rich material particles. As a non-limiting example, the thickness of each sub-surface region 201 includes, but is not limited to, 1 / 25, 4 / 25, 1 / 10, 2 / 10, or 3 / 10 of the average radius of the lithium-rich material particles. Setting the thickness of each sub-surface region within the above range ensures, on the one hand, that the lithium-rich material particles have a certain first oxygen vacancy concentration gradient distribution, effectively reducing the diffusion of surface oxygen vacancies into the interior and the resulting structural instability and continuous oxygen and gas production; on the other hand, it does not affect the kinetic transport of ions and electrons, thereby achieving effective lithium replenishment of the battery and ensuring effective lithium ion insertion / extraction, thus guaranteeing the performance of the secondary battery.

[0061] It should be noted that in this application, the thickness of each sub-surface region 201 can be the same or different. However, when the thickness of each sub-surface region 201 is the same, it is easier to compare the gradual trend of the first oxygen vacancy concentration in each sub-surface region.

[0062] As a possible example, such as Figure 5 As shown, the surface region 2 includes a first sub-surface region 202, a second sub-surface region 203, and a third sub-surface region 204, arranged sequentially from the side closest to the central region 1 to the side furthest from the central region 1; the first sub-surface region 202, the second sub-surface region 203, and the third sub-surface region 204 have equal thicknesses. The first oxygen vacancy in the first sub-surface region 202 accounts for 0.2-3.0 at% of all oxygen atoms in the lithium-rich oxide, for example, non-limiting examples could be 0.5 at%, 0.8 at%, 1.1 at%, 1.4 at%, 1.7 at%, 2.1 at%, 2.4 at%, or 2.7 at%. The first oxygen vacancy in the second sub-surface region 203 accounts for 0.1-2.0 at% of all oxygen atoms in the lithium-rich oxide, for example, non-limiting examples could be 0.3 at%, 0.6 at%, 0.9 at%, 1.1 at%, 1.4 at%, or 1.7 at%. The first oxygen vacancy in the third subsurface region 204 accounts for 0-1.0 at% of all oxygen atoms in the lithium-rich oxide, for example, by way of non-limiting enumeration, it could be 0, 0.3 at%, 0.6 at%, or 0.9 at%, etc.

[0063] In some implementation schemes, in order to protect conductivity, such as Figure 3 and Figure 6As shown, the lithium replenishment additive of this application also includes a surface coating layer disposed on the side of the surface region 2 away from the central region 1. Here, the coating layer can be understood as a conductive encapsulation layer. In some embodiments, the coating layer includes, but is not limited to, a carbon layer. The carbon layer material includes, but is not limited to, one or more of graphite, graphene, carbon nanotubes, carbon fibers, acetylene black, soft carbon, hard carbon, or amorphous carbon. The coating layer serves two purposes: firstly, it provides protection, preventing direct contact between lithium-rich oxides and air, reducing capacity loss caused by the reaction of lithium-rich oxides with water or CO2, lowering the residual alkali content of the lithium replenishment additive, facilitating the preparation of the positive electrode slurry, and achieving effective lithium replenishment for lithium secondary batteries; secondly, it provides conductivity, improving the conductivity of the lithium replenishment material, which is beneficial for electron and ion transport.

[0064] The method for preparing the lithium supplement additive according to the embodiments of this application includes the following steps:

[0065] S100: Mix the lithium source, M source and T source according to the specified ratio to obtain a mixture.

[0066] Lithium-rich oxides are those mentioned above, including but not limited to those with the molecular formula Li. x M y T z O q The material, with the molecular formula Li w O is a material containing at least one of the following elements: M includes at least one of the elements Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti, and Mg; T includes at least one of the elements Fe, Co, Mn, Ni, Si, and Al; and 0 < x ≤ 6, 0 < y ≤ 1, 0 ≤ z ≤ 2, 0 < q ≤ 5, and 1 ≤ w ≤ 2.

[0067] In some implementations, the lithium source includes, but is not limited to, one or more of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and lithium oxide. The metal elements in the M and T sources, excluding silicon, can be selected from one or more of the metal's oxides, hydroxides, or salts. When T is silicon, its source can be one or more of silicon oxides, silicates, silicate esters, etc.

[0068] S200: The mixture is subjected to a first heat treatment under a protective atmosphere to obtain an intermediate product.

[0069] In this application, the purpose of subjecting the mixture to a first heat treatment under a protective atmosphere is to form a lithium-rich oxide, while simultaneously generating a first oxygen vacancy in the surface region of the lithium-rich oxide, or in some cases, simultaneously generating a second oxygen vacancy in the central region. Therefore, the intermediate product is a lithium-rich material having a first oxygen vacancy, or having both a first oxygen vacancy and a second oxygen vacancy.

[0070] In some embodiments, the protective atmosphere is a non-oxidizing atmosphere, including but not limited to one of vacuum, inert gas, and hydrogen atmosphere, wherein the inert atmosphere can be one or more of nitrogen, argon, helium, etc.

[0071] In some embodiments, the temperature of the first heat treatment is 500-900°C. As a non-limiting example, the temperature of the first heat treatment includes, but is not limited to, 500°C, 550°C, 600°C, 650°C, 750°C, 800°C, 850°C, or 900°C. Selecting the above temperature range for the first heat treatment can form the lithium-rich oxide of this application while simultaneously generating oxygen vacancies; below 500°C, the lithium-rich oxide of this application may not be formed; above 900°C, on the one hand, the lithium-rich oxide required for this application may not be formed, and on the other hand, the concentration of oxygen vacancies may be too high. In some embodiments, the duration of the first heat treatment is 6-48 hours. As a non-limiting example, the temperature of the first heat treatment includes, but is not limited to, 6 hours, 12 hours, 18 hours, 24 hours, 30 hours, 36 hours, 42 hours, or 48 hours. Selecting the above-mentioned time range for the first heat treatment can form the lithium-rich oxide in this application, while simultaneously generating oxygen vacancies. If the first heat treatment time is less than 6 hours, the lithium-rich oxide in this application may not be formed. If the first heat treatment time is greater than 48 hours, on the one hand, the lithium-rich oxide required for this application may not be formed, and on the other hand, the concentration of oxygen vacancies may be too high. As a possible example, the temperature of the first heat treatment is between 600-800°C, and the time of the first heat treatment is 15-30 hours.

[0072] In some implementation schemes, the location of oxygen vacancies can be controlled by adjusting the temperature and duration of the first heat treatment. For example, when only the first oxygen vacancies need to be generated in the surface region, the temperature of the first heat treatment is 500-650°C, and the duration is 6-12 hours; while when both the first and second oxygen vacancies need to be generated in the surface region and the central region, the temperature of the first heat treatment is 650-900°C, and the duration is 12-48 hours.

[0073] In some implementations, the first heat treatment equipment may be any one of a rotary furnace, tumbler furnace, box furnace, tube furnace, roller kiln, pusher kiln, or fluidized bed.

[0074] S300: The intermediate product is subjected to a second heat treatment in an oxygen-rich atmosphere, and after cooling, a lithium-rich material is obtained; the temperature of the second heat treatment is lower than the temperature of the first heat treatment.

[0075] In this application, the purpose of subjecting the intermediate product to a second heat treatment in an oxygen-enriched atmosphere is to block oxygen vacancies on the intermediate product from the outside in, resulting in a gradient distribution of oxygen vacancy concentration on the intermediate product, that is, a gradual decrease in oxygen vacancy concentration from the side closer to the central region to the side farther from the central region. Here, in some cases (e.g., when oxygen vacancies are only present in the surface region), the oxygen vacancy is the first oxygen vacancy; in other cases (e.g., when oxygen vacancies are present in both the surface and central regions), it is the first oxygen vacancy and the second oxygen vacancy.

[0076] In some embodiments, the oxygen-enriched atmosphere is pure oxygen; in other embodiments, the oxygen-enriched atmosphere is a mixture of oxygen and an inert gas. As possible examples, the oxygen volume percentage in the oxygen-enriched atmosphere is between 50% and 100%, for example, the oxygen volume percentage in the oxygen-enriched atmosphere includes, but is not limited to, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%. When the oxygen volume percentage in the oxygen-enriched atmosphere is within the above range, oxygen vacancies on the intermediate product can be blocked from the outside in, resulting in a gradient distribution of oxygen vacancy concentration on the intermediate product, that is, the oxygen vacancy concentration gradually decreases from the side closer to the center region to the side farther from the center region. When the oxygen volume percentage in the oxygen-enriched atmosphere is less than 50%, the blocking effect of oxygen vacancies from the outside in is weakened.

[0077] In this application, the degree of influence of the oxygen-enriched atmosphere varies depending on the distance from the center of the central region, with the outermost region being more significantly affected, resulting in a lower oxygen vacancy concentration towards the surface. Furthermore, the oxygen vacancy concentration can be adjusted by gradually increasing the oxygen content. Therefore, in some embodiments, the initial oxygen volume percentage in the oxygen-enriched atmosphere is j%, followed by a gradual increase in the oxygen volume percentage at k% / min, where 50 ≤ j < 100, and 0 < k ≤ 2. As a non-limiting example, the initial oxygen volume percentage in the oxygen-enriched atmosphere includes, but is not limited to, 50%, 60%, 70%, 80%, 90%, or 99.999%, and the oxygen volume percentage increases at rates such as 0.1% / min, 0.5% / min, 1% / min, 1.5% / min, or 2% / min. Increasing the oxygen volume percentage in the oxygen-enriched atmosphere at the aforementioned rates allows control over the gradual decrease of oxygen vacancy concentration from the side closer to the center of the region to the side farther from the center.

[0078] In some embodiments, the temperature of the second heat treatment is 200-500°C. As a non-limiting example, the temperature of the second heat treatment includes, but is not limited to, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, or 500°C. Selecting the above temperature range for the first heat treatment can effectively block the oxygen vacancies generated during the first heat treatment process in an oxygen-enriched atmosphere, forming a distribution trend of gradually decreasing oxygen vacancy concentration from the inside out. It can also ensure that the oxygen vacancy concentration after the second heat treatment meets the oxygen vacancy concentration requirements of this application, thereby effectively reducing the diffusion of surface oxygen vacancies into the interior and the resulting structural instability and continuous oxygen and gas production. Below 200°C, the oxygen-enriched atmosphere may not be able to block the oxygen vacancies formed during the first heat treatment; above 500°C, new oxygen vacancies may be generated, making it difficult to block the oxygen vacancies generated during the first heat treatment process using an oxygen-enriched atmosphere, thus failing to form a distribution trend of gradually decreasing oxygen vacancy concentration from the inside out. In some embodiments, the time for the second heat treatment is 1-10 hours. By way of non-limiting example, the duration of the second heat treatment includes, but is not limited to, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours. As a possible example, the temperature of the second heat treatment is 300-400°C, and the duration is 4-7 hours. If the second heat treatment duration is greater than 10 hours in an oxygen-rich atmosphere, it may completely seal all the oxygen vacancies formed in the first heat treatment; if the second heat treatment duration is less than 1 hour, it may not be sufficient to seal all the oxygen vacancies formed in the first heat treatment.

[0079] In some implementations, the second heat treatment equipment can be any one of a rotary furnace, tumbler furnace, box furnace, tube furnace, roller kiln, pusher kiln, or fluidized bed.

[0080] In some embodiments, the second heat treatment and the first heat treatment can be performed in the same heat treatment equipment. After the first heat treatment, the temperature inside the heat treatment equipment is reduced to within the temperature range of the second heat treatment by a programmed cooling method. In other embodiments, the second heat treatment and the first heat treatment can be performed in two separate heat treatment equipment.

[0081] In some implementations, cooling after the second heat treatment refers to obtaining lithium-rich materials at room temperature.

[0082] In some embodiments, the method for preparing the lithium-rich additive of this application further includes the step of forming a coating layer on the surface of a lithium-rich material. As a non-limiting example, methods for forming a coating layer on the surface of a lithium-rich material include, but are not limited to, at least one of the following: sol-gel method, solution method, solid-phase method, and chemical vapor deposition (CVD).

[0083] In some embodiments, the mass of the coating layer includes, but is not limited to, 0.5-10% of the mass of the lithium-rich material. By way of non-limiting example, the mass of the coating layer is 0.5%, 3%, 5%, 7%, or 10% of the mass of the lithium-rich material.

[0084] The lithium-rich cathode of this application embodiment includes a cathode active material and a lithium supplementation additive of this application embodiment or a lithium supplementation additive prepared by the method of preparing the lithium supplementation additive of this application.

[0085] In some embodiments, the lithium supplementation additive accounts for 0.5-15 wt% of the total lithium-rich cathode. By way of non-limiting example, the lithium supplementation additive accounts for 3 wt%, 6 wt%, 9 wt%, 12 wt%, or 15 wt% of the total lithium-rich cathode.

[0086] In some implementations, in addition to the positive electrode active material and lithium supplementation additives, the lithium-rich positive electrode may also include at least one of the following: a positive electrode conductive agent and a binder. The positive electrode active material includes, but is not limited to, one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, lithium fluorinated vanadium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide. The positive electrode active material is capable of lithium intercalation and deintercalation, alloying and dealloying, or plating and stripping. The positive electrode conductive agent includes, but is not limited to, one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes. Adding a positive electrode conductive agent to the positive electrode material can enhance the conductivity of the electrode material layer, improve the conductivity of the lithium supplementation material, and facilitate electron and ion transport. The binder includes, but is not limited to, one or more of polyvinylidene fluoride (PVDF), sodium alginate, sodium carboxymethyl cellulose, and polyacrylic acid.

[0087] In some embodiments, the lithium-rich cathode also includes a current collector, which may be selected to contain aluminum or any other suitable conductive metal foil (e.g., solid, mesh, or covered foil), a metal grid or screen, or a porous metal. In some variations, the surface of the current collector may contain a surface-treated (e.g., carbon-coated and / or etched) metal foil.

[0088] The secondary battery of this application embodiment includes a positive electrode, a negative electrode, and a separator, wherein the positive electrode is a lithium-rich positive electrode of this application embodiment.

[0089] In some implementations, the positive electrode, separator, and negative electrode can be processed using a stacking or winding process to form a secondary battery. It should be noted that the secondary batteries in this application include, but are not limited to, lithium-ion batteries.

[0090] The secondary battery of this application embodiment can be widely used in new energy vehicles, aerospace, electronic products and other fields.

[0091] The preparation method of the lithium supplementation additive, the lithium-rich cathode, and the secondary battery of the embodiments of this application all have the beneficial effects of the lithium supplementation additive of the embodiments of this application.

[0092] The following non-limiting embodiments further illustrate certain features of the present technology.

[0093] Example 1

[0094] like Figure 3 As shown, the lithium supplement additive of this embodiment includes lithium-rich material Li5FeO4 and a coating layer covering the outer surface of the lithium-rich material Li5FeO4. The radius D50 of the Li5FeO4 particles is 7 μm. The particle structure of the Li5FeO4 includes a central region and a surface region arranged sequentially from the inside out. The average radius of the central region is 3 / 5 of the average radius of the Li5FeO4 particles, and the thickness of the surface region is 2 / 5 of the average radius of the Li5FeO4 particles. The surface region contains oxygen vacancies, accounting for 0.5 at% of all oxygen atoms in the Li5FeO4. Specifically, the surface region is divided into multiple layers, and the content of oxygen vacancies exhibits a gradient distribution, with the concentration decreasing layer by layer from the side closer to the central region to the side farther from the central region. The coating layer is made of graphene, and its mass is 2.5% of the mass of the Li5FeO4 particles.

[0095] The preparation method of the lithium supplement additive in this embodiment is as follows:

[0096] Step 1: Mix the lithium source and iron source evenly at a molar ratio of 5.1:1, and perform the first heat treatment in a tube furnace at 750°C for 10 hours under an argon atmosphere.

[0097] Step 2: After cooling to 400℃, the argon atmosphere was changed to a pure oxygen atmosphere (a mixture of oxygen and nitrogen, with oxygen accounting for 80% by volume), and the atmosphere was kept at this temperature for 6 hours (second heat treatment). The temperature was then lowered to room temperature to obtain the lithium-rich material Li5FeO4.

[0098] Step 3: Then, graphene N-methylpyrrolidone dispersion was added at a coating amount of 2.5% of the mass of lithium-rich material Li5FeO4, and stirred and mixed with lithium-rich material Li5FeO4 for 2 hours. After spray drying, a coating layer was formed, and the lithium supplementation additive of this embodiment was obtained.

[0099] Example 2

[0100] The lithium supplement additive provided in this embodiment differs from that in Example 1 in that oxygen vacancies account for 2 at% of all oxygen atoms in Li5FeO4, while the rest are the same.

[0101] The difference between the preparation method of the lithium supplement additive in this embodiment and that in Example 1 is that the volume ratio of oxygen in the oxygen-enriched atmosphere in step 2 is 70%, the heat treatment temperature is 400℃, and the holding time is 6h, while the other steps remain the same.

[0102] Example 3

[0103] The lithium supplement additive provided in this embodiment differs from that in Example 1 in that oxygen vacancies account for 5 at% of all oxygen atoms in Li5FeO4, while the others are the same.

[0104] The difference between the preparation method of the lithium supplement additive in this embodiment and that in Example 1 is that the volume ratio of oxygen in the oxygen-enriched atmosphere in step 2 is 60%, the heat treatment temperature is 400℃, and the holding time is 6h, while the other steps remain the same.

[0105] Example 4

[0106] The difference between the lithium supplement additive provided in this embodiment and that in Example 1 is that oxygen vacancies account for 10 at% of all oxygen atoms in Li5FeO4, while the rest are the same.

[0107] The difference between the preparation method of the lithium supplement additive in this embodiment and that in Example 1 is that the volume ratio of oxygen in the oxygen-enriched atmosphere in step 2 is 50%, the heat treatment temperature is 400℃, and the holding time is 6h, while the other steps remain the same.

[0108] Example 5

[0109] The difference between the lithium supplement additive provided in this embodiment and that in Example 3 is that the surface of the lithium-rich material does not contain a carbon coating layer, but otherwise they are the same.

[0110] The difference between the preparation method of the lithium supplement additive in this embodiment and that in Example 3 is that step 3 is omitted, while the other steps remain the same.

[0111] Example 6

[0112] The difference between the lithium supplement additive provided in this embodiment and that in Example 3 is that the lithium-rich material is Li. w O, where w = 2, and the rest are the same.

[0113] The difference between the preparation method of the lithium supplement additive in this embodiment and that in Example 3 is that step 1 is changed to: mixing the lithium source and hydrogen peroxide at a molar ratio of 2:1, stirring and reacting at 50°C for 1 hour. The solid particles are then separated and subjected to a first heat treatment at 650°C in a tube furnace under an argon atmosphere for 10 hours, while the other steps remain the same.

[0114] Example 7

[0115] The difference between the lithium supplement additive provided in this embodiment and that in Example 4 is that the oxygen vacancy accounts for 1.5 at% of all oxygen atoms in Li5FeO4, while the others are the same.

[0116] The difference between the preparation method of the lithium supplement additive in this embodiment and that in Example 4 is that the volume ratio of oxygen in the oxygen-enriched atmosphere in step 2 is initially 50%, and then increased to 80% at a rate of 0.5% / min. The heat treatment temperature is 400℃ and the holding time is 6h. Other steps remain the same.

[0117] Comparative Example 1

[0118] The lithium supplement additive provided in this comparative example differs from that in Example 3 in that the surface region contains oxygen vacancies, with the oxygen vacancy content accounting for 5 at% of all oxygen atoms in Li5FeO4, but the oxygen vacancies are not distributed regularly, while the rest are the same.

[0119] The difference between the preparation method of this comparative lithium supplement additive and Example 3 is that the first heat treatment temperature in step 1 is 600℃, the oxygen-enriched atmosphere in step 2 is changed to an argon atmosphere, and the other steps remain the same.

[0120] Battery assembly:

[0121] ① Positive electrode: N-methylpyrrolidone, lithium iron phosphate, lithium supplementation additive, conductive agent Super P and polyvinylidene fluoride are mixed in a mass ratio of 100:93:2:2:3 and ball-milled to obtain a positive electrode slurry. The ball milling time is 60 min and the speed is 30 Hz. The positive electrode slurry is coated on the surface of aluminum foil, rolled and then vacuum dried at 100℃ overnight to obtain a positive electrode sheet.

[0122] ② Negative electrode: The negative electrode active material (graphite), conductive agent (conductive carbon black, Super P), thickener (carboxymethyl cellulose, CMC), and binder (styrene-butadiene rubber, SBR) are mixed evenly in deionized water at a mass ratio of 95:2:0.5:2.5 to prepare a negative electrode slurry. The negative electrode slurry is coated on the surface of the current collector copper foil. After drying-rolling-secondary drying process, the negative electrode sheet is obtained.

[0123] ③ Electrolyte: Mix ethylene carbonate (EC) and ethyl methyl carbonate (DEC) in a volume ratio of 3:7, and add LiPF6 to form an electrolyte with a concentration of 1 mol / L.

[0124] ④Separator: Polyethylene (PE) microporous separator.

[0125] ⑤ Lithium-ion battery assembly: Lithium-ion batteries were assembled in an inert atmosphere glove box according to the assembly sequence of lithium anode-separator-electrolyte-cathode. The lithium-ion batteries corresponding to the lithium replenishment additives in Examples 1-7 are batteries A1-A7, and the lithium-ion battery corresponding to the lithium replenishment additive in Comparative Example 1 is battery B1.

[0126] B Performance Test:

[0127] The electrochemical performance of lithium-ion batteries A1-A7 corresponding to the lithium replenishment additives of Examples 1-7 and lithium-ion battery B1 corresponding to the lithium replenishment additive of Comparative Example 1 was tested. The test conditions were as follows: the assembled batteries were placed at room temperature for 6 hours and then charged and discharged. The charge and discharge voltage was 2.0-3.75V and the rate was 0.2C.

[0128] The test results are shown in Table 1 below:

[0129] Table 1 shows the electrochemical performance test results of the lithium-ion batteries corresponding to the lithium supplementation additives in Examples 1-7 and Comparative Example 1.

[0130]

[0131]

[0132] As shown in Table 1, the first-cycle gas production of batteries A1-A7 corresponding to the lithium-replenishing additives provided in Examples 1-7 of this application is significantly lower than that of battery B1 corresponding to the lithium-replenishing additive provided in Comparative Example 1. The first-cycle charge specific capacity, first-cycle discharge specific capacity, and first coulombic efficiency of batteries A1-A7 corresponding to the lithium-replenishing additives provided in Examples 1-7 are also significantly higher than those of battery B1 corresponding to the lithium-replenishing additive provided in Comparative Example 1. This is because the oxygen vacancy concentration formed on the surface of the lithium-rich material in the embodiments of this application gradually decreases from the inside to the outside, which can effectively suppress the diffusion of surface oxygen vacancies into the interior, reduce structural instability caused by oxygen vacancy diffusion, side reactions with the electrolyte, and continuous gas production. This allows the lithium-replenishing additive to fully exert its lithium-replenishing effect in the battery, thereby improving the first-cycle charge / discharge capacity and coulombic efficiency of the battery.

[0133] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0134] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0135] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between components; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0136] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0137] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0138] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A lithium supplement additive, characterized in that, The material includes lithium-rich materials, wherein the lithium-rich materials are lithium-rich oxides; the particle structure of the lithium-rich materials includes a central region and a surface region arranged sequentially from the inside out, wherein the surface region contains a first oxygen vacancy, and the concentration of the first oxygen vacancy gradually decreases from the side closer to the central region to the side farther away from the central region.

2. The lithium supplement additive according to claim 1, characterized in that, The first oxygen vacancy accounts for 0.5-10.0 at of all oxygen atoms in the lithium-rich oxide.

3. The lithium supplement additive according to claim 1, characterized in that, The average radius of the central region is 3 / 5 to 2 / 5 of the average radius of the lithium-rich material particles, and the thickness of the surface region is 2 / 5 to 3 / 5 of the average radius of the lithium-rich material particles. And / or, the median particle size of the lithium-rich material particles is between 1 and 30 μm, and the average radius of the lithium-rich material particles is between 0.5 and 15 μm.

4. The lithium supplement additive according to claim 1, characterized in that, The surface region includes at least two sub-surface regions with different first oxygen vacancy concentrations; wherein the sub-surface region with a higher first oxygen vacancy concentration is located closer to the central region, and the sub-surface region with a lower first oxygen vacancy concentration is located further away from the central region. The first oxygen vacancy concentration in the sub-surface region farthest from the central region is 0-1.0 at.

5. The lithium supplement additive according to claim 1, characterized in that, The central region has a second oxygen vacancy; the second oxygen vacancy accounts for 0-5 at of all oxygen atoms in the lithium-rich oxide.

6. The lithium supplement additive according to claim 1, characterized in that, The lithium-rich oxide includes those with the molecular formula Li. x M y T z O q The material and / or the molecular formula is Li w O materials; Wherein, M includes at least one of Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti and Mg, and T includes at least one of Fe, Co, Mn, Ni, Si and Al, and 0 < x ≤ 6, 0 < y ≤ 1, 0 ≤ z ≤ 2, 0 < q ≤ 5, 1 ≤ w ≤ 2.

7. The lithium supplement additive according to claim 1 or 5, characterized in that, It also includes a coating layer disposed on the surface of the surface region on the side away from the central region.

8. A method for preparing a lithium supplement additive as described in any one of claims 1 to 7, characterized in that, include: The lithium source, M source, and T source are mixed in a certain proportion to obtain a mixture; The mixture was subjected to a first heat treatment under a protective atmosphere to obtain an intermediate product; The intermediate product is subjected to a second heat treatment in an oxygen-rich atmosphere to obtain the lithium-rich material. in: The M element in the M source includes at least one of Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti, and Mg; and the T element in the T source includes at least one of Fe, Co, Mn, Ni, Si, and Al. The temperature of the second heat treatment is lower than the temperature of the first heat treatment.

9. The method for preparing the lithium supplement additive according to claim 8, characterized in that, The temperature of the first heat treatment is 500-900℃, and the time of the first heat treatment is 6-48h; And / or, the protective atmosphere is one of vacuum, inert gas, or hydrogen atmosphere.

10. The method for preparing the lithium supplementation additive according to claim 8, characterized in that: The oxygen-enriched atmosphere is pure oxygen or a mixture of oxygen and inert gas; when the oxygen-enriched atmosphere is a mixture of oxygen and inert gas, the volume percentage of oxygen in the oxygen-enriched atmosphere is between 50% and 100%. And / or, the temperature of the second heat treatment is 200-500℃, and the time of the second heat treatment is 1-10h.

11. The method for preparing the lithium supplementation additive according to claim 10, characterized in that: When the oxygen-enriched atmosphere is a mixture of oxygen and inert gas, the initial oxygen volume percentage in the oxygen-enriched atmosphere is j%, and then the oxygen volume percentage gradually increases at k% / min, where 50≦j<100 and 0<k≤2.

12. A lithium-rich cathode, characterized in that, The lithium-rich cathode comprises a cathode active material and a lithium-replenishing additive as described in any one of claims 1-7 or a lithium-replenishing additive prepared by the method described in any one of claims 8-11.

13. A secondary battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that, The cathode is the lithium-rich cathode as described in claim 12.

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