Positive electrode lithium supplement material, and preparation method therefor and use thereof

Abstract

A positive electrode lithium supplement material, and a preparation method therefor and a use thereof. The positive electrode lithium supplement material is a non-stoichiometric compound, and the chemical composition of the positive electrode lithium supplement material is Li2-xMn1-yMyO3, wherein M is a doping element, 0<x≤0.2, and 0≤y≤0.2; and the valence state of M is not +4, or, a pure-phase lithium oxide of M is isomeric with a layered Li2MnO3 material. The positive electrode lithium supplement material has a good lithium supplement effect, and also has a low activation difficulty and an excellent interface stability.

Description

A positive electrode lithium supplementing material, a preparation method and application thereof TECHNICAL FIELD

[0001] The present application relates to a lithium supplementing material, in particular to a positive electrode lithium supplementing material, a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. BACKGROUND

[0002] Lithium supplementing technology for lithium ion batteries is an important means to improve the energy density of batteries. During the first charging process of lithium ion batteries, organic electrolyte will undergo redox decomposition at the electrode interface to form a solid electrolyte film, consuming a large amount of active lithium, resulting in low first-cycle coulombic efficiency of the battery and reducing the capacity and energy density of the lithium ion battery. In addition, redox decomposition at the electrode interface also continuously occurs during the cycling process, continuously consuming active lithium, leading to continuous decline in the capacity and energy density of the battery.

[0003] Lithium supplementing technology is a technology for supplementing additional active lithium to lithium ion batteries to offset the energy density decay caused by the consumption of active lithium. The current lithium supplementing technology can be divided into two categories: positive electrode lithium supplementing and negative electrode lithium supplementing. Among them, negative electrode lithium supplementing mainly includes the following lithium supplementing methods: (1) negative electrode chemical lithium supplementing, the material for lithium intercalation is generally n-butyl lithium hexane solution or potassium iodide acetonitrile solution, and the lithiation agent used in chemical lithium supplementing technology generally has toxicity and danger; (2) negative electrode lithium metal self-discharge lithium supplementing, lithium sheet or lithium powder is directly pressed on the negative electrode, this method has great process difficulty and high activity of lithium metal, which has certain danger; (3) negative electrode electrochemical lithium supplementing, a metal lithium is introduced to form a counter electrode with the negative electrode, and the depth of electrochemical charging and discharging is controlled to realize pre-lithiation of the negative electrode sheet, this method has the most complex process operation and is not easy to be used for mass production. In summary, negative electrode lithium supplementing has great difficulty and danger, and is difficult to be industrialized. Positive electrode lithium supplementing is to add a compound that is easy to be delithiated at high voltage in the positive electrode, and to supplement active lithium to the battery cell by using high voltage in the formation charging process. Since most positive electrode lithium supplementing agents are safe, they are widely used in the industry.

[0004] However, the commonly used lithium supplementing agents such as lithium ferrite and lithium nickelate have high raw material cost and poor interface stability. They are unstable in air, and exposure to air will cause rapid capacity decay or even failure, which is difficult to store.

[0005] SUMMARY

[0006] The present application provides a positive electrode lithium supplementing material, which has good lithium supplementing effect, low activation voltage and excellent interface stability.

[0007] This application also provides a method for preparing a positive electrode lithium replenishment material. This method involves mixing and sintering a lithium source, a manganese source, and a compound of dopant element M in a specific design ratio to obtain the aforementioned positive electrode lithium replenishment material that has both good lithium replenishment effect, low activation voltage, and excellent interface stability.

[0008] This application also provides a positive electrode sheet, including the above-mentioned positive electrode lithium replenishment material, which has the advantages of strong stability and good lithium replenishment effect.

[0009] This application also provides a lithium-ion battery including the above-mentioned positive electrode, which has excellent first-cycle coulombic efficiency and cycle capacity retention.

[0010] The first aspect of this application provides a positive electrode lithium replenishment material, wherein the positive electrode lithium replenishment material is a non-stoichiometric compound, and the chemical composition of the positive electrode lithium replenishment material is Li. 2-x Mn 1-y M y O3, where M is a dopant element, 0 < x ≤ 0.2, 0 ≤ y ≤ 0.2;

[0011] The valence state of M is not +4, or the pure-phase lithium oxide of M is isomerized with the layered Li2MnO3 material.

[0012] The positive electrode lithium replenishment material as described above, wherein M includes one or more of Mg, Al, Ti, V, Cr, Fe, Co, Ni, Zn, Sr, Y, Zr, Nb, Mo, and W.

[0013] The positive electrode lithium replenishment material as described above, wherein the positive electrode lithium replenishment material is a primary particle.

[0014] The positive electrode lithium replenishment material as described above, wherein the D50 particle size of the positive electrode lithium replenishment material is 0.1μm to 2μm.

[0015] The cathode lithium replenishment material described above, wherein the specific surface area of ​​the cathode lithium replenishment material is 0.5 m². 2 / g~24m 2 / g.

[0016] A second aspect of this application provides a method for preparing the positive electrode lithium replenishment material as described above, wherein the preparation method includes the following steps:

[0017] 1) The manganese source, lithium source, and compound containing doped element M are mixed according to the designed ratio to obtain a mixture;

[0018] 2) The mixture is sintered to obtain the positive electrode lithium replenishment material.

[0019] The preparation method described above, wherein the mixing process is carried out under solid-phase conditions.

[0020] The preparation method as described above, wherein the sintering treatment comprises primary sintering and secondary sintering performed in sequence;

[0021] The temperature of the primary sintering is 450-600℃, and the sintering time is 4-8h;

[0022] The temperature of the secondary sintering is 750-950℃, and the sintering time is 6-12h.

[0023] The third aspect of the present application provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode lithium supplementing material provided in the first aspect of the present application.

[0024] The fourth aspect of the present application provides a lithium ion battery, comprising the positive electrode sheet provided in the third aspect of the present application.

[0025] The implementation of the present application has at least the following advantages:

[0026] Compared with the conventional positive electrode lithium supplementing materials such as lithium ferrite and lithium nickelate, the positive electrode lithium supplementing material provided in the present application is a manganese-based compound, which has ultra-high interface stability and can maintain activity for a long time in air, is easy to store, and the composition of the positive electrode lithium supplementing material is in non-stoichiometric ratio and optionally isovalent isomerization doped in the present application, so that the positive electrode lithium supplementing material is rich in defects, thereby reducing the activation difficulty of the manganese-based lithium supplementing material, and the activation voltage is matched with the working voltage of the conventional high-voltage battery. In addition, manganese ore is abundant in nature, and the raw material cost is much lower than that of lithium ferrite and lithium nickelate and other lithium supplementing materials. Therefore, the positive electrode lithium supplementing material of the present application has good lithium supplementing effect, and also has low cost, small activation difficulty and excellent interface stability. BRIEF DESCRIPTION OF DRAWINGS

[0027] Fig. 1 is an XRD graph of Li2MnO3 pure phase material;

[0028] Fig. 2 is an XRD graph of LiCoO2 pure phase material;

[0029] Fig. 3 is an SEM graph of the positive electrode lithium supplementing material of Example 1. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0031] The first aspect of the application provides a positive electrode lithium supplement material, which is a non-stoichiometric compound, and the chemical composition is Li 2-x Mn 1-y M y O3, wherein M is a doping element, 0

[0032] The valence of M is not +4, or the pure phase lithium oxide of M is isomorphic with the layered Li2MnO3 material.

[0033] Compared with the conventional lithium ferrite, lithium nickelate and other positive electrode lithium supplement materials, the positive electrode lithium supplement material provided by the application is a manganese-based compound, which has ultra-high interface stability and can maintain activity for a long time in air, and the manganese ore is rich in resources in nature, and the raw material cost is much lower than that of lithium ferrite and lithium nickelate and other lithium supplement materials. However, the conventional manganese-based lithium supplement material has too strong stability and needs to be activated at a high voltage of >5.5 V, and even the activation efficiency is still not high at a high voltage, which does not match the working voltage interval of the conventional high-voltage battery. The composition of the positive electrode lithium supplement material is controlled by the application, which greatly reduces the activation difficulty of the manganese-based lithium supplement material, so that it can complete the activity at a voltage of not higher than 4.8 V, which is better matched with the working voltage of the conventional high-voltage battery.

[0034] The composition of the positive electrode lithium supplement material is controlled by the application, which is embodied in two aspects of non-stoichiometric ratio control and optional doping control.

[0035] The non-stoichiometric ratio control means that the positive electrode lithium supplement material of the application is a non-stoichiometric compound, and the non-stoichiometric ratio means that the sum of the positive valence of the cations in the chemical formula Li 2-x Mn 1-y M y O3 is not equal to the sum of the negative valence of the anions, for example, when y is 0, the chemical composition satisfying the stoichiometric ratio should be Li2MnO3, and the application limits the subscript of Li to 2-x and x>0, so that the composition does not satisfy the stoichiometric ratio, thereby generating a certain lithium vacancy and reducing the activation difficulty of the positive electrode lithium supplement material.

[0036] The doping control refers to that the element M doped in the positive electrode material is heterovalent with the base Mn element, or the pure phase lithium oxide of the element M is isomorphic with the layered Li2MnO3 material, wherein the heterovalent refers to that the valence of the element M is different from that of the Mn element, i.e. the valence of the element M is not +4, and the isomorphic refers to that the lithium oxide of the element M does not belong to the layered structure with the space group C2 / m, which can be verified by XRD test and spectrum peak indexation of the space group attribution of the material structure. Taking the element M as the Co element as an example, FIG. 1 is an XRD diagram of a Li2MnO3 pure phase material, and FIG. 2 is an XRD diagram of a LiCoO2 pure phase material. It can be known by spectrum peak indexation of FIG. 1 and FIG. 2 that the Li2MnO3 is of the space group C2 / m, and the LiCoO2 is of the space group R-3m. The typical difference between the two is that the material with the space group C2 / m will appear a superlattice peak of 20-35° under the Cu target test condition, thereby verifying that the pure phase lithium oxide compound of the Co element is isomorphic with the layered Li2MnO3 material.

[0037] The doping control can form a local multi-phase structure in the material, reduce the size of the Li2MnO3 structure crystal domain, and play a role similar to grain refinement. In addition, the local multi-phase crystal formed by doping has more crystal boundaries, which is beneficial to lithium ion conduction, thereby reducing the activation difficulty of the positive electrode lithium supplement material.

[0038] By controlling x to satisfy 0

[0039] In summary, the positive electrode lithium supplement material provided by the application not only has good lithium supplement effect, but also has lower cost, smaller activation difficulty and excellent interface stability, which is convenient for storage and industrial application.

[0040] In a preferred embodiment, M includes one or more of Mg, Al, Ti, V, Cr, Fe, Co, Ni, Zn, Sr, Y, Zr, Nb, Mo, W. The above elements are not only beneficial to the construction of defects to reduce the activation difficulty of the positive electrode lithium supplement material, but also have good compatibility with the Li2MnO3 material of the body, which is beneficial to uniform doping and is not easy to precipitate or form a segregation compound.

[0041] In a preferred embodiment, the positive electrode lithium supplement material of the application is a primary particle. Compared with a secondary particle, the primary particle can exhibit higher irreversible capacity and better lithium supplement.

[0042] In a preferred embodiment, the D50 particle size of the positive electrode lithium supplementing material of the present application is 0.1 μm to 2 μm, specifically 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 0.9 μm, 1.1 μm, 1.3 μm, 1.5 μm, 1.7 μm, 2 μm or a range value between any two of the above values. When the D50 particle size of the positive electrode lithium supplementing material is less than 0.1 μm, the contact area with the electrolyte is too large, which easily leads to decomposition and gas generation; when the D50 particle size of the positive electrode lithium supplementing material is greater than 2 μm, the lithium supplementing capacity is not easy to be exerted.

[0043] The specific surface area (BET) of the positive electrode lithium supplementing material is also a key factor affecting the battery performance. The greater the specific surface area, the more conducive to the activation of the lithium supplementing material and the exertion of the capacity, but too large specific surface area will lead to side reactions between the lithium supplementing material and the electrolyte to generate gas, which is not conducive to the cycle performance of the battery. Based on the above considerations, it is preferred that the specific surface area of the positive electrode lithium supplementing material is controlled to 0.5 m 2 / g to 24 m 2 / g, specifically 0.5 m 2 / g, 1.0 m 2 / g, 3.0 m 2 / g, 5.0 m 2 / g, 8.0 m 2 / g, 10.0 m 2 / g, 13.0 m 2 / g, 16.0 m 2 / g, 19.0 m 2 / g, 21.0 m 2 / g, 24.0 m 2 / g or a range value between any two of the above values.

[0044] The second aspect of the present application provides a preparation method of a positive electrode lithium supplementing material, wherein the preparation method comprises the following steps:

[0045] 1) mixing a manganese source, a lithium source and a compound containing a doping element M according to a designed ratio to obtain a mixture;

[0046] 2) sintering the mixture to obtain the positive electrode lithium supplementing material.

[0047] In step 1), the designed ratio refers to the molar ratio between the raw materials, which can make the chemical composition of the finally obtained positive electrode lithium supplementing material meet the composition of Li 2-x Mn 1-y M y O3, wherein 0 < x ≤ 0.2 and 0 ≤ y ≤ 0.2.

[0048] The chemical composition of the positive electrode lithium supplementing material is Li 1.95 Mn0.9 Co 0.1 In O3, where the doping element M is Co, the molar ratio of the lithium source, the manganese source and the compound containing the doping element Co should satisfy the molar ratio of Li element in the lithium source, Mn element in the manganese source and Co element in the compound containing the doping element Co is 1.95:0.9:0.1.

[0049] The present application does not make specific limitation on the types of the manganese source, the lithium source and the compound containing the doping element M, which can be selected from the manganese source, the lithium source and the compound containing the doping element M commonly used in lithium ion batteries. Specifically, the manganese source includes one or more of manganese monoxide (MnO), manganese dioxide (MnO2), dimanganese trioxide (Mn2O3), trimanganese tetraoxide (Mn3O4), manganese oxalate (MnC2O4) and hydrates of the above compounds; the lithium source includes one or more of lithium hydroxide (LiOH), lithium carbonate (Li2CO3) and hydrates of the above compounds; the compound containing the doping element M includes one or more of oxides, hydroxides, chlorides, sulfates, nitrates, acetates and carbonates of the element M.

[0050] In step 1), the mixing treatment is preferably mixing under solid phase condition, which means that the solid particles of the manganese source, the lithium source and the compound containing the doping element M are directly mixed without solvent. The sintering after mixing under solid phase condition is not only beneficial to obtaining the positive electrode lithium supplement material with the morphology of primary particles, but also beneficial to the large-scale industrial production of the positive electrode lithium supplement material.

[0051] The sintering treatment in step 2) can be performed according to the conventional sintering conditions in the art, and can be performed in air atmosphere or oxygen atmosphere.

[0052] In a preferred embodiment, the sintering treatment includes primary sintering and secondary sintering performed in sequence; the temperature of the primary sintering is 450-600°C, and the sintering time is 4-8h; the temperature of the secondary sintering is 750-950°C, and the sintering time is 6-12h.

[0053] The primary sintering is performed at a lower temperature, which is more beneficial to the formation of material defects; the secondary sintering is performed at a higher temperature, which is beneficial to the removal of the combined water on the surface of the material and the water in the interior of the material, thereby avoiding causing swelling in the use of the battery.

[0054] If the heating or cooling rate is too fast, it is easy to cause deformation of the material, thereby affecting the quality of the product; if the heating rate or the cooling rate is too slow, it will lead to too long processing time, thereby increasing the production cost. Based on the above considerations, the heating rate during sintering is controlled to be 2-10°C / min, and the cooling rate is controlled to be 2-5°C / min.

[0055] In addition, the ball milling treatment can be introduced before the first sintering and before the second sintering, which can make the raw materials of the first sintering and the second sintering more fully mixed, and is beneficial to obtain the positive electrode lithium supplement material with more uniform powder distribution and better consistency.

[0056] In a specific embodiment, the ball milling treatment before the first sintering includes ball milling the mixture at a speed of 300-600 rpm for 2-6 h using a ball mill; and the ball milling treatment before the second sintering includes ball milling the first sintered material at a speed of 600-1200 rpm for 2-6 h using a ball mill.

[0057] In order to obtain the positive electrode lithium supplement material with a designed size, after the sintering treatment is completed, a crushing treatment process is further included, in a specific embodiment, the crushing treatment includes ball milling at a speed of 300-800 rpm using a ball mill to the designed size.

[0058] Further, after the crushing treatment, the crushed material can be subjected to water washing and drying or re-sintering in order to remove the residual alkali and moisture on the surface. The re-sintering temperature can be controlled at 180-350 ℃, and the time is controlled at 2-6 h. After the water washing and drying treatment, the residual alkali amount on the surface of the positive electrode lithium supplement material satisfies: Li2CO3≤3.5 wt%, LiOH≤1.2 wt%. Within the above residual alkali content range, the gel-like substance can be avoided in the process of forming the slurry.

[0059] Further, after the water washing and drying, a magnetic removal process is further included, the magnetic removal can adopt the conventional operation in the art, as long as the content of the magnetic substance in the material is <50 ppb.

[0060] In addition, in order to obtain the positive electrode lithium supplement material with high size consistency, the material after sintering or ball milling can be subjected to a sieving treatment, and the sieving treatment is preferably performed using a 300-mesh sieve.

[0061] The third aspect of the present application provides a positive electrode sheet, which comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode lithium supplement material provided in the second aspect of the present application.

[0062] The positive electrode current collector is not specially limited in the present application, and the current collector conventionally used in the art can be used, such as an aluminum foil, which can be commercially available.

[0063] In addition to the above-mentioned positive electrode lithium supplementing material, the positive electrode active material layer of the present application further comprises a positive electrode active material, a conductive agent, a binder and the like. Among them, the positive electrode active material, the conductive agent and the binder can be selected from the substances conventionally used in the art. Specifically, the positive electrode active material can be selected from one or more of lithium-rich manganese-based positive electrode materials, nickel-manganese spinel materials, medium-low nickel ternary materials and cobaltite or other ternary materials used at high pressure. The conductive agent can be selected from one or more of conductive carbon black, acetylene black, ketjen black, carbon nanofiber. The binder can be selected from one or more of PVDF, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, butadiene rubber.

[0064] The more the positive electrode lithium supplementing material in the positive electrode active material layer, the better the excellent lithium supplementing effect can be achieved. However, too much supplementing material will inevitably lead to a decrease in the content of the positive electrode active material, which is not conducive to the improvement of the capacity of the positive electrode sheet and the energy density of the battery. Based on the above considerations, the mass content of the positive electrode active material in the positive electrode active material layer is not less than 94%, and the mass content of the positive electrode lithium supplementing material is 0.3% to 6%.

[0065] The preparation method of the positive electrode sheet of the present application is not particularly limited, and it can adopt the conventional preparation method in the art. For example, the positive electrode active material, the positive electrode lithium supplementing material, the conductive agent and the binder are dispersed in a solvent in a certain proportion to obtain a slurry, and then the slurry is coated on at least one surface of the positive electrode current collector, and after drying, cutting and rolling, the positive electrode sheet can be obtained.

[0066] The fourth aspect of the present application provides a lithium ion battery comprising the positive electrode sheet provided by the third aspect of the present application.

[0067] Since the lithium ion battery comprises a positive electrode sheet with a low activation voltage and a high interface stability lithium supplementing material, it can achieve stable and excellent lithium supplementing effect under conventional charge and discharge voltage, efficiently delithiate as a lithium source during the first charge process, and provide abundant lithium ions to make up for the irreversible lithium ions consumed during the formation of SEI film, thereby improving the first cycle coulombic efficiency and cycle capacity retention rate of the battery.

[0068] The lithium ion battery of the present application further comprises a negative electrode sheet, a separator and an electrolyte in addition to the positive electrode sheet.

[0069] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector. The negative electrode current collector can be selected from the negative electrode current collectors commonly used in the art, such as a copper foil. The negative electrode active material layer can also refer to the conventional composition in the art, for example, the negative electrode active material layer comprises a negative electrode active material, a conductive agent and a binder. The negative electrode active material can be selected from the negative electrode active materials commonly used in the art, including but not limited to one or more of natural graphite, artificial graphite, silicon-carbon material, silicon-oxygen material and hard carbon. The composition of the conductive agent and the binder can refer to the types of the conductive agent and the binder in the positive electrode sheet, which will not be described herein.

[0070] The preparation method of the negative electrode sheet is not particularly limited in the present application, and the conventional preparation method in the art can be used. For example, the negative electrode active material, the conductive agent and the binder are dispersed in a solvent in a certain proportion to obtain a slurry, and then the slurry is coated on at least one surface of the positive electrode current collector, and after drying, slitting and rolling, the negative electrode sheet is obtained.

[0071] The function of the separator is to separate the positive electrode sheet and the negative electrode sheet and provide a channel for the migration of lithium ions. The type of the separator is not particularly limited in the present application, and the separator commonly used in the art can be used, such as a polypropylene separator, a polyethylene separator and the like.

[0072] The type of the electrolyte is also not particularly limited in the present application, and can be selected from the liquid electrolyte, the solid electrolyte or the gel-type polymer electrolyte commonly used in the art.

[0073] The lithium ion battery of the present application can be prepared by referring to the conventional method in the art, for example, the positive electrode sheet, the separator and the negative electrode sheet are sequentially stacked to obtain an electric core by the lamination or winding process, and then the lithium ion battery of the present application is obtained by the processes of baking, liquid injection, formation, packaging and the like.

[0074] Hereinafter, the positive electrode lithium supplementing material, the preparation method and the application thereof of the present application will be described in detail through specific examples.

[0075] Example 1

[0076] The chemical composition of the positive electrode lithium supplementing material of the present embodiment is Li 1.95 MnO3, and the preparation method comprises the following steps:

[0077] 1) LiOH and MnO2 are mixed in a molar ratio of 1.95:1 to obtain sample P1;

[0078] 2) The sample P1 is finely mixed by using a ball mill at a speed of 400 rpm for 6 h to obtain sample P2;

[0079] 3) Put sample P2 into a muffle furnace, and heat to 600℃ at a heating rate of 5℃ / min under air atmosphere, and sinter for 4h, and then naturally cool to room temperature to obtain sample P3;

[0080] 4) Put sample P3 into a ball mill, and ball mill for 6h at a speed of 600rpm to obtain sample P4;

[0081] 5) Put sample P4 into a muffle furnace, and heat to 900℃ at a heating rate of 5℃ / min under air atmosphere, and sinter for 12h, and then naturally cool to room temperature to obtain sample P5;

[0082] 6) Put sample P5 into a ball mill, and ball mill to a D50 particle size of 0.8μm to obtain the positive electrode lithium supplement material.

[0083] Example 2

[0084] The chemical composition of the positive electrode lithium supplement material of the present example is Li 1.92 MnO3, and the preparation method is basically the same as that of Example 1, except that step 1) is: mixing LiOH, MnO2 according to a molar ratio of 1.92:1. The remaining steps are the same as those of Example 1.

[0085] Example 3

[0086] The chemical composition of the positive electrode lithium supplement material of the present example is Li 1.9 Mn 0.95 Co 0.05 O3, and the preparation method is basically the same as that of Example 1, except that step 1) is: mixing LiOH, MnO2, CoO according to a molar ratio of 1.9:0.95:0.05. The remaining steps are the same as those of Example 1.

[0087] Example 4

[0088] The chemical composition of the positive electrode lithium supplement material of the present example is Li 1.95 MnO3, and the preparation method is basically the same as that of Example 1, except that step 6) is: putting sample P5 into a ball mill, and ball milling to a D50 particle size of 1.5μm to obtain the positive electrode lithium supplement material.

[0089] Example 5

[0090] The chemical composition of the positive electrode lithium supplement material of the present example is Li 1.95 MnO3, and the preparation method is basically the same as that of Example 1, except that step 6) is: putting sample P5 into a ball mill, and ball milling to a D50 particle size of 3μm to obtain the positive electrode lithium supplement material.

[0091] Example 6

[0092] The chemical composition of the positive electrode lithium supplement material of the present example is Li 1.9 Mn 0.95 Mg 0.05 O3, the preparation method of which is basically the same as that of Example 3, except that step 1) is: LiOH, MnO2, MgO are mixed in a molar ratio of 1.9:0.95:0.05. The remaining steps are the same as those of Example 3.

[0093] Example 7

[0094] The chemical composition of the positive electrode lithium supplement material of the present example is Li 1.9 Mn 0.95 Mo 0.05 O3, the preparation method of which is basically the same as that of Example 3, except that step 1) is: LiOH, MnO2, MoO3 are mixed in a molar ratio of 1.9:0.95:0.05. The remaining steps are the same as those of Example 3.

[0095] Example 8

[0096] The chemical composition of the positive electrode lithium supplement material of the present example is Li 1.9 Mn 0.95 Ni 0.05 O3, the preparation method of which is basically the same as that of Example 3, except that step 1) is: LiOH, MnO2, NiO are mixed in a molar ratio of 1.9:0.95:0.05. The remaining steps are the same as those of Example 3.

[0097] Comparative Example 1

[0098] The chemical composition of the positive electrode lithium supplement material of the present example is Li2MnO3, the preparation method of which is basically the same as that of Example 1, except that step 1) is: LiOH, MnO2 are mixed in a molar ratio of 2:1. The remaining steps are the same as those of Example 1.

[0099] Comparative Example 2

[0100] The chemical composition of the positive electrode lithium supplement material of the present example is Li2NiO2, the preparation method of which comprises the following steps:

[0101] 1) Li2O and LiOH are mixed in a molar ratio of 1:1 to obtain a lithium source, and the lithium source and NiO are mixed in a molar ratio of Li / Ni=2:1 to obtain a mixture, and the mixture is ball milled at a speed of 800 rpm for 1 h using a ball mill to obtain a mixed powder;

[0102] 2) Put the mixed powder into a muffle furnace, and heat to 500℃ at a rate of 5℃ / min under inert atmosphere, keep for 2 hours, then heat to 740℃ at a rate of 5℃ / min, keep for 12 hours, and then cool to room temperature to obtain the sintered material;

[0103] 3) Ball mill the sintered material in inert atmosphere at a speed of 1000 rpm to obtain the positive electrode lithium supplement material with a D50 particle size of 1.5 μm.

[0104] Comparative Example 3

[0105] The chemical composition of the positive electrode lithium supplement material of the present comparative example is Li5FeO4, and the preparation method comprises the following steps:

[0106] 1) Mix Li2O and LiOH in a molar ratio of 1:1 to obtain a lithium source, and mix the lithium source and Fe2O3 in a molar ratio of Li / Fe = 5:1 to obtain a mixture, and use a ball mill to ball mill the mixture at a speed of 800 rpm for 1 h to obtain a mixed powder;

[0107] 2) Put the mixed powder into a muffle furnace, and heat to 500℃ at a rate of 5℃ / min under inert atmosphere, keep for 2 hours, then heat to 900℃ at a rate of 5℃ / min, keep for 6 hours, and then cool to room temperature to obtain the sintered material;

[0108] 3) Ball mill the sintered material in inert atmosphere at a speed of 1000 rpm to obtain the positive electrode lithium supplement material with a D50 particle size of 1.5 μm.

[0109] Comparative Example 4

[0110] The chemical composition of the positive electrode lithium supplement material of the present comparative example is Li 1.7 MnO3, and the preparation method is basically the same as that of Example 1, except that step 1) is: mix LiOH, MnO2 in a molar ratio of 1.7:1. The remaining steps are consistent with Example 1.

[0111] Comparative Example 5

[0112] The chemical composition of the positive electrode lithium supplement material of the present comparative example is Li 1.7 Mn 0.95 Co 0.05 O3, and the preparation method is basically the same as that of Example 1, except that step 1) is: mix LiOH, MnO2, CoO in a molar ratio of 1.7:0.95:0.05. The remaining steps are consistent with Example 1.

[0113] Comparative Example 6

[0114] The chemical composition of the positive electrode lithium supplement material of the present comparative example is Li2.0 Mn 0.95 Co 0.05 O3, the preparation method and example 1 are basically the same, the difference is that step 1) is: LiOH, MnO2, CoO is mixed according to the mole ratio of 2.0:0.95:0.05. The remaining steps are consistent with example 1.

[0115] Test example

[0116] I. The following performances of the positive electrode lithium supplement material of the above examples and comparative examples are tested:

[0117] A, specific surface area

[0118] Test method: refer to GB / T 19587-2004 "gas adsorption BET method for determination of specific surface area of solid matter (GB / T 19587-2004)". The test results are shown in table 1.

[0119] B, SEM test

[0120] Test method: scanning electron microscope is used to observe the morphology of the positive electrode lithium supplement material. Figure 3 is the SEM diagram of the positive electrode lithium supplement material of example 3, as shown in figure 3, the positive electrode material is primary particle, without obvious spherical or other secondary particle morphology.

[0121] II. The positive electrode lithium supplement material of the above examples and comparative examples is respectively made into positive electrode sheet, and then assembled into button cell with metal lithium negative electrode, electrolyte and separator according to the following method:

[0122] The positive electrode lithium supplement material, SP and PVDF are mixed according to the mass ratio of 80:10:10, and then dispersed in NMP solvent to obtain positive electrode slurry. The slurry is coated on aluminum foil current collector according to the area density of 3mg / cm 2 , dried, punched, rolled to obtain positive electrode sheet; the button cell shell, positive electrode sheet, PP separator and metal lithium sheet are stacked in turn, and then the electrolyte is added to obtain button cell;

[0123] Among them, the electrolyte includes solvent and lithium salt, the solvent is a mixture of EC, DMC and DEC with a volume ratio of 1:1:1, and the lithium salt is LiPF6, and the concentration of LiPF6 in the electrolyte is 1.0mol / L.

[0124] The following performances of the button cell assembled above are tested:

[0125] A, first circle irreversible capacity

[0126] Test method: freshly assembled button cell was charged and discharged at 20 mA / g in the range of 2.5-4.8 V, and the first cycle charge capacity C and the first cycle discharge capacity D were recorded. The first cycle irreversible capacity of the battery was calculated by Q1 = C-D.

[0127] The higher the first cycle irreversible capacity of the battery, the smaller the difficulty of activation of the positive electrode lithium supplement material, and the better the lithium supplement effect.

[0128] B. Air stability

[0129] Test method: the button cell was exposed to an environment with a temperature of 25°C and a humidity of 30% for 24 h, and then the sample was dried and charged and discharged at 20 mA / g in the range of 2.5-4.8 V. The first cycle irreversible capacity Q2 of the battery was recorded.

[0130] The capacity attenuation rate was calculated by the following formula:

[0131] Capacity attenuation rate = (Q1-Q2) / Q1 x 100%.

[0132] The smaller the capacity attenuation rate of the sample, the higher the air stability.

[0133] The above test results are shown in Table 1.

[0134] III. The positive electrode active materials of the above examples and comparative examples were respectively made into positive electrode sheets, and then graphite negative electrode, electrolyte and separator were used to form full cells according to the following method.

[0135] 1) Preparation of positive electrode sheet: Li 1.1 Ni 0.33 Co 0.05 Mn 0.52 O2, positive electrode lithium supplement material, SP and PVDF were mixed in a mass ratio of 96:0.5:1.5:2, and then a positive electrode slurry was obtained by dispersion in NMP solvent. The slurry was coated on an aluminum foil current collector at a surface density of 12 mg / cm 2 , dried, punched, and rolled to obtain a positive electrode sheet;

[0136] 2) Preparation of negative electrode sheet: artificial graphite, conductive agent SP and binder CMC were mixed in a mass ratio of 95:2.5:2.5, and then a negative electrode slurry was obtained by dispersion in water. The slurry was coated on a copper foil current collector at a surface density of 10 mg / cm 2 , dried, punched, and rolled to obtain a negative electrode sheet;

[0137] 3) Assembly of lithium ion battery: after the positive electrode sheet, PP separator and negative electrode sheet are sequentially stacked and placed, the battery cell is obtained by winding, then the battery cell is placed in an aluminum plastic film packaging bag, electrolyte is injected to seal, and the lithium ion battery is obtained after electrolyte formation;

[0138] The electrolyte comprises a lithium salt and a solvent, wherein the solvent is a mixture of EC, DMC, DEC, FEC and VC in a volume ratio of 30:30:20:18:2, and the lithium salt is LiPF6, and the concentration of LiPF6 is 1.0M.

[0139] The full battery assembled above is tested for the following performances:

[0140] A, the first circle charging gram capacity

[0141] Test method: at 25℃, the freshly assembled full battery is charged and discharged at a charge-discharge rate of 20mA / g in the range of 2.5-4.8V, and the first circle charging gram capacity of the battery is recorded.

[0142] B, the first circle coulombic efficiency

[0143] Test method: at 25℃, the freshly assembled full battery is charged and discharged at a charge-discharge rate of 20mA / g in the range of 2.5-4.8V, and the first circle charging gram capacity C of the battery is recorded, the first circle discharging gram capacity D is recorded, and the first circle coulombic efficiency η = D / C x 100%.

[0144] C, 25℃ cycle 100 weeks capacity retention rate

[0145] Test method: at 25℃, the freshly assembled full battery is charged and discharged at a charge-discharge rate of 20mA / g in the range of 2.5-4.8V, and the first circle discharging gram capacity D1 is recorded, the discharging gram capacity D2 of the battery when cycled to 100 weeks is recorded, and the 25℃ cycle 100 weeks capacity retention rate k = D2 / D1 x 100%.

[0146] The above test results are shown in Table 2.

[0147] Table 1

[0148] Table 2

[0149] From Table 1 and Table 2, the following conclusions can be drawn:

[0150] 1) From the comparison of Example 1 and Example 2, it can be seen that the degree of non-stoichiometric ratio of Example 2 is increased compared with Example 1, and the lithium vacancy defect is also increased, and from the performance test results, it can be seen that the first cycle irreversible capacity of Example 2 is increased, which represents the enhanced ability of lithium supplement; in addition, both Example 1 and 2 can maintain good air stability, and the capacity attenuation rate is less than 1%; at the same time, due to the increase of defect content, the lithium supplement agent of Example 2 has better improvement on the full battery charging capacity, the first cycle coulomb efficiency and the capacity retention rate after 100 cycles at 25°C.

[0151] 2) From the comparison of Example 2 and Example 3, it can be seen that Example 3 further increases the lithium vacancy defect concentration on the basis of Example 2, and introduces heterostructure doping ions to increase the defect content, thereby improving the lithium supplement ability, and at the same time, the first cycle charging capacity of the full battery, the first cycle coulomb efficiency and the capacity retention rate after 100 cycles at 25°C are all improved.

[0152] 3) From the comparison of Example 1, 4 and 5, it can be seen that as the particle size of the positive electrode lithium supplement material increases, the specific surface area also gradually decreases, and accordingly, the first cycle irreversible capacity decreases, especially when the particle size D50 of the positive electrode lithium supplement material is greater than 1.5 μm, the first cycle irreversible capacity decreases seriously, and the lithium supplement effect becomes poor; as the specific surface area decreases, the contact area between the positive electrode lithium supplement material and the air decreases, and the capacity attenuation rate can be further reduced, and the air stability of the material can be further improved. In order to make the positive electrode lithium supplement material have excellent air stability and lithium supplement effect, the particle size thereof should be 0.1 μm to 1.5 μm, and more preferably 1.5 μm.

[0153] 4) From the comparison of Example 3, 6, 7 and 8, it can be seen that on the basis of having the same degree of non-stoichiometric ratio, the use of different types of doping elements such as Co, Mg, Mo and Ni to form doping defects can make the first cycle irreversible capacity higher and the capacity attenuation rate lower, and the lithium supplement effect and air stability are good, and the first cycle charging capacity of the battery, the first cycle coulomb efficiency and the capacity retention rate after 100 cycles at 25°C are also generally excellent.

[0154] 5) From the comparison of Example 1 and Comparative Example 1, it can be seen that the use of non-stoichiometric ratio to construct defects significantly improves the first cycle irreversible capacity of the battery, improves the lithium supplement ability of the material, and further improves the first cycle charging capacity of the full battery, the first cycle coulomb efficiency and the 25°C cycle performance.

[0155] 6) From the comparison of Example 4 and Comparative Examples 2-3, it can be seen that although the manganese-based lithium supplement material of the present application has lower first cycle irreversible capacity and relatively poor lithium supplement effect compared with lithium nickelate and lithium ferrite lithium supplement materials, the capacity attenuation rate of Example 4 is significantly lower than that of Comparative Examples 2 and 3, which indicates that the air stability of the manganese-based lithium supplement material of the present application is more excellent.

[0156] 7) From the comparison of Example 1 and Comparative Example 4, Example 3 and Comparative Example 5, it can be seen that the non-stoichiometric ratio of the positive electrode lithium supplement material cannot be too large, when Li 2-x Mn 1-y M y When x in LiMn2-xO3 is greater than 0.2, the material is prone to generate spinel LiMn2O4 impurities, thereby greatly reducing the first cycle irreversible capacity, resulting in poor lithium supplement effect.

[0157] 8) From the comparison of Example 1 and Comparative Example 1, it can be seen that only by introducing heterostructure doping ions, although the lithium supplement material has excellent air stability, the first cycle irreversible capacity of the material is obviously poor, the reason is that when the lithium content in the material is sufficient, there is no lithium vacancy, the Li2MnO3 material is more prone to form ideal crystal structure, the formation energy barrier of defect structure is increased, resulting in that even if the doping ions are introduced, it is also difficult to construct defects.

[0158] Finally, it should be pointed out that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A cathode lithium supplementation material, wherein, The positive electrode lithium replenishment material is a non-stoichiometric compound, and the chemical composition of the positive electrode lithium replenishment material is Li. 2-x Mn 1-y M y O3, where M is a dopant element, 0 < x ≤ 0.2, 0 ≤ y ≤ 0.2; The valence state of M is not +4, or the pure-phase lithium oxide of M is isomerized with the layered Li2MnO3 material.

2. The positive electrode lithium replenishment material according to claim 1, wherein, M includes one or more of Mg, Al, Ti, V, Cr, Fe, Co, Ni, Zn, Sr, Y, Zr, Nb, Mo, and W.

3. The positive electrode lithium replenishment material according to claim 1 or 2, wherein, The positive electrode lithium replenishment material is a primary particle.

4. The cathode lithium replenishment material according to any one of claims 1-3, wherein, The D50 particle size of the positive electrode lithium replenishment material is 0.1μm to 2μm.

5. The positive electrode lithium replenishment material according to any one of claims 1-4, wherein, The specific surface area of ​​the cathode lithium replenishment material is 0.5 m². 2 / g~24m 2 / g.

6. A method for preparing the positive electrode lithium replenishment material according to any one of claims 1-5, wherein, The preparation method includes the following steps: 1) The manganese source, lithium source, and compound containing doped element M are mixed according to the designed ratio to obtain a mixture; 2) The mixture is sintered to obtain the positive electrode lithium replenishment material.

7. The preparation method according to claim 6, wherein, The mixing process is carried out under solid-phase conditions.

8. The preparation method according to claim 6 or 7, wherein, The sintering process includes a first sintering and a second sintering performed sequentially. The temperature of the first sintering is 450-600℃, and the sintering time is 4-8h; The secondary sintering temperature is 750–950℃, and the sintering time is 6–12 hours.

9. A positive electrode sheet, comprising a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein, The positive electrode active material layer includes the positive electrode lithium replenishment material according to any one of claims 1-5.

10. A lithium-ion battery comprising the positive electrode sheet as described in claim 9.

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