Modified lithium-ion cathode material, method for manufacturing the same, and lithium-ion battery

Abstract

The present application relates to modified lithium ion positive electrode material and its manufacturing method, and lithium ion battery. A modified lithium ion positive electrode material is provided, which comprises a positive electrode material body and a surface coating layer, wherein the chemical composition of the surface coating layer is high-entropy solid-state electrolyte Li7La3(M x M1 a M2 b M3 c …Mi j )2O 12 , wherein M is Zr or Ti, and x>0; M1, M2, M3…Mi are elements other than Li, La, Zr and Ti, i is a positive integer and 5≤i≤10, a, b, c…j are stoichiometric coefficients of each element, a, b, c…j≥0, and x+a+b+c+…+j=1. The present application further improves the ion conductivity at the interface by high-entropy of the solid-state electrolyte, and further reduces the problem of energy density reduction caused by surface coating by lithium enrichment.

Description

TECHNICAL FIELD

[0001] The present application relates to a coated modified positive electrode material, belonging to the technical field of lithium ion batteries. Specifically, the present application relates to a modified lithium ion positive electrode material, a manufacturing method thereof, and a lithium ion battery using the modified lithium ion positive electrode material. BACKGROUND

[0002] As a new type of energy storage device, lithium ion batteries have the advantages of high voltage, low self-discharge rate, high energy density, etc., and are widely used in electronic products, vehicles, energy storage, etc. However, as the energy density of lithium ion batteries becomes higher and higher, the improvement of their safety performance has become the primary concern of researchers. Currently, large-scale commercial lithium ion batteries mainly use liquid electrolyte, which is flammable and easy to leak, and has a high safety risk.

[0003] In order to solve the above problems, researchers have proposed a method of surface coating to modify ternary positive electrode materials, which mainly includes inhibiting side reactions on the surface of the positive electrode material, improving electron and ion conduction, and promoting interface ion charge transfer. However, conventional oxides and fluorides as coating materials themselves have no electrochemical activity and poor ion conductivity, which will lead to increased impedance and decreased rate performance of the material.

[0004] In recent years, high-entropy oxides as coating materials have been increasingly concerned in the modification of lithium ion battery positive electrode materials. High-entropy oxides are a class of multi-component materials composed of five or more metal cations with equal or nearly equal amounts of substances, which have a single solid solution structure. In a highly disordered multi-component system, high entropy produces some properties with good application prospects, such as high-entropy effect, severe lattice distortion, slow diffusion, and cocktail effect. High entropy is beneficial to alleviate the disadvantage of uncontrolled lattice oxygen redox activity, and helps to further improve the cycle stability of the material. It has been reported that the use of some high-entropy oxides for surface coating modification of positive electrode materials can avoid or reduce direct contact between the positive electrode material and the electrolyte, alleviate the capacity decay caused by interface side reactions, and protect the stability of the material. SUMMARY

[0005] Problems to be solved by the application

[0006] However, in the prior art, there is still the problem of energy density reduction caused by the coating of high-entropy oxide layer, and the high-entropy oxide has a disordered structure, low ion conductivity and unstable structure, which is prone to oxygen loss and metal dissolution.

[0007] To solve the problems in the prior art, the present application aims to provide a multifunctional high-entropy solid-state electrolyte-coated modified positive electrode material and a preparation method and application thereof, which, while maintaining the effects of mitigating surface side reactions and enhancing ion transmission in the existing high-entropy oxide coating technology, further improves the ion conductivity at the interface through high-entropy solid-state electrolyte and further reduces the problem of energy density reduction caused by surface coating through lithium enrichment.

[0008] Solution for solving the problem

[0009] To achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0010] One aspect of the present application provides a modified lithium ion positive electrode material, comprising a positive electrode material body and a surface coating layer,

[0011] The chemical composition of the surface coating layer is a high-entropy solid-state electrolyte Li7La3(M x M1 a M2 b M3 c …Mi j )2O 12 , wherein M is Zr or Ti, and x>0; M1, M2, M3…Mi are elements other than Li, La, Zr and Ti, i is a positive integer and 5≤i≤10, a, b, c…j are stoichiometric coefficients of each element, a, b, c…j≥0, and x+a+b+c+…+j=1.

[0012] Further, according to the modified lithium ion positive electrode material described above, the modified lithium ion positive electrode material further comprises a shallow surface doping layer, the shallow surface doping layer is arranged between the positive electrode material body and the surface coating layer, and the metal elements in the shallow surface doping layer include all the metal elements in the positive electrode material body and at least one metal element in the surface coating layer.

[0013] Preferably, the average thickness of the shallow surface doping layer is 5-100 nm, preferably 5-50 nm.

[0014] Preferably, the average thickness of the surface coating layer is 2 nm-5 μm, preferably 5 nm-0.5 μm.

[0015] Further, according to the modified lithium ion positive electrode material described above, M1, M2, M3…Mi are at least one selected from Mg, B, Ca, Sc, Ti, V, Cr, Te, Fe, Cu, Zn, Ga, Ge, Sr, Y, Nb, Mo, Ru, Sn, Sb and W,

[0016] Preferably, b=c=…=j, and

[0017] wherein in the high-entropy solid-state electrolyte, the molar ratio of La relative to M, M1, M2, …, Mi is La:(M:M1:M2:…:Mi) = 3:2(0.5-0.8:0.1:0.1:…:0.1);

[0018] Preferably, i = 5, M is Zr, and M1, M2, M3, M4 and M5 are Al, Ca, Cr, Mg and Zn, respectively;

[0019] Preferably, the high-entropy solid-state electrolyte is Li7La3(Zr 0.5 Al 0.1 Ca 0.1 Cr 0.1 Mg 0.1 Zn 0.1 )2O 12 .

[0020] Further, according to the modified lithium-ion positive electrode material described above, wherein the positive electrode material body comprises a ternary positive electrode material, the ternary positive electrode material comprises at least one of a nickel-cobalt-manganese ternary positive electrode material and a nickel-cobalt-aluminum ternary positive electrode material;

[0021] Preferably, the high-entropy solid-state electrolyte is a lithium-rich high-entropy solid-state electrolyte;

[0022] Preferably, the mass ratio of the surface coating layer relative to the positive electrode material body is 0.1%-10%, preferably 1%-5%;

[0023] Preferably, the average particle size of the modified lithium-ion positive electrode material is 5-15 μm, preferably 5-10 μm.

[0024] Another aspect of the present application provides a manufacturing method of the modified lithium-ion positive electrode material described above, comprising the following steps:

[0025] S1: respectively preparing a raw salt solution A of a positive electrode material body, a raw salt solution B of a high-entropy solid-state electrolyte, a precipitant solution C and a complexing agent solution D;

[0026] S2: co-precipitation reaction of the raw salt solution A, the precipitant solution C and the complexing agent solution D to obtain a precursor I;

[0027] S3: further introducing the raw salt solution B, the precipitant solution C and the complexing agent solution D into the precursor I for co-precipitation reaction to obtain a precursor II; and

[0028] S4: calcining the precursor II to obtain the modified lithium-ion positive electrode material.

[0029] Further, according to the above-mentioned method for manufacturing modified lithium ion positive electrode material, wherein the step S3 is performed in two steps: sub-step S3-1, further introducing the raw salt solution A, the raw salt solution B, the precipitant solution C and the complexing agent solution D into the precursor I to perform a co-precipitation reaction to obtain an intermediate precursor; and sub-step S3-2, further introducing the raw salt solution B, the precipitant solution C and the complexing agent solution D into the intermediate precursor to perform a co-precipitation reaction to obtain the precursor II.

[0030] Further, according to the above-mentioned method for manufacturing modified lithium ion positive electrode material, wherein the raw salt solution A is prepared using at least one of sulfate, nitrate and chloride of nickel, cobalt, manganese or aluminum, preferably the total concentration of nickel, cobalt, manganese or aluminum metal ions is 1-5 mol / L;

[0031] Preferably, the raw salt solution B is prepared using at least one of sulfate, nitrate and chloride of M1, M2, M3…Mi, preferably the total concentration of M1, M2, M3…Mi ions is 1-5 mol / L;

[0032] Preferably, the precipitant solution C is prepared using at least one of sodium hydroxide and sodium carbonate, preferably the concentration is 3-5 mol / L; and

[0033] The complexing agent solution D is an ammonia solution with a concentration of 0.5-3 mol / L.

[0034] Further, according to the above-mentioned method for manufacturing modified lithium ion positive electrode material, wherein in the step S2 and the step S3, the reaction temperature is 45-65℃, preferably 50-60℃, the reaction atmosphere is an inert gas atmosphere, preferably a nitrogen atmosphere, the pH value of the reaction system is 10.5-13.5, and

[0035] The co-precipitation reaction is performed under stirring at a stirring speed of 50-500 rpm;

[0036] Preferably, in the step S4, aging and drying are further performed before calcination, and cooling is further performed after calcination.

[0037] Preferably, after aging, the precursor II is repeatedly filtered or stirred with deionized water until the pH value of the supernatant shows neutrality.

[0038] Preferably, in the step S4, the aging temperature is 30-70℃, and the aging time is 5-15 h; and

[0039] The drying temperature is 65-115℃, and the drying time is 6-12 h.

[0040] Further, according to the method for manufacturing the modified lithium ion cathode material, in the step S4, the precursor II and the lithium source in a stoichiometric ratio are weighed, and after being uniformly mixed by ball milling, two-stage high-temperature calcination is performed.

[0041] Preferably, the stoichiometric ratio of the lithium source to the precursor II in terms of metal ion moles is 1.1-1.5.

[0042] Preferably, the lithium source is at least one selected from Li2CO3, LiOH, and LiAc, and

[0043] In the two-stage high-temperature calcination, the sintering temperature of the first stage is 350-650 DEG C, and the holding time is 1-8 h; the sintering temperature of the second stage is 650-950 DEG C, and the holding time is 6-20 h.

[0044] Another aspect of the present application provides a lithium ion battery, comprising a cathode and an anode, wherein the cathode comprises the modified lithium ion cathode material according to the above or obtained by the method according to the above.

[0045] Effects of the application

[0046] The technical scheme provided by the present application has the following beneficial effects:

[0047] 1. The surface coating layer can provide good surface protection, and as a physical barrier, it can significantly reduce surface side reactions and improve cycle performance.

[0048] 2. The surface coating layer can enhance the ionic conductivity at the interface and improve the rate performance.

[0049] 3. The preferred co-precipitation in-situ coating method can achieve a uniform and controllable coating effect in terms of thickness and coating composition, enhance the integrity of the surface coating layer, and improve the cycle performance of the material.

[0050] 4. In the lithium-rich high-entropy solid-state electrolyte, the lithium-excess state directly sintered high-entropy solid-state electrolyte coated modified cathode material can utilize the fluxing effect of lithium salt to reduce the sintering temperature of the solid-state electrolyte, adapt the sintering temperature of the solid-state electrolyte to the cathode material, achieve the effect of simultaneous sintering of the cathode material and the solid-state electrolyte coating layer and better crystallinity of the solid-state electrolyte, and enhance the bonding effect of the core and the coating layer; the reduced sintering temperature prevents lithium vacancies and lithium-nickel mixing caused by excessive temperature; on the other hand, the excess lithium source can achieve the effect of lithium supplementation, especially in the silicon-based system, which can improve the initial efficiency and cycle performance and compensate for the defect of energy density reduction caused by common coating.

[0051] 5、The preferred high-entropy material coating and surface phase doping of the application can improve the thermal stability of the positive electrode material, especially the high-nickel positive electrode material, enhance the bond energy of the TM-O bond between transition metals and oxygen, reduce oxygen loss, and reduce the risk of thermal runaway.

[0052] 6、The preferred high-entropy material coating and doping of the application can improve the hardness of the outer layer, modify the particle hardness of the lithium ion positive electrode material to be no less than 150MPa, effectively improve the mechanical strength and stability of the single particle of the positive electrode material, and effectively reduce the lithium-nickel mixing of the positive electrode material and improve the cycle performance.

[0053] 7、The conventional method of coating high-entropy material on the surface of the positive electrode material and then sintering will form a gradient distribution of elements in the penetration layer, while the preferred homogeneous high-entropy surface phase doping layer formed in situ in the application can control the existence of high-valence transition metals, so that the oxygen defects generated in the cycle process of the material are trapped around these doping atoms, forming a "pinning effect", thereby hindering the further aggregation of these defects to generate dislocations or cracks, and significantly improving the structural stability of the material in the cycle process. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 The schematic diagram of the modified lithium ion positive electrode material, wherein the positive electrode material body is a nickel-cobalt-manganese ternary positive electrode material, the surface doping layer is a mixture of the nickel-cobalt-manganese ternary positive electrode material and the high-entropy solid-state electrolyte, and the surface coating layer is a high-entropy solid-state electrolyte layer. DETAILED DESCRIPTION

[0055] Various exemplary embodiments, features, and aspects of the present application will be described in detail below. The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations.

[0056] In addition, in order to better illustrate the present application, numerous specific details are given in the following detailed description. Those skilled in the art should understand that the present application can also be implemented without certain specific details. In some other examples, methods, means, apparatus and steps that are well known to those skilled in the art are not described in detail, in order to highlight the main idea of the present application.

[0057] Unless otherwise stated, the units used in the specification are international standard units, and the numerical values and numerical ranges appearing in the present application should be understood to include the systematic errors that are inevitable in industrial production.

[0058] In this specification, the meaning of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0059] In this specification, reference to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc. means that a particular feature (e.g. a characteristic, structure, property, and / or characteristic) described is included in at least one embodiment described herein, and can or can not be present in other embodiments. In addition, it is to be understood that the described features can be combined in various embodiments in any suitable manner.

[0060] In this specification, a numerical range represented by "numerical value A to numerical value B" means a range including the end point numerical values A, B.

[0061] <First aspect>

[0062] The first aspect of the present application provides a modified lithium-ion cathode material, comprising a cathode material body and a surface coating layer, wherein the chemical composition of the surface coating layer is high-entropy solid-state electrolyte Li7La3(M x M1 a M2 b M3 c …Mi j )2O 12 , wherein M is Zr or Ti, and x>0; M1, M2, M3…Mi are elements other than Li, La, Zr and Ti, i is a positive integer and 5≤i≤10, a, b, c…j are stoichiometric coefficients of each element, a, b, c…j≥0, and x+a+b+c+…+j=1.

[0063] The modified lithium-ion cathode material of the present application has a surface coating layer with a specific structure, and the high-entropy oxide solid-state electrolyte forms a coating with uniform and controllable thickness and coating composition on the surface of the cathode material body, enhances the integrity of the coating layer, and does not hinder the conduction of ions during battery cycling, but also maintains the stability of the cathode material, thereby improving the cycling performance of the material.

[0064] In addition, the high-entropy oxide solid-state electrolyte as a physical barrier with high hardness of the cathode material body also provides surface protection for the cathode material, significantly reduces the occurrence of surface side reactions, and improves the cycling performance. Further, the surface coating layer contains high-entropy oxide solid-state electrolyte, which enhances the ionic conductivity at the interface and improves the rate performance.

[0065] In an embodiment of the present application, the modified lithium-ion positive electrode material further comprises a shallow doping layer, the shallow doping layer is arranged between the positive electrode material body and the surface coating layer, and the metal elements in the shallow doping layer comprise all the metal elements in the positive electrode material body and at least one metal element in the surface coating layer. Optionally, the shallow doping layer can further comprise other elements except the coating layer. In a specific embodiment of the present application, the shallow doping layer is formed by mixing the high-entropy solid-state electrolyte with the positive electrode material body, and the average thickness of the shallow doping layer is 5-100 nm, preferably 5-50 nm, and more preferably 10-30 nm.

[0066] In an embodiment of the present application, the positive electrode material body comprises a ternary positive electrode material, more specifically at least one of a nickel-cobalt-manganese ternary positive electrode material and a nickel-cobalt-aluminum ternary positive electrode material.

[0067] In a specific embodiment of the present application, the elements of the shallow doping layer comprise transition metal elements contained in the positive electrode material and elements contained in the high-entropy solid-state electrolyte coating layer material, more specifically all the metal elements in the positive electrode material body and part of the metal elements in the surface coating layer and other elements except the coating layer. The structure type of the shallow doping layer is a homogeneous highly disordered multi-component system formed by the coprecipitation reaction of the salt solution in the nickel-cobalt-manganese or nickel-cobalt-aluminum ternary positive electrode material and the salt solution for generating the high-entropy oxide solid-state electrolyte, the high-entropy doping disordered system is introduced into the layered structure of the ternary material to form a "pinning effect", stabilize the multi-electron reaction, inhibit the oxygen loss, dislocation generation and harmful phase change, promote the rapid diffusion of lithium ions, and stabilize the surface structure, enhance the thermodynamic stability of the material, and improve the mechanical properties and cycle stability of the material.

[0068] It should be noted that "homogeneous" in the structure type of the shallow doping layer means that the elements in the shallow doping layer are uniformly distributed in the layer without concentration gradient.

[0069] In an embodiment of the present application, the average thickness of the surface coating layer is 2 nm-5 μm, preferably 5 nm-0.5 μm. If the surface coating layer is too thick, it will prolong the transmission path of lithium ions, resulting in the decline of charge transport performance and the loss of specific capacity. If it is too thin, it will result in that the performance improvement of the material is not obvious.

[0070] The modified lithium ion positive electrode material has a specific structure, a shallow surface doping layer with a certain thickness, and a surface coating layer. On the one hand, the thermal stability of the positive electrode material, especially the high-nickel positive electrode material, is improved, the bond energy of the TM-O bond formed between the transition metal and oxygen is enhanced, the oxygen loss is reduced, and the risk of thermal runaway is reduced. On the other hand, the hardness of the outer layer of the positive electrode material body is improved, so that the particle hardness of the ternary positive electrode material is not less than 150 MPa, effectively improving the mechanical strength and stability of the single particle of the ternary positive electrode material, and at the same time, the lithium-nickel mixing in the ternary positive electrode material can be effectively reduced, and the cycle performance is improved.

[0071] In an embodiment of the present application, M1, M2, M3,..., Mi are at least one selected from Mg, B, Ca, Sc, Ti, V, Cr, Te, Fe, Cu, Zn, Ga, Ge, Sr, Y, Nb, Mo, Ru, Sn, Sb, W. Preferably, b=c=...=j, and in the high-entropy solid-state electrolyte, the molar ratio of La to M, M1, M2,..., Mi is La:(M:M1:M2:...:Mi)=3:2(0.5-0.8:0.1:0.1:...:0.1).

[0072] In an embodiment of the present application, the mass ratio of the surface coating layer to the positive electrode material body is 0.1%-10%, preferably 1%-5%. If the surface coating layer is too much, the cycle performance and rate performance cannot be further improved, which is economically disadvantageous; if it is too little, a uniform coating cannot be formed, and the protective effect and hardness improvement effect of the relatively hard surface coating layer on the body material cannot be exerted.

[0073] In an embodiment of the present application, the average particle size D50 of the modified lithium ion positive electrode material is 5-15 μm, preferably 5-10 μm. For example, the average particle size D50 of the modified lithium ion positive electrode material can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc.

[0074] In a specific embodiment of the present application, the high-entropy solid-state electrolyte is a lithium-rich high-entropy solid-state electrolyte. In a preferred embodiment of the present application, i=5, M is Zr, x=0.5, and M1, M2, M3, M4, and M5 are Al, Ca, Cr, Mg, and Zn, respectively; more specifically, Li7La3(Zr 0.5 Al 0.1 Ca 0.1 Cr 0.1 Mg 0.1 Zn 0.1 )2O 12In addition to La and Zr, five other metal elements are also included. The atomic sizes of the five elements of Al, Ca, Cr, Mg and Zn are close, can form a homogeneous mixed phase, easily realize a stable high-entropy structure, and can produce a large mixed entropy value, which is helpful to the formation of a solid solution structure, and therefore the combination of these elements is preferred as the high-entropy solid electrolyte of the present application.

[0075] Figure 1 A schematic diagram of a lithium ion battery positive electrode material in-situ doped with a high-entropy solid electrolyte and co-modified. Specifically, as shown in Figure 1 the modified lithium ion positive electrode material of the present application comprises a body of a nickel-cobalt-manganese ternary positive electrode material, a shallow surface doping layer and a surface coating layer, the shallow surface doping layer is a mixture of the nickel-cobalt-manganese ternary positive electrode material and the high-entropy solid electrolyte, and the surface coating layer is a high-entropy solid electrolyte layer, and the high-entropy solid electrolyte can specifically be Li7La3(Zr 0.5 Al 0.1 Ca 0.1 Cr 0.1 Mg 0.1 Zn 0.1 )2O 12 .

[0076] <Second aspect>

[0077] The second aspect of the present application provides a manufacturing method of a modified lithium ion positive electrode material, which comprises the following steps:

[0078] S1: preparing raw salt solutions A of a positive electrode material body, B of a high-entropy solid electrolyte, C of a precipitant and D of a complexing agent, respectively;

[0079] S2: performing a co-precipitation reaction on the raw salt solution A, the precipitant solution C and the complexing agent solution D to obtain a precursor I;

[0080] S3: further introducing the raw salt solution B, the precipitant solution C and the complexing agent solution D into the precursor I to perform a co-precipitation reaction to obtain a precursor II; and

[0081] S4: calcining the precursor II to obtain the modified lithium ion positive electrode material.

[0082] The manufacturing method of the modified lithium ion positive electrode material of the present application can realize a coating effect with controllable thickness and coating composition by in-situ coating through co-precipitation, so as to fully play the role of the surface coating layer of the high-entropy solid electrolyte, and improve the cycle performance and rate performance.

[0083] The solvent used is not particularly limited, as long as it can dissolve the raw materials of the positive electrode material body and the raw materials for forming the high-entropy solid electrolyte. For example, water can be used.

[0084] In an embodiment of the present application, step S3 is performed in two steps: sub-step S3-1, further feeding raw salt solution A, raw salt solution B, precipitant solution C and complexing agent solution D into precursor I to perform co-precipitation reaction to obtain intermediate precursor; and sub-step S3-2, further feeding raw salt solution B, precipitant solution C and complexing agent solution D into the intermediate precursor to perform co-precipitation reaction to obtain precursor II.

[0085] By performing selective pumping of different element mixed salt solution in sub-step S3-1, part of the composition elements can be mixed into the shallow doping layer. Moreover, since the different element mixed salt solution is selectively pumped by co-precipitation, the metal elements are homogeneously distributed in the shallow penetration layer. Preferably, by pumping all the composition elements of the high-entropy solid-state electrolyte into the reaction container in sub-step S3-1 and performing sufficient reaction, a structure in which the composition elements of the positive electrode material body and all the composition elements of the high-entropy solid-state electrolyte coating layer material are mixed in the shallow doping layer is formed. Therefore, in the shallow doping layer, the composition elements of the high-entropy solid-state electrolyte material occupy the octahedral or tetrahedral sites in the transition metal layer or lithium ion layer in the positive electrode material body structure, forming a derived structure containing one or several structures of layered structure, spinel structure, rock salt structure or disordered structure.

[0086] In an embodiment of the present application, raw salt solution A for the positive electrode material body is prepared using at least one of sulfate, nitrate and chloride salt of nickel, cobalt, manganese or aluminum, and preferably the total concentration of nickel, cobalt, manganese or aluminum metal ions is 1-5 mol / L. Preferably, the raw salt solution A is prepared by selecting salts with the same counter ion.

[0087] In an embodiment of the present application, raw salt solution B for forming high-entropy solid-state electrolyte is prepared using at least one of sulfate, nitrate and chloride salt of M1, M2, M3……Mi, and preferably the total concentration of M1, M2, M3……Mi ions is 1-5 mol / L. Preferably, the raw salt solution B is prepared by selecting salts with the same counter ion.

[0088] In an embodiment of the present application, precipitant solution C is prepared using at least one of sodium hydroxide and sodium carbonate, and preferably the concentration is 3-5 mol / L; and complexing agent solution D is ammonia solution with a concentration of 0.5-3 mol / L.

[0089] In an embodiment of the present application, in steps S2 and S3, the reaction temperature is 45-65°C, preferably 50-60°C, the reaction atmosphere is an inert gas atmosphere, preferably a nitrogen atmosphere, the pH value of the reaction system is 10.5-13.5, and the co-precipitation reaction is carried out under stirring at a stirring speed of 50-500 rpm, preferably 200-500 rpm. By keeping the pH value of the reaction system alkaline, the co-precipitation reaction can be carried out smoothly.

[0090] In an embodiment of the present application, in step S4, aging and drying are further carried out before calcination, and cooling is further carried out after calcination. After aging, the precursor II is repeatedly filtered or washed by stirring with deionized water until the pH value of the supernatant shows neutrality.

[0091] In an embodiment of the present application, in step S4, the aging temperature is 30-70°C, and the aging time is 5-15 h; and the drying temperature is 65-115°C, and the drying time is 6-12 h.

[0092] In an embodiment of the present application, in step S4, the precursor II and the lithium source in a relative excess are weighed according to the stoichiometric ratio, uniformly ball-milled, and then subjected to two-stage high-temperature calcination. In a preferred embodiment of the present application, the stoichiometric ratio of the lithium source to the precursor II in terms of metal ion moles is 1.1-1.5. By directly sintering the high-entropy solid-state electrolyte-coated modified positive electrode material in a lithium-excess state, on the one hand, the sintering temperature of the solid-state electrolyte can be reduced by taking advantage of the fluxing effect of the lithium salt, and on the other hand, the excess lithium source can achieve a lithium supplement effect, especially in a silicon-based system, which can improve the initial efficiency and cycle performance and make up for the defect of energy density reduction caused by common coating.

[0093] In an embodiment of the present application, the lithium source is at least one selected from Li2CO3, LiOH, and LiAc. In an embodiment of the present application, in the two-stage high-temperature calcination, the sintering temperature of the first stage is 350-650°C, and the holding time is 1-8 h; the sintering temperature of the second stage is 650-950°C, and the holding time is 6-20 h. In addition, the sintering atmosphere is not particularly limited. The sintering can be carried out in an air, oxygen, or air atmosphere with an adjusted oxygen partial pressure.

[0094] Through the first low-temperature sintering, the components in the material are uniformly distributed, the pores and defects in the material are eliminated, the lithium carbonate is decomposed into oxides, the exhaust gas is discharged, the material density and the integrity of the crystal structure are improved, and the grain size of the material is gradually reduced, and the crystallinity is preliminarily improved; through the second high-temperature sintering at a higher temperature, the grain size of the material is further reduced, and the crystal structure and mechanical strength of the material are greatly improved, achieving excellent electrochemical performance.

[0095] In the specific embodiment of the present application, a preparation method of a multifunctional high-entropy solid-state electrolyte coated ternary positive electrode material is provided, and the preparation steps are as follows: a salt solution and a complexing agent solution, a precipitant solution are respectively introduced into a reaction kettle, and after stirring at a certain temperature for a period of time, aging is carried out, and after aging, washing and drying are carried out, the dried precursor is mixed with a lithium source, and high-temperature sintering is carried out to obtain a high-entropy oxide solid-state electrolyte coated ternary material. The preparation process includes the following steps:

[0096] (1) A mixed salt solution A of nickel, cobalt and manganese is prepared according to the stoichiometric ratio, preferably, the nickel salt, cobalt salt and manganese salt or aluminum salt are at least one of sulfate, nitrate and chloride, and further preferably, the total concentration of nickel, cobalt and manganese metal ions in the mixed salt solution A is 1-5 mol / L;

[0097] A soluble La salt, a Zr salt, a M1 salt, a M2 salt, … a Mi salt are dissolved in deionized water to obtain a mixed salt solution B according to the stoichiometric ratio, preferably, La, Zr, M1, M2, … Mi can form a high-entropy oxide solid-state electrolyte of garnet-type oxide, and further preferably, the total concentration of metal ions in the mixed salt solution B is 1-5 mol / L;

[0098] A precipitant solution C is prepared, preferably, the precipitant includes at least one of sodium hydroxide and sodium carbonate, and the concentration is 3-5 mol / L;

[0099] A complexing agent solution D is prepared, preferably, the complexing agent is ammonia water, and the concentration is 0.5-3 mol / L;

[0100] (2) The mixed salt solution A, the precipitant solution C and the complexing agent solution D are introduced into the reaction kettle to carry out a co-precipitation reaction to obtain a precursor I;

[0101] (3) The mixed salt solutions A and B, the precipitant solution C and the complexing agent solution D are introduced into the reaction kettle to carry out a co-precipitation reaction to obtain a precursor II;

[0102] (4) The mixed salt solution B, the precipitant solution C and the complexing agent solution D are introduced into the reaction kettle to carry out a co-precipitation reaction to obtain a precursor III;

[0103] (5) The mixed solution after the reaction in step (3) is aged, preferably, the aging temperature is 30-70℃, and the aging time is 5-15h;

[0104] (6) The mixed solution after aging in step (4) is washed with deionized water until the pH value of the supernatant shows neutral, preferably, repeated filtration or stirring washing with deionized water is adopted;

[0105] (7) drying the material after washing in step (5), preferably, the drying temperature is 65-115℃, the drying time is 6-12h, to obtain the coated ternary material precursor;

[0106] (8) taking the coated precursor and the relative excess lithium source according to the stoichiometric ratio, preferably, the lithium source is at least one of Li2CO3, LiOH, LiAc, ball-milling uniformly, and then performing two-stage high-temperature calcination under the gas atmosphere of air or oxygen, and naturally cooling to obtain the high-entropy solid electrolyte layer coated and superficially doped ternary material.

[0107] Preferably, the mixed salt solution B in step (1) has multiple different element mixing formulas, and is prepared at the same time and placed in at least two tanks, respectively, and is divided into B, B1, B2...Bi.

[0108] Preferably, the temperature of the co-precipitation reaction in steps (2), (3) and (4) is 45-65℃, the reaction atmosphere is nitrogen atmosphere or other inert gas atmosphere, and the pH value of the reaction system is 10.5-13.5.

[0109] Preferably, the reaction temperature in steps (2), (3) and (4) is 30-60℃; the stirring paddle in the reaction kettle is kept stirring during the process of introducing the salt solution, and the stirring rate is 50-500rpm.

[0110] Preferably, the sintering process in step (8) is divided into two stages, the sintering temperature of the first stage is 350-650℃, and the holding time is 1-8h; the sintering temperature of the second stage is 650-950℃, and the holding time is 6-20h.

[0111] <Third aspect>

[0112] The third aspect of the present application provides a lithium ion battery comprising the modified lithium ion cathode material as described above or the modified lithium ion cathode material obtained by the manufacturing method as described above.

[0113] The modified lithium ion cathode material of the present application can significantly reduce the interface side reaction, improve the mechanical strength and stability of the ternary cathode material particles, enhance the ion conductivity at the interface and improve the rate performance due to the uniformity and hardness and strength of the surface coating layer, and therefore the lithium ion battery using the modified lithium ion cathode material of the present application can ensure excellent battery performance and good safety performance.

[0114] The lithium ion battery of the present application comprises necessary components such as positive electrode sheet, negative electrode sheet and electrolyte, and of course also comprises other necessary or auxiliary components.

[0115] Examples

[0116] The embodiments of the present application will be described in detail below with reference to Examples, but those skilled in the art will understand that the following Examples are only for illustrating the present application and should not be considered as limiting the scope of the present application. The specific conditions not mentioned in the Examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be obtained commercially.

[0117] Example 1

[0118] The present embodiment provides a preparation method of in-situ high-entropy solid-state electrolyte doped coated co-modified lithium ion battery positive electrode material, comprising the following steps:

[0119] (1) Dissolve nickel sulfate, cobalt sulfate and manganese sulfate in water to obtain a mixed salt solution A of nickel, cobalt and manganese; wherein the total molar concentration of the three elements of nickel, cobalt and manganese is 2 mol / L, and the molar ratio of nickel, cobalt and manganese is 0.8:0.1:0.1; a mixed solution B of metal nitrate is prepared, wherein the molar ratio of zirconium nitrate, aluminum nitrate, calcium nitrate, chromium nitrate, magnesium nitrate and zinc nitrate is 5:1:1:1:1:1, and the total molar concentration of metal elements of lanthanum, zirconium, aluminum, calcium, chromium, magnesium and zinc is 3 mol / L; a sodium hydroxide solution C with a concentration of 3 mol / L is prepared as a precipitant. An ammonia solution with a concentration of 3 mol / L is prepared as a complexing agent.

[0120] (2) Pump solutions A, C and D into the reaction kettle at the same time, the stirring rate of the stirring paddle in the reaction kettle is 500 rpm, the reaction temperature is 55°C, when the particle size of the precipitate reaches 10 μm, stop feeding, and record the amount of mixed salt introduced.

[0121] (3) Pump solutions A, B, C and D into the reaction kettle at the same time, the stirring rate of the stirring paddle in the reaction kettle is 500 rpm, the reaction temperature is 55°C, when the mass of solute in the metal salt of mixed solution B is 0.5% of the mass of the solute in solution A in step 2 and the mass of the solute in solution A in step 3 added at the same time as solution B, stop feeding.

[0122] (4) Pump solutions B, C and D into the reaction kettle at the same time, the stirring rate of the stirring paddle in the reaction kettle is 500 rpm, the reaction temperature is 55°C, when the mass of solute in the metal salt of mixed solution B is 1% of the mass of the solute in step 3, stop feeding.

[0123] (5) The mixed solution after reaction in the above (4) is aged at 55°C for 12 h.

[0124] (6) The mixed solution after aging in the above (5) is repeatedly filtered and washed with 50°C deionized water until the pH value of the supernatant shows neutral.

[0125] (7) The filter cake after washing in the above (6) is placed in a blast drying oven, and dried at 110°C for 8h to obtain a ternary material precursor coated with high-entropy lanthanum zirconate hydroxide in situ.

[0126] (8) The precursor obtained in the above (7) and lithium carbonate in an excess of 1.2 times the stoichiometric ratio are weighed and mixed uniformly by ball milling, and the mixture is placed in a mullite crucible and calcined at 550°C for 6h, and then calcined at 900°C for 10h, and then naturally cooled to obtain Li7La3(Zr 0.5 Al 0.1 Ca 0.1 Cr 0.1 Mg 0.1 Zn 0.1 )2O 12 and a surface-doped modified lithium-rich ternary positive electrode material, wherein the average particle size of the modified lithium ion positive electrode material is 11μm, the average thickness of the surface coating layer is 50nm, the mass ratio of the surface coating layer to the positive electrode material body is 2%, and the average thickness of the surface-doped layer is 30nm.

[0127] Example 2

[0128] Except that the zirconium nitrate in the mixed solution B is replaced by titanium nitrate, the rest is the same as example 1.

[0129] Example 3

[0130] Except that the reaction time in step (3) is changed to make the average thickness of the surface-doped layer 5nm, the rest is the same as example 1.

[0131] Example 4

[0132] Except that the reaction time in step (3) is changed to make the average thickness of the surface-doped layer 50nm, the rest is the same as example 1.

[0133] Example 5

[0134] Except that the reaction time in step (4) is changed to make the average thickness of the surface coating layer 5nm, the rest is the same as example 1.

[0135] Example 6

[0136] Except that the reaction time in step (4) is changed to make the average thickness of the surface coating layer 0.5μm, the rest is the same as example 1.

[0137] Example 7

[0138] Except that the operation of step (3) is not performed, and no surface-doped layer is set, the rest is the same as example 1.

[0139] Example 8

[0140] Except that 1.2 times excess lithium carbonate in step (8) is replaced by 1.0 times, and the high-entropy solid-state electrolyte is not lithium-rich, the rest is the same as example 1.

[0141] Comparative example 1

[0142] Except that steps (3) and (4) are not performed, the rest is the same as example 1. As can be seen from table 1 below, the positive electrode material of comparative example 1 is not coated and doped with high-entropy solid-state electrolyte, and its cycle performance and material thermal stability are poor.

[0143] Comparative example 2

[0144] Except that zirconium nitrate and lanthanum nitrate in mixed solution B are removed, and step (3) is not performed, the rest is the same as example 1, to obtain a lithium ion battery positive electrode material coated and modified with high-entropy oxide Li(Al 0.2 Ca 0.2 Cr 0.2 Mg 0.2 Zn 0.2 )O2.

[0145] Using a button cell test system, the modified lithium ion positive electrode material obtained in the above examples and comparative examples is applied to a button cell and subjected to charge-discharge test at room temperature (25℃), and the discharge rate is 0.1C, the voltage range is 2.75-4.25, the initial efficiency of the button cell is recorded, and the capacity retention rate after 100 cycles is recorded, and the decomposition temperature of the material is tested by DSC.

[0146] Table 1

[0147] Initial efficiency (%) Capacity retention rate (%) Thermal decomposition temperature (°C) Example 1 90.8 91.4 230 Example 2 89.9 91.5 228 Example 3 88.7 90.8 225 Example 4 87.9 89.3 232 Example 5 89.2 89.8 224 Example 6 85.4 86.6 234 Example 7 89.3 86.4 217 Example 8 83.7 84.5 227 Comparative Example 1 88.6 82.1 210 Comparative Example 2 88.9 84.2 212

[0148] The test results show that the modified lithium ion positive electrode material of the present application significantly reduces the surface side reaction, improves the cycle performance, realizes high capacity retention rate, and also enhances the ion conductivity at the interface, and improves the rate performance by in-situ doping and coating high-entropy solid-state electrolyte on the surface of nickel-cobalt-manganese or nickel-cobalt-aluminum ternary positive electrode material. In addition, the modified lithium ion positive electrode material of the present application can also improve the thermal stability of the ternary positive electrode material, thereby reducing the risk of thermal runaway, and the hardness of the high-entropy solid-state electrolyte is relatively high, which can improve the hardness of the outer surface of the ternary positive electrode material, so that the mechanical stability of the ternary positive electrode material is improved.

[0149] It should be noted that although the technical solutions of the present application are introduced with specific examples, those skilled in the art can understand that the present application should not be limited thereto.

[0150] Having described various embodiments of the application, it is to be understood that the above description is meant to be illustrative only and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art, without departing from the scope and spirit of the described embodiments. The choice of words in this document is intended to best explain the principles of the embodiments, the practical application, or technical improvement over the existing technology, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A modified lithium-ion cathode material, characterized in that, Including the cathode material body and the surface coating layer, The surface coating layer is chemically composed of a high-entropy solid electrolyte, Li7La3(M). x M1 a M2 b M3 c …Mi j )2O 12 Where M is Zr or Ti, and x > 0; M1, M2, M3...Mi are elements other than Li, La, Zr and Ti, i is a positive integer and 5 ≤ i ≤ 10, a, b, c...j are the stoichiometric coefficients of each element, a, b, c...j ≥ 0, and x + a + b + c + ... + j = 1, and The modified lithium-ion cathode material further includes a shallow doped layer, which is disposed between the cathode material body and the surface coating layer. The metal elements in the shallow doped layer include all the metal elements in the cathode material body and at least one metal element in the surface coating layer.

2. The modified lithium-ion cathode material according to claim 1, wherein, The average thickness of the shallow doped layer is 5-100 nm.

3. The modified lithium-ion cathode material according to claim 1, wherein, The average thickness of the surface coating layer is 2nm-5μm.

4. The modified lithium-ion cathode material according to any one of claims 1 to 3, wherein M1, M2, M3...Mi is at least one selected from Mg, B, Ca, Sc, Ti, V, Cr, Te, Fe, Cu, Zn, Ga, Ge, Sr, Y, Nb, Mo, Ru, Sn, Sb, and W.

5. The modified lithium-ion cathode material according to any one of claims 1 to 3, wherein b = c = ... = j.

6. The modified lithium-ion cathode material according to any one of claims 1 to 3, wherein in the high-entropy solid electrolyte, the molar ratio of La to M, M1, M2, ... Mi is La:(M:M1:M2:...:Mi)=3:2(0.5-0.8:0.1:0.1:...:0.1).

7. The modified lithium-ion cathode material according to any one of claims 1 to 3, wherein, The high-entropy solid electrolyte is Li7La3(Zr) 0.5 Al 0.1 Ca 0.1 Cr 0.1 Mg 0.1 Zn 0.1 )2O 12 .

8. The modified lithium-ion cathode material according to any one of claims 1 to 3, wherein, The cathode material body includes a ternary cathode material, which includes at least one of nickel-cobalt-manganese ternary cathode material and nickel-cobalt-aluminum ternary cathode material.

9. The modified lithium-ion cathode material according to any one of claims 1 to 3, wherein, The mass ratio of the surface coating layer to the cathode material body is 0.1%-10%.

10. The modified lithium-ion cathode material according to any one of claims 1 to 3, wherein the average particle size of the modified lithium-ion cathode material is 5-15 μm.

11. A method for manufacturing a modified lithium-ion cathode material according to any one of claims 1 to 10, characterized in that, Includes the following steps: S1: Prepare the raw material salt solution A for the positive electrode material bulk, the raw material salt solution B for the high-entropy solid electrolyte, the precipitant solution C, and the complexing agent solution D respectively; S2: The raw material salt solution A, the precipitant solution C and the complexing agent solution D are subjected to a co-precipitation reaction to obtain precursor I; S3: The raw material salt solution B, the precipitant solution C, and the complexing agent solution D are further introduced into precursor I to carry out a co-precipitation reaction, yielding precursor II; and S4: The precursor II is calcined to obtain the modified lithium-ion cathode material.

12. The method for manufacturing the modified lithium-ion cathode material according to claim 11, wherein step S3 is performed in two steps: sub-step S3-1, further introducing the raw material salt solution A, the raw material salt solution B, the precipitant solution C and the complexing agent solution D into the precursor I to perform a co-precipitation reaction to obtain an intermediate precursor; and sub-step S3-2, further introducing the raw material salt solution B, the precipitant solution C and the complexing agent solution D into the intermediate precursor to perform a co-precipitation reaction to obtain precursor II.

13. The method for manufacturing the modified lithium-ion cathode material according to claim 11 or 12, wherein the raw material salt solution A is prepared using at least one of the sulfate, nitrate and chloride salts of nickel, cobalt, manganese or aluminum.

14. The method for manufacturing the modified lithium-ion cathode material according to claim 13, wherein, The total concentration of nickel, cobalt, manganese or aluminum metal ions is 1-5 mol / L.

15. The method for manufacturing the modified lithium-ion cathode material according to claim 11 or 12, wherein, The raw material salt solution B is prepared using at least one of the sulfate, nitrate and chloride salts of M1, M2, M3...Mi.

16. The method for manufacturing the modified lithium-ion cathode material according to claim 15, wherein, The total concentration of ions M1, M2, M3...Mi is 1-5 mol / L.

17. The method for manufacturing the modified lithium-ion cathode material according to claim 11 or 12, wherein, The precipitant solution C is prepared using at least one of sodium hydroxide and sodium carbonate.

18. The method for manufacturing the modified lithium-ion cathode material according to claim 11 or 12, wherein the complexing agent solution D is an aqueous ammonia solution with a concentration of 0.5-3 mol / L.

19. The method for manufacturing the modified lithium-ion cathode material according to claim 11 or 12, wherein in steps S2 and S3, the reaction temperature is 45-65°C, the reaction atmosphere is an inert gas atmosphere, and the pH value of the reaction system is 10.5-13.5, and The coprecipitation reaction was carried out under stirring at a speed of 50-500 rpm.

20. The method for manufacturing the modified lithium-ion cathode material according to claim 11 or 12, wherein, In step S4, aging and drying are carried out before calcination, and cooling is carried out after calcination.

21. The method for manufacturing the modified lithium-ion cathode material according to claim 20, wherein, After aging, the precursor II is repeatedly filtered or washed with deionized water until the pH of the supernatant is neutral.

22. The method for manufacturing the modified lithium-ion cathode material according to claim 20, wherein in step S4, the aging temperature is 30-70°C and the aging time is 5-15 hours; and The drying temperature is 65-115℃, and the drying time is 6-12 hours.

23. The method for manufacturing the modified lithium-ion cathode material according to claim 11 or 12, wherein in step S4, the precursor II and a relatively excess lithium source are weighed according to the stoichiometric ratio, ball-milled and mixed evenly, and then subjected to two-stage high-temperature calcination.

24. The method for manufacturing the modified lithium-ion cathode material according to claim 23, wherein, The stoichiometric ratio of the lithium source to the precursor II, expressed as molar amounts of metal ions, is 1.1-1.5; and The lithium source is at least one selected from Li2CO3, LiOH, and LiAc.

25. The method for manufacturing the modified lithium-ion cathode material according to claim 23, wherein in the two-stage high-temperature calcination, the sintering temperature of the first stage is 350-650℃ and the holding time is 1-8h; the sintering temperature of the second stage is 650-950℃ and the holding time is 6-20h.

26. A lithium-ion battery, comprising a positive electrode and a negative electrode, characterized in that, The positive electrode includes a modified lithium-ion positive electrode material according to any one of claims 1 to 10, or a modified lithium-ion positive electrode material obtained by the manufacturing method according to any one of claims 11 to 25.

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