Modified lithium ion positive electrode material and manufacturing method thereof, and lithium ion battery

Abstract

The invention relates to a modified lithium ion positive electrode material, a manufacturing method thereof and a lithium ion battery. The invention provides a modified lithium ion positive electrode material which comprises a positive electrode material body and a surface coating layer, the chemical composition of the surface coating layer is high-entropy solid electrolyte Li < 7 > La < 3 > (M < x > M < 1 > a M < 2 > b M < 3 > c... Mij) 2O12, M is Zr or Ti, and x is greater than 0; m1, M2, M3... Mi are elements other than Li, La, Zr and Ti, i is a positive integer, 5 < = i < = 10, a, b, c... j are stoichiometric coefficients of the elements, a, b, c... j > = 0, and x + a + b + c +... + j = 1. The high entropy of the solid electrolyte is realized, so that the ionic conductivity at the interface is further improved, and the problem of energy density reduction caused by surface coating is further solved through lithium enrichment.

Description

Technical Field

[0001] The present invention relates to a coated modified positive electrode material, belonging to the technical field of lithium ion batteries. Specifically, the present invention relates to a modified lithium ion positive electrode material, a method for manufacturing the same, and a lithium ion battery using the modified lithium ion positive electrode material. Background Art

[0002] As a new type of energy storage device, lithium-ion batteries have the advantages of high voltage, low self-discharge rate, and high energy density. Therefore, they are widely used in electronic products, transportation, energy storage and other fields. However, as the energy density of lithium-ion batteries increases, improving their safety performance has become a primary concern for researchers. Currently, large-scale commercial lithium-ion batteries mainly use liquid electrolytes, which are flammable and easy to leak, posing a great safety hazard.

[0003] In order to solve the above problems, researchers proposed a surface coating method to modify the ternary cathode materials, the main functions of which include inhibiting side reactions on the cathode material surface, improving electron and ion conduction, and promoting interfacial ion charge transfer. However, conventional oxides and fluorides as coating materials have no electrochemical activity and poor ion conductivity, which will increase impedance and reduce the rate performance of the material.

[0004] In recent years, high entropy oxides have attracted more and more attention as coating materials for the modification of positive electrode materials for lithium-ion batteries. High entropy oxides are a type of multi-component material with a single solid solution structure composed of five or more metal cations in equal or nearly equal amounts. 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 conducive to alleviating the disadvantage of uncontrolled lattice oxygen redox activity and helps to further improve the cycle stability of the material. As has been reported, the use of some high entropy oxides to modify the surface of positive electrode materials can avoid or reduce the direct contact between the positive electrode material and the electrolyte, alleviate the capacity decay caused by interfacial side reactions, and protect the stability of the material. Summary of the invention

[0005] Problem that the invention aims to solve

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

[0007] In order to solve the problems of the prior art, the purpose of the present invention is to provide a positive electrode material modified by a multifunctional high-entropy solid electrolyte coating layer, and a preparation method and application thereof, which, while maintaining the effects of alleviating surface side reactions and enhancing ion transport in the existing high-entropy oxide coating technology, further improves the ionic conductivity at the interface through high entropy of the solid electrolyte, and further reduces the problem of reduced energy density caused by surface coating through lithium enrichment.

[0008] Solutions for solving problems

[0009] In order to achieve the above invention purpose, the present invention adopts the following technical solution:

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

[0011] Wherein, the chemical composition of the surface coating layer is a high entropy solid electrolyte Li 7 La 3 (M x M1 a M2 b M3 c …Mi j ) 2 O 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 the stoichiometric coefficients of each element, a, b, c…j≥0, and x+a+b+c+…+j=1.

[0012] Further, according to the above-mentioned modified lithium-ion positive electrode material, the modified lithium-ion positive electrode material further includes a superficial doping layer, the superficial doping layer is arranged between the positive electrode material body and the surface coating layer, and the metal elements in the superficial 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 doped 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 above-mentioned modified lithium ion positive electrode material, 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, W,

[0016] Preferably, b=c=...=j, and

[0017] Wherein the molar ratio of La to M, M1, M2, ...Mi in the high entropy solid electrolyte 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 electrolyte is Li 7 La 3 (Zr 0.5 Al 0.1 Ca 0.1 Cr 0.1 Mg 0.1 Zn 0.1 ) 2 O 12 .

[0020] Furthermore, according to the above-mentioned modified lithium-ion positive electrode material, the positive electrode material body includes a ternary positive electrode material, and the ternary positive electrode material includes 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 electrolyte is a lithium-rich high entropy solid electrolyte;

[0022] Preferably, the mass ratio of the surface coating layer 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 invention provides a method for manufacturing the modified lithium ion positive electrode material according to the above, comprising the following steps:

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

[0026] S2: subjecting the raw material salt solution A, the precipitant solution C and the complexing agent solution D to a coprecipitation reaction 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 coprecipitation 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 materials, the step S3 is carried out 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 for 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 for co-precipitation reaction to obtain a precursor II.

[0030] Further, according to the above-mentioned method for manufacturing a modified lithium-ion positive electrode material, the raw salt solution A is prepared using at least one of a sulfate, a nitrate and a chloride of nickel, cobalt, manganese or aluminum, and 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, and preferably the total concentration of ions of M1, M2, M3 ... Mi is 1-5 mol / L;

[0032] Preferably, the precipitant solution C is prepared using at least one of sodium hydroxide and sodium carbonate, preferably at a concentration of 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] Furthermore, according to the above-mentioned method for manufacturing a modified lithium-ion positive electrode material, in the step S2 and the step 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

[0035] The coprecipitation reaction was carried out under stirring at a stirring speed of 50-500 rpm;

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

[0037] Preferably, after the aging, the precursor II is repeatedly filtered or stirred and washed with deionized water until the pH value of the supernatant is neutral;

[0038] Preferably, in step S4, the aging temperature is 30-70° C., and the aging time is 5-15 hours; and

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

[0040] Furthermore, according to the above-mentioned method for manufacturing a modified lithium-ion positive electrode material, in the step S4, the precursor II and a relatively excessive amount of lithium source are weighed according to a stoichiometric ratio, ball-milled and mixed uniformly, and then subjected to two-stage high-temperature calcination;

[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, LiAc, and

[0043] 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 hours; the sintering temperature of the second stage is 650-950° C., and the holding time is 6-20 hours.

[0044] Another aspect of the present invention provides a lithium ion battery, comprising a positive electrode and a negative electrode, wherein the positive electrode comprises the modified lithium ion positive electrode material described above or the modified lithium ion positive electrode material obtained according to the above manufacturing method.

[0045] Effects of the Invention

[0046] The technical solution proposed by the present invention has the following beneficial effects:

[0047] 1. The surface coating layer of the present invention can provide good surface protection. As a physical barrier, it can significantly reduce surface side reactions and improve cycle performance;

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

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

[0050] 4. In the lithium-rich high-entropy solid electrolyte preferably used in the present invention, the positive electrode material modified by direct sintering of the high-entropy solid electrolyte coating with excess lithium can, on the one hand, utilize the melting effect of lithium salt to reduce the sintering temperature of the solid electrolyte, so that the sintering temperature of the solid electrolyte and the positive electrode material are adapted, so as to achieve the effect of sintering the positive electrode material and the solid electrolyte coating layer at the same time and making the solid electrolyte obtain better crystallinity, while enhancing 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 lithium supplement effect, especially in the silicon-based system, it can improve the first effect and cycle performance, and make up for the defect of energy density reduction caused by common coating;

[0051] 5. The preferred high entropy material coating and bulk shallow doping of the present invention can improve the thermal stability of positive electrode materials, especially high nickel positive electrode materials, enhance the bond energy of TM-O bonds 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 present invention can improve the hardness of the outer layer. The particle hardness of the modified lithium-ion positive electrode material is not less than 150MPa, which effectively improves the mechanical strength and stability of the single particle of the positive electrode material. At the same time, it can effectively reduce the lithium-nickel mixing in the positive electrode material and improve the cycle performance.

[0053] 7. The conventional method of coating the surface of the positive electrode material with a high entropy material and then sintering it will cause the elements to form a gradient distribution in the permeation layer. However, the presence of a high-valent transition metal with controllable composition in the homogeneous high-entropy shallow bulk doping layer preferably formed in situ in the present invention causes the oxygen defects generated by the material during the cycle to be trapped around these doping atoms, forming a "pinning effect", thereby preventing these defects from further agglomerating to generate dislocations or cracks, and significantly improving the structural stability of the material during the cycle. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0055] Various exemplary embodiments, features and aspects of the present invention will be described in detail below. The word "exemplary" used here means "used as an example, embodiment or illustrative". Any embodiment described here as "exemplary" is not necessarily interpreted as being superior or better than other embodiments.

[0056] In addition, in order to better illustrate the present invention, numerous specific details are provided in the following specific embodiments. It should be understood by those skilled in the art that the present invention can be implemented without certain specific details. In other examples, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present invention.

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

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

[0059] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0060] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints A and B.

[0061] <First aspect>

[0062] The first aspect of the present invention provides a modified lithium ion positive electrode material, comprising a positive electrode material body and a surface coating layer, wherein the chemical composition of the surface coating layer is a high entropy solid electrolyte Li 7 La 3 (M x M1 a M2 b M3 c …Mi j ) 2 O 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 the stoichiometric coefficients of each element, a, b, c…j≥0, and x+a+b+c+…+j=1.

[0063] The modified lithium-ion positive electrode material of the present invention has a surface coating layer with a specific structure. The high-entropy oxide solid electrolyte forms a coating with uniform and controllable thickness and coating composition on the surface of the positive electrode material body, thereby enhancing the integrity of the coating layer. During the battery cycle, it not only does not hinder the conduction of ions but also maintains the stability of the positive electrode material, thereby improving the cycle performance of the material.

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

[0065] In one embodiment of the present invention, the modified lithium-ion positive electrode material also includes a superficial doping layer, and the superficial doping layer is arranged between the positive electrode material body and the surface coating layer, and the metal elements in the superficial doping layer include all the metal elements in the positive electrode material body and at least one metal element in the surface coating layer. Optionally, the superficial doping layer may also include other elements other than the coating layer. In a specific embodiment of the present invention, the superficial doping layer is formed by mixing a high entropy solid electrolyte with the positive electrode material body, and the average thickness of the superficial doping layer is 5-100nm, preferably 5-50nm, and more preferably 10-30nm.

[0066] In one embodiment of the present invention, the positive electrode material body includes a ternary positive electrode material, and more specifically includes 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 invention, the elements of the shallow doping layer include: transition metal elements contained in the positive electrode material and elements contained in the high entropy solid electrolyte coating layer material, more specifically including all metal elements in the positive electrode material body and part of the metal elements in the surface coating layer and other elements outside the coating layer. The structural type of the shallow doping layer is a homogeneous, highly disordered multi-component system formed by the co-precipitation reaction of the salt solution in the nickel-cobalt-manganese or nickel-cobalt-aluminum ternary positive electrode material described later and the salt solution for generating the high entropy oxide solid electrolyte. The high entropy doped disordered system is introduced into the layered structure of the ternary material to form a "pinning effect", stabilize its multi-electron reaction, achieve the suppression of oxygen loss, dislocation generation and harmful phase change, promote the rapid diffusion of lithium ions, 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 the “homogeneous” in the structural type of the shallow doping layer means that the elements in the shallow doping layer are evenly distributed in the layer without concentration gradient.

[0069] In one embodiment of the present invention, the average thickness of the surface coating layer is 2nm-5μm, preferably 5nm-0.5μm. If the surface coating layer is too thick, the lithium ion transmission path will be extended, resulting in a decrease in charge transmission performance and a large loss in specific capacity; if it is too thin, the material performance will not be significantly improved.

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

[0071] In one embodiment of the present invention, 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 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 one embodiment of the present invention, the mass ratio of the surface coating layer to the cathode 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 the surface coating layer is too little, a uniform coating cannot be formed, and the protective effect and hardness improvement effect of the hard surface coating layer on the body material cannot be exerted.

[0073] In one embodiment of the present invention, 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 invention, the high entropy solid electrolyte is a lithium-rich high entropy solid electrolyte. In a preferred embodiment of the present invention, 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, Li 7 La 3 (Zr 0.5 Al 0.1 Ca 0.1 Cr 0.1 Mg 0.1 Zn 0.1 ) 2 O 12. In addition to La and Zr, five other metal elements are also included. The atomic sizes of the five elements Al, Ca, Cr, Mg and Zn are close, and they can form a uniform mixed phase, which is easy to achieve a stable high entropy structure, and can produce a large mixing entropy value, which is conducive to the formation of a solid solution structure. Therefore, the combination of these elements is preferably used as the high entropy solid electrolyte of the present invention.

[0075] Figure 1 Schematic diagram of in-situ high entropy solid electrolyte doping, coating and co-modification of lithium-ion battery cathode materials. Figure 1 As shown, the modified lithium ion positive electrode material of the present invention comprises a body of a nickel-cobalt-manganese ternary positive electrode material, a shallow doping layer and a surface coating layer, wherein the shallow doping layer is a mixture of a nickel-cobalt-manganese ternary positive electrode material and a high entropy solid electrolyte, and the surface coating layer is a high entropy solid electrolyte layer, and the high entropy solid electrolyte can be specifically Li 7 La 3 (Zr 0.5 Al 0.1 Ca 0.1 Cr 0.1 Mg 0.1 Zn 0.1 ) 2 O 12 .

[0076] <Second Aspect>

[0077] A second aspect of the present invention provides a method for manufacturing a modified lithium ion positive electrode material, the manufacturing method comprising the following steps:

[0078] S1: respectively preparing a raw salt solution A of the cathode material body, a raw salt solution B of the high entropy solid electrolyte, a precipitant solution C and a complexing agent solution D;

[0079] S2: subjecting the raw material salt solution A, the precipitant solution C and the complexing agent solution D to a coprecipitation reaction 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 for coprecipitation 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 invention can achieve a coating effect with uniform and controllable thickness and coating composition through co-precipitation in-situ coating, thereby fully exerting the role of the surface coating layer of the high entropy solid electrolyte and improving 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 cathode material body and the raw materials for forming the high entropy solid electrolyte. For example, water can be used.

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

[0085] By selectively pumping in a mixed salt solution of different elements in sub-step S3-1, some of the constituent elements can be mixed into the shallow doping layer. In addition, since the mixed salt solution of different elements is selectively pumped in by co-precipitation, the metal elements are uniformly distributed in the shallow permeation layer. Preferably, in sub-step S3-1, all the constituent elements constituting the high entropy solid electrolyte are pumped into the reaction vessel and fully reacted, and a structure in which the constituent elements of the positive electrode material body and all the constituent elements of the high entropy solid electrolyte coating layer material are mixed is formed in the shallow doping layer. Therefore, in the shallow doping layer, the constituent elements of the high entropy solid electrolyte material will occupy the octahedral or tetrahedral sites in the transition metal layer or lithium ion layer in the positive electrode material body structure, forming a derivative structure including one or more structures of a layered structure, a spinel structure, a rock salt structure or a disordered structure.

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

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

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

[0089] In one embodiment of the present invention, in step S2 and step 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 coprecipitation reaction is carried out under stirring at a stirring speed of 50-500 rpm, preferably 200-500 rpm. By keeping the pH of the reaction system alkaline, the coprecipitation reaction can be carried out smoothly.

[0090] In one embodiment of the present invention, in step S4, aging and drying are performed before calcination, and cooling is performed after calcination. After aging, the precursor II is repeatedly filtered or stirred and washed with deionized water until the pH value of the supernatant is neutral.

[0091] In one embodiment of the present invention, 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 one embodiment of the present invention, in step S4, the precursor II and a relatively excess lithium source are weighed according to the stoichiometric ratio, and after ball milling and mixing, two-stage high-temperature calcination is performed. In a preferred embodiment of the present invention, 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 positive electrode material coated and modified by the high-entropy solid electrolyte in a state of excess lithium, on the one hand, the melting effect of the lithium salt can be utilized to reduce the sintering temperature of the solid electrolyte, and on the other hand, the excess lithium source can achieve a lithium supplement effect, especially in a silicon-based system, it can improve the first effect and cycle performance, and make up for the defect of the common coating causing a decrease in energy density.

[0093] In one embodiment of the present invention, the lithium source is selected from Li 2 CO 3 , LiOH, LiAc. In one embodiment of the present invention, in the two-stage high-temperature calcination, the sintering temperature of the first stage is 350-650°C, and the holding time is 1-8h; the sintering temperature of the second stage is 650-950°C, and the holding time is 6-20h. In addition, there is no particular restriction on the sintering atmosphere. Sintering can be carried out in a gas atmosphere of air, oxygen, or air with adjusted oxygen partial pressure.

[0094] Through the first low-temperature sintering, the components in the material are evenly distributed, the pores and defects in the material are eliminated, the lithium carbonate is decomposed into oxides, the waste gas is discharged, the density of the material is improved and the integrity of the crystal structure, the grain size of the material is gradually reduced, and the crystallinity is initially 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 better electrochemical properties.

[0095] In a specific embodiment of the present invention, a method for preparing a ternary positive electrode material modified by a multifunctional high entropy solid electrolyte coating layer is provided, wherein the preparation steps are as follows: a salt solution, a complexing agent solution, and a precipitant solution are respectively introduced into a reaction kettle, stirred for reaction at a certain temperature for a period of time, and then allowed to stand for aging, and after aging, washing and drying are performed, and the dried precursor is evenly mixed with a lithium source and then sintered at a high temperature to obtain a ternary material coated with a high entropy oxide solid electrolyte. The preparation process comprises the following steps:

[0096] (1) preparing a mixed salt solution A of nickel, cobalt and manganese according to a stoichiometric ratio, preferably, the nickel salt, cobalt salt, manganese salt or aluminum salt is 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] Dissolving soluble La salt, Zr salt, M1 salt, M2 salt, ...Mi salt in deionized water according to a stoichiometric ratio to obtain a mixed salt solution B, preferably, La, Zr, M1, M2, ...Mi can form a high entropy oxide solid 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] Prepare a precipitant solution C, preferably, the precipitant includes at least one of sodium hydroxide and sodium carbonate, with a concentration of 3-5 mol / L;

[0099] Prepare a complexing agent solution D, preferably, the complexing agent is ammonia water with a concentration of 0.5-3 mol / L;

[0100] (2) introducing a mixed salt solution A, a precipitant solution C and a complexing agent solution D into a reaction vessel to carry out a coprecipitation reaction to obtain a precursor I;

[0101] (3) introducing mixed salt solutions A and B, precipitant solution C and complexing agent solution D into the reactor in parallel to perform a coprecipitation reaction to obtain precursor II;

[0102] (4) introducing a mixed salt solution B, a precipitant solution C and a complexing agent solution D into a reaction vessel to carry out a coprecipitation reaction to obtain a precursor III;

[0103] (5) aging the mixed solution after the reaction in step (3), preferably, the aging temperature is 30 to 70° C., and the aging time is 5 to 15 hours;

[0104] (6) washing the mixed solution after aging in step (4) with deionized water until the pH value of the supernatant is neutral. Preferably, the mixture is repeatedly filtered or stirred and washed with deionized water;

[0105] (7) drying the washed material in step (5), preferably at a drying temperature of 65° C. to 115° C. for a drying time of 6 h to 12 h, to obtain a coated ternary material precursor;

[0106] (8) Weigh the coating precursor and a relatively excess lithium source according to the stoichiometric ratio. Preferably, the lithium source is Li 2 CO 3 , LiOH, and LiAc, are evenly mixed by ball milling, and then preferably subjected to two-stage high-temperature calcination in an air or oxygen atmosphere, and naturally cooled to obtain a ternary material coated with a high-entropy solid electrolyte layer and shallowly doped.

[0107] Preferably, the mixed salt solution B in step (1) has a plurality of different element mixing formulas, which are prepared simultaneously and placed in at least two tanks, namely B, B1, B2...Bi.

[0108] Preferably, the temperature of the coprecipitation reaction in step (2), step (3) and step (4) is 45-65° C., the reaction atmosphere is a 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 step (2), step (3) and step (4) is 30-60° C.; during the introduction of the salt solution, the stirring paddle in the reactor is kept stirring at a stirring rate of 50-500 rpm.

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

[0111] <Third Aspect>

[0112] A third aspect of the present invention provides a lithium ion battery, wherein the lithium ion battery comprises the modified lithium ion positive electrode material as described above or the modified lithium ion positive electrode material obtained by the manufacturing method as described above.

[0113] Since the modified lithium ion positive electrode material of the present invention significantly reduces the interfacial side reactions due to the uniformity, hardness and strength of the surface coating layer, while improving the mechanical strength and stability of the ternary positive electrode material particles, it can enhance the ionic conductivity at the interface and improve the rate performance. Therefore, the lithium ion battery using the modified lithium ion positive electrode material of the present invention can ensure excellent battery performance and good safety performance.

[0114] The lithium-ion battery of the present invention includes necessary components such as a positive electrode plate, a negative electrode plate, an electrolyte, and other necessary or auxiliary components.

[0115] Example

[0116] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0117] Example 1

[0118] This embodiment provides a method for preparing an in-situ high-entropy solid electrolyte doping, coating and co-modification 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; prepare a mixed solution B of metal nitrates, 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 the metal elements of lanthanum, zirconium, aluminum, calcium, chromium, magnesium and zinc is 3 mol / L; prepare a sodium hydroxide solution C with a concentration of 3 mol / L as a precipitant. Prepare an ammonia solution with a concentration of 3 mol / L as a complexing agent.

[0120] (2) Solution A, Solution C, and Solution D were simultaneously pumped into the reactor. The stirring rate of the stirring paddle in the reactor was 500 rpm and the reaction temperature was 55°C. When the particle size of the precipitate reached 10 μm, the addition was stopped and the amount of mixed salt introduced was recorded.

[0121] (3) Solution A, solution B, solution C, and solution D are pumped into the reactor simultaneously. The stirring rate of the stirring paddle in the reactor is 500 rpm and the reaction temperature is 55° C. When the mass of the solute in the metal salt of the mixed solution B is 0.5% of the mass of the solute in solution A in step 2 and step 3 added simultaneously with solution B, the addition is stopped.

[0122] (4) Solution B, solution C, and solution D are pumped into the reactor simultaneously. The stirring rate of the stirring paddle in the reactor is 500 rpm and the reaction temperature is 55° C. When the mass of the solute in the metal salt of the mixed solution B is 1% of the mass of the salt solute in step 3, the addition is stopped.

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

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

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

[0126] (8) The precursor obtained in (7) and 1.2 times excess lithium carbonate were weighed according to the stoichiometric ratio, and the mixture was placed in a mullite sagger after being evenly mixed by ball milling, and calcined at 550° C. for 6 hours, and then calcined at 900° C. for 10 hours, and naturally cooled to obtain Li 7 La 3 (Zr 0.5 Al 0.1 Ca 0.1 Cr 0.1 Mg 0.1 Zn 0.1 ) 2 O 12 A coated and shallowly doped modified lithium-rich ternary positive electrode material, wherein the average particle size of the modified lithium-ion positive electrode material is 11 μm, the average thickness of the surface coating layer is 50 nm, the mass ratio of the surface coating layer to the positive electrode material body is 2%, and the average thickness of the shallow doping layer is 30 nm.

[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 for changing the reaction time in step (3) so that the average thickness of the shallow doping layer is 5 nm, the rest is the same as Example 1.

[0131] Example 4

[0132] Except for changing the reaction time in step (3) so that the average thickness of the shallow doped layer is 50 nm, the rest is the same as Example 1.

[0133] Example 5

[0134] Except for changing the reaction time in step (4) so ​​that the average thickness of the surface coating layer is 5 nm, the rest is the same as Example 1.

[0135] Example 6

[0136] Except for changing the reaction time in step (4) so ​​that the average thickness of the surface coating layer is 0.5 μm, the rest is the same as Example 1.

[0137] Example 7

[0138] Except that step (3) is not performed and a shallow doping layer is not provided, the rest is the same as that of Example 1.

[0139] Example 8

[0140] Except that the 1.2 times excess lithium carbonate in step (8) is replaced with 1.0 times to make the high entropy solid electrolyte non-lithium-rich, the rest is the same as Example 1.

[0141] Comparative Example 1

[0142] Except for not performing the operations of step (3) and step (4), 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 or doped with a high entropy solid electrolyte, and its cycle performance and material thermal stability are relatively poor.

[0143] Comparative Example 2

[0144] Except for removing zirconium nitrate and lanthanum nitrate from the mixed solution B and not performing step (3), the rest is the same as in Example 1 to obtain a high entropy oxide Li (Al 0.2 Ca 0.2 Cr 0.2 Mg 0.2 Zn 0.2 ) 2 Coated and modified lithium-ion battery cathode materials.

[0145] The modified lithium-ion positive electrode materials obtained in the above embodiments and comparative examples were applied to button batteries and subjected to charge and discharge tests at room temperature (25°C) using a button battery testing system. The tests were conducted at a discharge rate of 0.1C and a voltage range of 2.75-4.25. The initial efficiency of button charging and the capacity retention rate after 100 cycles were recorded, and the decomposition temperature of the material was tested by DSC.

[0146] Table 1

[0147] First effect (%) Capacity retention rate (%) Thermal decomposition temperature (℃) 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 cathode material of the present invention significantly reduces the surface side reaction, improves the cycle performance, achieves a high capacity retention rate, and also enhances the ionic conductivity at the interface, thereby improving the rate performance. In addition, the modified lithium-ion cathode material of the present invention can also improve the thermal stability of the ternary cathode material, thereby reducing the risk of thermal runaway, and the high entropy solid electrolyte has a high hardness, which can improve the outer surface hardness of the ternary cathode material, thereby improving the mechanical stability of the ternary cathode material.

[0149] It should be noted that, although the technical solution of the present invention is introduced with specific examples, those skilled in the art will appreciate that the present invention should not be limited thereto.

[0150] The embodiments of the present invention have been described above, and the above description is exemplary, 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 terms used herein are selected to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A modified lithium ion positive electrode material, characterized in that: Including positive electrode material body and surface coating layer, Wherein, the chemical composition of the surface coating layer is a high entropy solid 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 the stoichiometric coefficients of each element, a, b, c…j≥0, and x+a+b+c+…+j=1.

2. The modified lithium ion positive electrode material according to claim 1, wherein the modified lithium ion positive electrode material further comprises a superficial doping layer, wherein the superficial doping layer is disposed between the positive electrode material body and the surface coating layer, and the metal elements in the superficial doping layer include all the metal elements in the positive electrode material body and at least one metal element in the surface coating layer; Preferably, the average thickness of the shallow doped layer is 5-100 nm, preferably 5-50 nm; Preferably, the average thickness of the surface coating layer is 2 nm-5 μm, preferably 5 nm-0.5 μm.

3. The modified lithium ion positive electrode material according to claim 1 or 2, wherein 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 Wherein the molar ratio of La to M, M1, M2, ...Mi in the high entropy solid electrolyte is La:(M:M1:M2:...:Mi)=3:2(0.5-0.8:0.1:0.1:...:0.1); Preferably, i=5, M is Zr, and M1, M2, M3, M4 and M5 are Al, Ca, Cr, Mg and Zn respectively; Preferably, 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 .

4. The modified lithium-ion cathode material according to any one of claims 1 to 3, wherein the cathode material body comprises a ternary cathode material, and the ternary cathode material comprises at least one of a nickel-cobalt-manganese ternary cathode material and a nickel-cobalt-aluminum ternary cathode material; Preferably, the high entropy solid electrolyte is a lithium-rich high entropy solid electrolyte; Preferably, the mass ratio of the surface coating layer to the positive electrode material body is 0.1%-10%, preferably 1%-5%; Preferably, the average particle size of the modified lithium ion positive electrode material is 5-15 μm, preferably 5-10 μm.

5. A method for producing a modified lithium ion positive electrode material according to any one of claims 1 to 4, characterized in that: The steps include: S1: respectively preparing a raw salt solution A of the cathode material body, a raw salt solution B of the high entropy solid electrolyte, a precipitant solution C and a complexing agent solution D; S2: subjecting the raw material salt solution A, the precipitant solution C and the complexing agent solution D to a coprecipitation reaction to obtain a precursor I; S3: further introducing the raw salt solution B, the precipitant solution C and the complexing agent solution D into the precursor I for coprecipitation reaction to obtain a precursor II; and S4: calcining the precursor II to obtain the modified lithium ion positive electrode material.

6. The method for manufacturing a modified lithium ion positive electrode material according to claim 5, wherein the 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 for a coprecipitation 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 for a coprecipitation reaction to obtain a precursor II.

7. The method for producing a modified lithium ion positive electrode material according to claim 5 or 6, wherein the raw salt solution A is prepared using at least one of sulfate, nitrate and chloride 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 B is prepared using at least one of sulfate, nitrate and chloride of M1, M2, M3 ... Mi, and preferably the total concentration of ions of M1, M2, M3 ... Mi is 1-5 mol / L; Preferably, the precipitant solution C is prepared using at least one of sodium hydroxide and sodium carbonate, preferably at a concentration of 3-5 mol / L; and The complexing agent solution D is an ammonia solution with a concentration of 0.5-3 mol / L.

8. The method for producing a modified lithium ion positive electrode material according to any one of claims 5 to 7, wherein in step S2 and step 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 coprecipitation reaction was carried out under stirring at a stirring speed of 50-500 rpm; Preferably, in step S4, aging and drying are performed before calcination, and cooling is performed after calcination; Preferably, after the aging, the precursor II is repeatedly filtered or stirred and washed with deionized water until the pH value of the supernatant is neutral; Preferably, 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 6-12h.

9. The method for manufacturing a modified lithium-ion positive electrode material according to any one of claims 5 to 8, wherein in step S4, the precursor II and a relatively excessive amount of lithium source are weighed according to a stoichiometric ratio, ball-milled and mixed to be uniform, and then subjected to two-stage high-temperature calcination; Preferably, the stoichiometric ratio of the lithium source to the precursor II in terms of metal ion moles is 1.1-1.5; Preferably, the lithium source is at least one selected from Li2CO3, LiOH, LiAc, and 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 hours; the sintering temperature of the second stage is 650-950° C., and the holding time is 6-20 hours.

10. A lithium ion battery comprising a positive electrode and a negative electrode, characterized in that: The positive electrode includes the modified lithium ion positive electrode material according to any one of claims 1 to 4, or the modified lithium ion positive electrode material obtained by the production method according to any one of claims 5 to 9.

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