WO2023039877A1

WO2023039877A1 - Positive electrode material, electrochemical device, and electronic device

Info

Publication number: WO2023039877A1
Application number: PCT/CN2021/119305
Authority: WO
Inventors: 刘小浪
Original assignee: 宁德新能源科技有限公司
Priority date: 2021-09-18
Filing date: 2021-09-18
Publication date: 2023-03-23
Also published as: CN114788051B; CN114788051A; CN118016978A

Abstract

The present application relates to a positive electrode material, an electrochemical device, and an electronic device. The positive electrode material comprises composite particles, the composite particles comprising lithium fluoride and a transition metal fluoride, wherein the molar ratio x of the lithium fluoride to the transition metal fluoride satisfies 0<x≤0.135. The positive electrode material is simple in preparation process, low in device requirement, high in yield and easy to realize scale production; and when the positive electrode material is used for an electrochemical device, the charging and discharging performance and the cycling stability of the electrochemical device can be effectively improved.

Description

A kind of cathode material, electrochemical device and electronic device

technical field

The present application relates to the field of energy storage, in particular to a positive electrode material, an electrochemical device and an electronic device.

Background technique

Compared with traditional rechargeable batteries, lithium-ion batteries are an ideal energy storage device due to their high energy density and long service life. Since commercialization, lithium-ion batteries have been widely used in portable electronic products such as smartphones, laptops, and charging treasures, and have gradually occupied the markets of new energy vehicles and large-scale grid energy storage. However, limited by its own electrochemical reaction mechanism and crystal structure, the current commercialized lithium-ion battery cathode materials have encountered a bottleneck in the specific capacity improvement, and it is difficult to meet the higher requirements of future fields such as 5G, new energy vehicles and smart grid energy storage. Energy Density Battery Requirements. In order to develop lithium-ion batteries with higher energy density, the development of a new generation of cathode materials different from traditional intercalation materials has become a research hotspot in the field of new energy.

As an alternative to traditional intercalation-type chemistries, metal fluorides are promising cathode materials for lithium secondary batteries. Metal fluorides have a typical multi-electron conversion reaction mechanism, and 1 mol of the compound can react with more than 2 mol of lithium ions, so the capacity of this type of material is many times that of the intercalation compound, and has a higher specific capacity. In addition, due to the strong electronegativity and large free energy of fluorine element, after forming a compound with metal elements, a strong ionic bond can be formed between the metal and fluorine, so this type of material generally has a high working voltage. Taking FeF ₃ as an example, when the three-electron conversion reaction occurs, the theoretical specific capacity is as high as 712mAh/g, the voltage plateau is about 2.7V, and the theoretical energy density is much higher than that of LiFePO ₄ (LFP), LiNi _x Mn _y Co _z O ₂ (NMC ), LiNi _x Co _y Al _z O ₂ (NCA), LiCoO ₂ (LCO) and other traditional cathode materials.

However, metal fluorides currently face problems such as low gram capacity and fast cycle decay as cathode materials. First of all, metal fluorides have strong ionicity and usually have a large energy band width, which makes them exhibit extremely low conductivity, and the ion mobility is low and the conversion reaction kinetics is slow, and the battery polarization is large during charge and discharge. . Secondly, during the repeated conversion reaction cycles, the nano-metal elemental particles continue to agglomerate and continuously coarsen, and are very prone to side reactions with the electrolyte, which will not only cause the loss of active materials, but may also damage the originally stable solid-state electrolyte membrane. In response to the above problems, researchers have carried out a lot of modification research work. For example, Kim et al. (Kim T, Jae W J, Kim H, et al. A cathode material for lithium-ion batteries based on graphitized carbon-wrapped FeF ₃ nanoparticles prepared by facile polymerization[J]. Journal of Materials Chemistry A, 2016 , 4(38):14857-14864.) using FeCl ₃ as iron source, citric acid (C ₆ H ₈ O ₇ ) as carbon source and chelating agent, ethylene glycol as cross-linking agent, followed by heat treatment using HF gas, _FeF3 is wrapped in graphite particles to obtain carbon-coated _FeF3 composite material. Compared with pure FeF ₃ , the prepared carbon-coated FeF ₃ composite has higher capacity and more stable cycle performance. Fan et al. (Fan X, Hu E, Ji X, et al. High energy-density and reversibility of iron fluoride cathode enabled via an intercalation extrusion reaction [J]. Nature Communications, 2018, 9:2324) reported that FeF ₃ 3H Co-O co-doped FeOF nanomaterials were prepared by hydrothermal reaction with ₂ O and CoF ₃ as solute and n-propanol as solvent. Compared with _FeF3 , the Fe-O covalent bond in FeOF replaces part of the Fe-F ionic bond, which improves the intrinsic conductivity of the material. stable cycle performance. Fu et al. (Fu W, Zhao E, Sun Z, et al.Iron Fluoride-Carbon Nanocomposite Nanofibers as Free-Standing Cathodes for High-Energy Lithium Batteries[J].Advanced Functional Materials, 2018, 28(32):1801711) The FeF ₃ /C composite fiber material was prepared by encapsulating FeF ₃ in carbon nanofibers by electrospinning process. The composite fiber material can not only maintain the FeF ₃ particles at the nanometer level, but also protect the structure of the FeF ₃ from being destroyed. At the same time, carbon nanofibers provide good channels for the rapid transfer of ions and electrons, and can also reduce unnecessary reactions between the electrolyte and the _FeF3 surface. According to the charge and discharge test, after 400 cycles, the FeF ₃ /C composite fiber material still has a reversible capacity of 500mAh/g.

The above studies have improved the electrochemical performance of metal fluorides to a certain extent, but the disadvantages are the need to use highly dangerous HF gas, or the material yield is low, the cost is high, and mass production is extremely difficult.

Contents of the invention

In order to solve the problems existing in the prior art, the application provides a positive electrode material, which has a simple preparation process, low equipment requirements, high yield, and is easy to realize large-scale production; and when used in electrochemical devices, it can effectively improve the Charge-discharge performance and cycle stability of electrochemical devices.

In the first aspect, the present application provides a positive electrode material, the positive electrode material includes composite particles, the composite particles include lithium fluoride and transition metal fluoride, wherein the molar ratio x of lithium fluoride and transition metal fluoride satisfies: 0 <x≤0.135. In this application, by compounding transition metal fluoride and a certain proportion of lithium fluoride, the fluoride ion is always kept in excess during the charging process, which can ensure that the metal ion is completely converted into a stable metal fluoride, thereby avoiding a large amount of metal ions in the positive electrode. , and then realize the high discharge specific capacity and high cycle stability of the material. In addition, by compounding lithium fluoride, no other impurity elements are introduced, which will not affect other performances of the electrochemical device. The introduced lithium can also provide some active lithium, which can further improve the electrochemical stability of the electrochemical device.

According to some embodiments of the present application, the molar ratio x of lithium fluoride and transition metal fluoride in the composite particle satisfies: 0.025≤x≤0.11. When the content of lithium fluoride in the composite particles is too low, the improvement of the performance of the electrochemical device is not obvious; when the content of lithium fluoride is too high, since lithium fluoride does not provide the discharge capacity and its intrinsic conductivity is extremely low, If the content is too high, the discharge gram capacity of the positive electrode material will be reduced.

According to some embodiments of the present application, in the X-ray spectrum of the composite particles, there are peaks between 23° and 24° in 2θ, and the half width of the peaks is 0.15° to 0.3°. The half-width of the above-mentioned peaks of the composite particles within the above-mentioned range indicates that the degree of lattice order of the composite particles is reduced, and the mixing between LiF and transition metal fluorides is more uniform. According to some embodiments of the present application, the grain size of the composite particles is 30 nm to 100 nm, wherein the grain size is calculated by Scherrer formula.

According to some embodiments of the present application, in the transition metal fluoride, the molar ratio y of the fluorine element to the transition metal element satisfies: 2≤y≤3.

According to some embodiments of the present application, the positive electrode material satisfies at least one of the following conditions (a) to (b): (a) the transition metal includes at least one of Fe, Co, Ni, Mn or Cu; ( b) The transition metal fluoride includes at least one of FeF ₃ , CoF ₃ , Fe _0.9 Co _0.1 F ₃ , NiF ₃ , MnF ₃ , FeF ₂ , CoF ₂ , NiF ₂ or CuF ₂ . According to some embodiments of the present application, in the positive electrode material, the transition metal includes at least one of Fe, Co, Ni, Mn or Cu. According to some embodiments of the present application, in the positive electrode material, the transition metal fluoride includes FeF ₃ , CoF ₃ , Fe _0.9 Co _0.1 F ₃ , NiF 3 , MnF ₃ , FeF ₂ , CoF ₂ _, NiF ₂ or CuF ₂ at least one.

In a second aspect, the present application provides a method for preparing a positive electrode material, which includes the following steps: mixing lithium fluoride and transition metal fluoride to obtain a first mixture, wherein the molar ratio of lithium fluoride and transition metal fluoride is z satisfies: 0<z≦0.13; and heat-treating the first mixture.

According to some embodiments of the present application, the preparation method satisfies at least one of the following conditions (a) to (d): (a) the transition metal includes at least one of Fe, Co, Ni, Mn or Cu; (b ) transition metal fluorides include at least one of FeF ₃ , CoF ₃ , Fe _0.9 Co _0.1 F ₃ , NiF ₃ , MnF ₃ , FeF ₂ , CoF ₂ , NiF ₂ or CuF ₂ ; (c) lithium fluoride and transition The molar ratio z of the metal fluoride satisfies: 0.03≤z≤0.1; (d) the heat treatment temperature is 200°C to 400°C, and the heat treatment time is 6h to 24h. According to some embodiments of the present application, the transition metal includes at least one of Fe, Co, Ni, Mn or Cu; the molar ratio z of lithium fluoride and transition metal fluoride satisfies: 0.03≤z≤0.1; the temperature of heat treatment is 200°C to 400°C, the heat treatment time is 6h to 24h. According to some embodiments of the present application, in the preparation method, the transition metal fluoride includes FeF ₃ , CoF ₃ , Fe _0.9 Co _0.1 F ₃ , NiF 3 , MnF ₃ , FeF ₂ , CoF ₂ _, NiF ₂ or CuF ₂ At least one; the molar ratio z of lithium fluoride and transition metal fluoride satisfies: 0.03≤z≤0.1; the temperature of heat treatment is 200°C to 400°C, and the time of heat treatment is 6h to 24h.

According to some embodiments of the present application, the molar ratio z of lithium fluoride and transition metal fluoride satisfies: 0.03≤z≤0.1. When the content of lithium fluoride is too low, the improvement of the performance of the electrochemical device by the prepared positive electrode material is not obvious; when the content of lithium fluoride is too high, since lithium fluoride does not provide the discharge capacity, and its intrinsic conductivity Low, too high content will reduce the discharge gram capacity of the prepared positive electrode material.

According to some embodiments of the present application, the temperature of the above heat treatment is 200°C to 400°C. According to some embodiments of the present application, the heat treatment time is 6h to 24h. When the heat treatment temperature is too low, the atoms cannot overcome the diffusion barrier, and the diffusion is difficult to proceed, so the prepared positive electrode material exhibits poor electrochemical performance. When the heat treatment temperature is too high, on the one hand, the transition metal fluoride may react with the adsorbed oxygen on its surface or the air introduced by the tube furnace due to poor sealing, resulting in the formation of inert impurity phases. It is easy to decompose to generate low-valent metal fluorides, which will lead to the reduction of the electrochemical performance of the obtained positive electrode material.

In a third aspect, the present application provides an electrochemical device, which includes a positive electrode, and the positive electrode includes the positive electrode material described in the first aspect of the present application or the positive electrode material prepared by the method described in the second aspect.

According to some embodiments of the present application, after the electrochemical device is fully charged, the positive electrode material includes LiF and MF _y , wherein, 2≤y≤3, and M includes at least one transition metal. According to some embodiments of the present application, M includes at least one of Fe, Co, Ni, Mn or Cu.

In a fourth aspect, the present application provides an electronic device, which includes the electrochemical device described in the third aspect of the present application.

The present application provides a positive electrode material, which includes composite particles of lithium fluoride and transition metal fluoride. Compared with conventional metal fluorides, the positive electrode material can suppress the dissolution of metal ions in the electrochemical device during charge and discharge, and achieve higher discharge specific capacity and cycle stability. In addition, the positive electrode material provided by the present application has a simple preparation process, low equipment requirements, and is easy to realize large-scale production.

Description of drawings

FIG. 1 is the XRD pattern of the positive electrode material in Comparative Example 1 and Example 1 to Example 5 of the present application.

FIG. 2 is an SEM image of the positive electrode material in Example 2 of the present application.

FIG. 3 shows the comparison of the second cycle discharge curves of the positive electrode materials in Examples 6 to 10 of the present application and Comparative Example 3. FIG.

Fig. 4 shows the cyclic voltammetry curve of the electrochemical device in Example 10 of the present application.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of them. example. The related examples described herein are illustrative in nature and are used to provide a basic understanding of the application. The examples of the present application should not be construed as limiting the present application.

For the sake of brevity, only certain numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with any other lower limit to form an unexpressed range, just as any upper limit can be combined with any other upper limit to form an unexpressed range. Furthermore, each individually disclosed point or individual value may serve as a lower or upper limit by itself in combination with any other point or individual value or with other lower or upper limits to form an unexpressly recited range.

In the description herein, unless otherwise specified, "above" and "below" include the number.

Unless otherwise stated, the terms used in the present application have the known meanings generally understood by those skilled in the art. Unless otherwise stated, the values of the parameters mentioned in the present application can be measured by various measurement methods commonly used in the art (for example, can be tested according to the methods given in the examples of the present application).

A list of items to which the terms "at least one of", "at least one of", "at least one of" or other similar terms are concatenated can mean any combination of the listed items. For example, if the items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if the items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may comprise a single component or multiple components. Item B may comprise a single component or multiple components. Item C may comprise a single component or multiple components.

1. Cathode material

In the first aspect, the present application provides a positive electrode material, the positive electrode material includes composite particles, the composite particles include lithium fluoride and transition metal fluoride, wherein the molar ratio x of lithium fluoride and transition metal fluoride satisfies: 0 <x≤0.135.

Conventional single metal fluoride cathode materials first generate nano-metal element particles and LiF during the discharge process; during the subsequent charging process, the nano-metal element is oxidized into metal ions, and recombines with fluorine ions to form metal fluoride. Since nanomaterials are prone to segregation or agglomeration, there may not be enough fluorine ions around the metal ions generated by oxidation during the charging process to combine with them to form stable metal fluorides. Excess metal ions are easily dissolved into the electrolyte, and have side reactions with the electrolyte, or shuttle to the negative electrode, and are reduced to metal dendrites. These irreversible reaction processes will not only cause the loss of the positive active material and rapidly decay the gram capacity of the electrochemical device, but also cause a short circuit inside the electrochemical device due to the metal dendrite piercing the separator, resulting in cyclic diving, and even safety hazards. ACCIDENT.

In this application, by compounding transition metal fluoride and a certain proportion of lithium fluoride, the fluoride ion is always kept in excess during the charging process, which can ensure that the metal ion is completely converted into a stable metal fluoride, thereby avoiding a large amount of metal ions in the positive electrode. , and then realize the high discharge specific capacity and high cycle stability of the material. In addition, by compounding lithium fluoride, no other impurity elements are introduced, which will not affect other performances of the electrochemical device. The introduced lithium can also provide some active lithium, which can further improve the electrochemical stability of the electrochemical device.

According to some embodiments of the present application, the molar ratio x of lithium fluoride and transition metal fluoride in the composite particle is 0.01, 0.02, 0.035, 0.04, 0.045, 0.055, 0.065, 0.07, 0.075, 0.085, 0.09, 0.095, 0.11 , 0.12, or a range of any two of these values. When the content of lithium fluoride in the composite particles is too low, the improvement of the performance of the electrochemical device is not obvious; when the content of lithium fluoride is too high, since lithium fluoride does not provide the discharge capacity and its intrinsic conductivity is extremely low, If the content is too high, the discharge gram capacity of the positive electrode material will be reduced.

In some embodiments, the molar ratio x of lithium fluoride to transition metal fluoride in the composite particle satisfies: 0.025≤x≤0.11. In some embodiments, the molar ratio x of lithium fluoride to transition metal fluoride in the composite particle satisfies: 0.03≤x≤0.1. In some embodiments, the molar ratio x of lithium fluoride to transition metal fluoride in the composite particle satisfies: 0.05≤x≤0.08.

According to some embodiments of the present application, in the X-ray spectrum of the composite particles, there are peaks between 23° and 24° in 2θ, and the half width of the peaks is 0.15° to 0.3°. In some embodiments, the half width is in the range of 0.16°, 0.18°, 0.20°, 0.22°, 0.24°, 0.27°, or a combination of any two of these values. In some embodiments, the width at half maximum is 0.15° to 0.25°. The half-width of the above-mentioned peaks of the composite particles within the above-mentioned range indicates that the degree of lattice order of the composite particles is reduced, and the mixing between LiF and transition metal fluorides is more uniform.

According to some embodiments of the present application, the grain size of the composite particles is 30 nm to 100 nm, wherein the grain size is calculated by Scherrer formula. In some embodiments, the composite particles have a grain size of 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or a range consisting of any two of these values.

According to some embodiments of the present application, the transition metal includes at least one of Fe, Co, Ni, Mn or Cu. In some embodiments, the transition metal is Fe. In some embodiments, the transition metal is Co. In some embodiments, the transition metals are Fe and Co.

According to some embodiments of the present application, the transition metal fluoride is represented by the composition MF _y , wherein M is selected from one of transition metals, preferably selected from one of Fe, Co, Ni, Mn or Cu, 2 ≤y≤3.

According to some embodiments of the present application, the transition metal fluoride is represented by the composition M1 _y1 M2 _y2 F _y3 , wherein M1 and M2 are different, each independently selected from one of the transition metals, preferably selected from Fe, Co, Ni, Mn Or one of Cu, 2≤y ₃ /(y ₁ +y ₂ )≤3.

According to some embodiments of the present application, the transition metal fluoride includes at least one of FeF ₃ , CoF ₃ , Fe _0.9 Co _0.1 F ₃ , NiF 3 , MnF ₃ , FeF ₂ , CoF ₂ , NiF ₂ _or CuF ₂ .

2. Preparation method of cathode material

According to some embodiments of the present application, the molar ratio z of lithium fluoride and transition metal fluoride is 0.01, 0.02, 0.035, 0.04, 0.045, 0.055, 0.065, 0.07, 0.075, 0.085, 0.09, 0.095, 0.11, 0.12 or these A range of any two of the values. When the content of lithium fluoride is too low, the improvement of the performance of the electrochemical device is not obvious; It will reduce the discharge gram capacity of the positive electrode material.

In some embodiments, the molar ratio z of lithium fluoride and transition metal fluoride satisfies: 0.03≤z≤0.1. In some embodiments, the molar ratio x of lithium fluoride to transition metal fluoride in the composite particle satisfies: 0.05≤z≤0.08.

According to some embodiments of the present application, the mixing time is 1 h to 5 h, such as 2 h, 3 h or 4 h, etc. In some embodiments, the lithium fluoride and the transition metal fluoride can be mixed by mechanical mixing methods such as ball milling. In some embodiments, the rotational speed of the ball mill is 300r/min to 1000r/min, such as 400r/min, 500r/min, 600r/min or 800r/min.

According to some embodiments of the present application, the temperature of the above heat treatment is 200°C to 400°C. When the heat treatment temperature is too low, the atoms cannot overcome the diffusion barrier, and the diffusion is difficult to proceed, so the prepared positive electrode material exhibits poor electrochemical performance. When the heat treatment temperature is too high, on the one hand, the transition metal fluoride may react with the adsorbed oxygen on its surface or the air introduced by the tube furnace due to poor sealing, resulting in the formation of inert impurity phases. It is easy to decompose to generate low-valent metal fluorides, which will lead to the reduction of the electrochemical performance of the obtained positive electrode material.

In some embodiments, the temperature of the heat treatment is 220°C, 240°C, 260°C, 280°C, 310°C, 330°C, 350°C, 370°C, 390°C or any combination of these values. In some embodiments, the temperature of the heat treatment is 200°C to 350°C. In some embodiments, the temperature of the heat treatment is 250°C to 300°C.

According to some embodiments of the present application, the first mixture is heat-treated in an inert atmosphere. In some embodiments, the inert atmosphere is an argon atmosphere or a nitrogen atmosphere.

According to some embodiments of the present application, the heat treatment time is 6h to 24h, such as 7h, 10h, 15h or 20h and so on.

According to some embodiments of the present application, the transition metal is selected from at least one of Fe, Co, Ni, Mn or Cu. In some embodiments, the transition metal is Fe and/or Co.

According to some embodiments of the present application, the transition metal fluoride is represented by the composition MF _y , wherein M is selected from one of transition metals, preferably selected from one of Fe, Co, Ni, Mn or Cu, 2≤ y≤3.

The present application also provides the positive electrode material prepared by the above method, wherein the positive electrode material includes composite particles, and the composite particles include lithium fluoride and transition metal fluoride, wherein the molar ratio x of lithium fluoride and transition metal fluoride satisfies: 0 <x≤0.135.

According to some embodiments of the present application, the molar ratio x of lithium fluoride and transition metal fluoride in the composite particle is 0.01, 0.02, 0.035, 0.04, 0.045, 0.055, 0.065, 0.07, 0.075, 0.085, 0.09, 0.095, 0.11 , 0.12, or a range of any two of these values.

According to some embodiments of the present application, in the X-ray spectrum of the composite particles, there are peaks between 23° and 24° in 2θ, and the half width of the peaks is 0.15° to 0.3°. According to some embodiments of the present application, the grain size of the composite particles is 30 nm to 100 nm, wherein the grain size is calculated by Scherrer formula.

According to some embodiments of the present application, in the transition metal fluoride of the positive electrode material, the molar ratio y of the fluorine element to the transition metal element satisfies: 2≤y≤3.

According to some embodiments of the present application, the transition metal of the positive electrode material is selected from at least one of Fe, Co, Ni, Mn or Cu. In some embodiments, the transition metal is Fe. In some embodiments, the transition metal is Co. In some embodiments, the transition metals are Fe and Co.

According to some embodiments of the present application, the transition metal fluoride of the positive electrode material is represented by the composition MF _y , wherein M is selected from one of the transition metals, preferably selected from one of Fe, Co, Ni, Mn or Cu , 2≤y≤3.

According to some embodiments of the present application, the transition metal fluoride of the positive electrode material is represented by the composition M1 _y1 M2 _y2 F _y3 , wherein M1 and M2 are different, each independently selected from one of the transition metals, preferably independently selected from Fe, Co , Ni, Mn or Cu, 2≤y ₃ /(y ₁ +y ₂ )≤3.

According to some embodiments _of _the present application _, _the _transition metal _fluoride _of _the _positive _electrode material _includes at least A sort of.

3. Electrochemical device

The electrochemical device provided by the present application includes a positive electrode, and the positive electrode includes the positive electrode material described in the first aspect of the present application or the positive electrode material prepared by the preparation method described in the second aspect.

According to some embodiments of the present application, after the electrochemical device is fully charged, the positive electrode material includes LiF and MF _y , wherein, 2≤y≤3, and M includes at least one of transition metals. In some embodiments, the transition metal is selected from at least one of Fe, Co, Ni, Mn or Cu. In some embodiments, the transition metal is Fe. In some embodiments, the transition metal is Co. In some embodiments, the transition metals are Fe and Co. In some embodiments, after the electrochemical device is fully charged, the molar ratio X' of LiF and MF _y in the cathode material satisfies 0<X'≤0.135.

According to some embodiments of the present application, the positive electrode further includes a conductive agent and a binder. In some embodiments, binders include, but are not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-containing Oxygen polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or Nylon etc. In some embodiments, conductive agents include, but are not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

According to some embodiments of the present application, the positive electrode further includes a positive electrode current collector. In some embodiments, a metal foil or a composite current collector can be used as the positive electrode current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate.

The positive electrode of the present application can be prepared by methods known in the art. Usually, materials such as positive electrode materials and optional conductive agents (such as carbon materials such as carbon black and metal particles, etc.), binders (such as SBR), and other optional additives (such as PTC thermistor materials) are mixed together Disperse in a solvent (such as deionized water), stir evenly, and evenly coat on the positive electrode current collector, and dry to obtain the positive electrode containing the positive electrode membrane.

According to some embodiments of the present application, the electrochemical device further includes a negative electrode.

According to some embodiments of the present application, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector. In some embodiments, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material may include a material that reversibly intercalates/deintercalates lithium ions, lithium metal, lithium metal alloy, or transition metal oxide. In some embodiments, the negative active material includes at least one of carbon material or silicon material. The carbon material includes at least one of graphite and hard carbon, and the silicon material includes at least one of silicon, silicon oxide, silicon carbon or silicon alloy. In some embodiments, the negative active material layer includes a binder, and the binder may include various binder polymers. In some embodiments, the binder includes polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polypropylene ester, polyacrylic acid, polyacrylate salt, sodium carboxymethyl cellulose , polyvinylpyrrolidone, polyvinyl ether, polymethylmethacrylate, polytetrafluoroethylene, polyhexafluoropropylene or styrene-butadiene rubber. In some embodiments, the negative active material layer further includes a conductive material to improve electrode conductivity. Any conductive material can be used as the conductive material as long as it does not cause a chemical change. In some embodiments, the conductive material includes at least one of conductive carbon black, acetylene black, carbon nanotubes, Ketjen black, conductive graphite, or graphene.

According to some embodiments of the present application, the negative electrode is lithium metal or a lithium-containing alloy. In some embodiments, the negative electrode is a lithium sheet.

According to some embodiments of the present application, the electrochemical device further includes an electrolytic solution or a solid electrolyte.

According to some embodiments of the present application, the electrolyte that can be used in the examples of the present application can be the electrolyte known in the prior art.

In some embodiments, the electrolyte includes an organic solvent, a lithium salt, and additives. The organic solvent of the electrolytic solution according to the present application can be any organic solvent known in the prior art that can be used as a solvent for the electrolytic solution. The electrolyte used in the electrolytic solution according to the present application is not limited, and it may be any electrolyte known in the prior art. The additive of the electrolytic solution according to the present application may be any additive known in the prior art as an additive to the electrolytic solution. In some embodiments, the organic solvents include, but are not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate. In some embodiments, the organic solvent includes an ether solvent, for example, at least one of 1,3-dioxane (DOL) and ethylene glycol dimethyl ether (DME). In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salts include, but are not limited to: lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium difluorophosphate (LiPO ₂ F ₂ ), bistrifluoromethanesulfonylimide Lithium LiN(CF ₃ SO ₂ ) ₂ (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO ₂ F) ₂ )(LiFSI), lithium bisoxalate borate LiB(C ₂ O ₄ ) ₂ (LiBOB ) or lithium difluorooxalate borate LiBF ₂ (C ₂ O ₄ ) (LiDFOB).

According to some embodiments of the present application, the solid electrolyte includes Li _2+x Al _2+x Si _1-x S ₆ (0≤x<1), Li ₃ YCl ₆ , Li ₃ YBr ₆ , Li ₃ OCl, LiPON , Li _0.5 La _0.5 TiO ₃ , Li _1+x Al _x Ti _2-x (PO ₄ ) ₃ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₁₀ GeP ₂ S ₁₂ (LGPS), Li _9.54 Si _1.74 P _1.44 S At least one of _11.7 Cl _0.3 , Li _3.25 Ge _0.25 P _0.75 S ₄ , Li ₁₁ AlP ₂ S ₁₂ and Li ₇ P ₃ S ₁₁ .

According to some embodiments of the present application, in the electrochemical device, a separator is provided between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the isolation film used in the embodiments of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or an inorganic material formed of a material stable to the electrolyte of the present application. For example, a release film may include a substrate layer and a surface treatment layer. The substrate layer is non-woven fabric, film or composite film with a porous structure, and the material of the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite film can be selected. At least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. The inorganic layer includes inorganic particles and binders, and the inorganic particles include aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, oxide At least one of yttrium, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. Binders include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, poly At least one of methyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The polymer layer comprises a polymer, and the polymer material includes polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly( at least one of vinylidene fluoride-hexafluoropropylene).

According to some embodiments of the present application, the electrochemical device of the present application includes, but is not limited to: all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, lithium secondary batteries include, but are not limited to: lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries.

4. Electronic devices

The electronic device of the present application can be any device using the electrochemical device according to the third aspect of the present application.

In some embodiments, the electronic devices include, but are not limited to: notebook computers, pen-based computers, mobile computers, e-book players, cellular phones, portable fax machines, portable copiers, portable printers, stereo headsets , VCR, LCD TV, Portable Cleaner, Portable CD Player, Mini Disc, Transceiver, Electronic Notepad, Calculator, Memory Card, Portable Recorder, Radio, Backup Power, Motor, Automobile, Motorcycle, Assisted Bicycle, Bicycle , Lighting appliances, toys, game consoles, clocks, electric tools, flashlights, cameras, large household batteries or lithium-ion capacitors, etc.

Examples and comparative examples

Example 1

Weigh 2.966g (26.25mmol) of FeF ₃ raw material and 0.034g (1.31mmol) of LiF raw material respectively, stir well, put into 50mL agate jar, and then ball mill at 500r/min for 2h. Next, the obtained mixture material was placed in a tube furnace protected by an argon atmosphere, and the temperature was raised to 180° C. at a heating rate of 5° C./min for heat treatment, and the heat treatment time was 12 hours. After the heat treatment is completed, the material is naturally cooled to room temperature, and after crushing and sieving, a positive electrode material with a nominal composition of 0.05LiF.FeF ₃ is obtained.

Lithium secondary battery production: First, add the above-mentioned 0.05LiF.FeF ₃ positive electrode material, conductive agent (SP) and binder PVDF into N-methylpyrrolidone (NMP) according to the mass ratio of 60:30:10, and stir well The slurry is made into positive electrode slurry. The positive electrode slurry was evenly coated on the aluminum foil of the positive electrode current collector with a scraper, and then dried, cold pressed and punched to make positive electrode sheets. Finally, the positive electrode sheet was used as the positive electrode, the lithium sheet was used as the negative electrode, Cellgard 2400 was used as the separator, 4.6mol/L LiFSI and DME were used as the electrolyte, and a CR2430 button battery was assembled in an argon atmosphere glove box.

Example 2 to Example 5

The preparation of the positive electrode material and the manufacturing process of the button battery refer to Example 1, the difference is that in Example 2 to Example 5, the heat treatment temperatures during the preparation of the positive electrode material are 200°C, 300°C, 400°C and 430°C respectively.

Example 6

Weigh 2.979g (26.36mmol) of FeF ₃ raw material and 0.021g (0.81mmol) of LiF raw material respectively, stir well, put into 50mL agate jar, and then ball mill at 500r/min for 2h. Next, the obtained mixture material was placed in a tube furnace protected by an argon atmosphere, and the temperature was raised to 250° C. at a heating rate of 5° C./min for heat treatment, and the heat treatment time was 12 hours. After the heat treatment, the material was naturally cooled to room temperature, and after crushing and sieving, a positive electrode material with a nominal composition of 0.03LiF.FeF ₃ was obtained.

Reference Example 1 for the manufacture of a lithium secondary battery based on the above-mentioned 0.03LiF.FeF ₃ cathode material.

Example 7

Weighed 2.959g (26.19mmol) of _FeF3 raw material and 0.041g (1.58mmol) of LiF raw material respectively, and adopted the same experimental preparation steps as in Example 1 to obtain a positive electrode material with a nominal composition of _0.06LiF.FeF3 .

Reference Example 1 for the manufacture of a lithium secondary battery based on the above-mentioned 0.06LiF.FeF ₃ cathode material.

Example 8

Weighed 2.946g (26.07mmol) of _FeF3 raw material and 0.054g (2.08mmol) of LiF raw material respectively, and adopted the same experimental preparation steps as in Example 1 to obtain a positive electrode material with a nominal composition of _0.08LiF.FeF3 .

Reference Example 1 for the manufacture of a lithium secondary battery based on the above-mentioned 0.08LiF.FeF ₃ positive electrode material.

Example 9

Weighed 2.933g (25.96mmol) of _FeF3 raw material and 0.067g (2.59mmol) of LiF raw material respectively, and adopted the same experimental preparation steps as in Example 1 to obtain a positive electrode material with a nominal composition of _0.1LiF.FeF3 .

Reference Example 1 for the manufacture of a lithium secondary battery based on the above-mentioned 0.1LiF.FeF ₃ positive electrode material.

Example 10

Weighed 2.913g (25.78mmol) of _FeF3 raw material and 0.087g (3.36mmol) of LiF raw material respectively, and adopted the same experimental preparation steps as in Example 1 to obtain a positive electrode material with a nominal composition of _0.13LiF.FeF3 .

Reference Example 1 for the manufacture of a lithium secondary battery based on the above-mentioned 0.13LiF.FeF ₃ positive electrode material.

Example 11

Weigh 2.662g (23.56mmol) of FeF ₃ raw material, 0.304g (2.62mmol) of CoF ₃ raw material and 0.034g (1.31mmol) of LiF raw material, stir well, put into 50mL agate jar, and then ball mill at 500r/min 2h. Next, the obtained mixture material was placed in a tube furnace protected by an argon atmosphere, and the temperature was raised to 300° C. at a heating rate of 5° C./min for heat treatment, and the heat treatment time was 12 hours. After the heat treatment, the material was naturally cooled to room temperature, and after crushing and sieving, a positive electrode material with a nominal composition of 0.05LiF.Fe _0.9 Co _0.1 F ₃ was obtained.

Production of all-solid-state lithium secondary battery: Weigh the above-mentioned positive electrode material of 0.05LiF.Fe0.9Co0.1F ₃ , solid electrolyte Li10GeP ₂ S ₁₂ (LGPS) and conductive carbon (SP) according to the mass ratio of 4:5:1, and use Grinding in an agate mortar for more than 30 minutes to obtain a mixed powder of positive electrode materials. Next, 100mg Li ₁₀ GeP ₂ S ₁₂ (LGPS) and 50mg Li ₇ P ₃ S ₁₁ (LPS) were weighed and placed in a cold press mold to obtain a double-layer solid electrolyte membrane under a pressure of 240MPa. Then, put the mixed powder of the positive electrode material and the double-layer solid electrolyte into a stainless steel cold press mold, in which the mixed powder of the positive electrode material is placed on the LGPS layer, and cold-pressed under a pressure of 250MPa to obtain a sheet of positive electrode and solid electrolyte; One side of the LPS layer is put into a metal lithium sheet, and placed in a cold press mold together with the previous sheet, and a further 150MPa pressure is applied to make the interface of the positive electrode, solid electrolyte and metal lithium sheet fully contact, and fasten with screws to obtain a solid-state battery sample .

Example 12

Weigh respectively 2.632g (23.29mmol) of _FeF3 raw material, 0.300g (2.59mmol) of _CoF3 raw material and 0.067g (2.59mmol) of LiF3 raw material, and the rest adopt the same experimental preparation steps as in Example 11 to obtain a nominal composition of 0.1LiF . Fe _0.9 Co _0.1 F ₃ cathode material.

Reference Example 11 for making an all-solid lithium secondary battery based on the above-mentioned 0.1LiF.Fe _0.9 Co _0.1 F ₃ positive electrode material.

Example 13

Weigh 2.603g (23.04mmol) of _FeF3 raw material, 0.297g (2.56mmol) of _CoF3 raw material and 0.100g (3.86mmol) of LiF raw material respectively, and adopt the same experimental preparation steps as in Example 11 to obtain the nominal composition of 0.15LiF . Fe _0.9 Co _0.1 F ₃ cathode material.

Reference Example 11 for making an all-solid-state lithium secondary battery based on the above-mentioned 0.15LiF.Fe _0.9 Co _0.1 F ₃ positive electrode material.

Comparative example 1

Weigh 2.966g (26.25mmol) of _FeF3 raw material and 0.034g (1.31mmol) of LiF raw material respectively, put them into a 50mL agate jar, ball mill at 500r/min for 12h, and sieve to obtain a positive electrode with a nominal composition of _0.05LiF.FeF3 Material. Reference Example 1 for the manufacture of a lithium secondary battery based on the above-mentioned 0.05LiF.FeF ₃ material.

Comparative example 2

Weigh 3g of commercial FeF ₃ raw material, put it into a 50mL agate jar, and ball mill it at 500r/min for 2h to obtain small particles of FeF ₃ material.

Reference Example 1 for the manufacture of a lithium secondary battery based on the above-mentioned FeF ₃ material.

Comparative example 3

Weigh 3g of commercial FeF ₃ raw material, put it into a 50ml agate jar, and ball mill it at 500r/min for 2h. Next, the obtained mixture material was placed in a tube furnace protected by an argon atmosphere, and the temperature was raised to 250° C. at a heating rate of 5° C./min for heat treatment, and the heat treatment temperature was 12 hours. After the heat treatment is completed, the material is naturally cooled to room temperature, and after crushing and sieving, the heat-treated small particle FeF ₃ material is obtained.

Comparative example 4

Firstly, 3g of commercial FeF ₃ raw material was weighed, put into a 50mL agate jar, and ball milled at 500r/min for 12h to obtain small particles of FeF ₃ material. Then, the small particle FeF ₃ material, LiF raw material, conductive agent (SP), and binder PVDF are added to N-methylpyrrolidone (NMP) in a mass ratio of 58.9:1.1:30:10 and stirred to make a positive electrode. Slurry, and then use a scraper to evenly coat the positive electrode slurry on the aluminum foil of the positive electrode current collector, and finally dry, cold press and die-cut to make the positive electrode sheet. The amount of LiF relative to _FeF3 in the prepared positive pole piece is 0.08. Reference Example 1 for the manufacture of a lithium secondary battery using the above-mentioned positive electrode sheet as the positive electrode.

Comparative example 5

Weigh 2.69g (23.80mmol) of commercial _FeF3 raw material and 0.31g (2.68mmol) of _CoF3 raw material respectively, put them into a 50mL agate jar, and ball mill at 500r/min for 2h. Next, the obtained mixture material was placed in a tube furnace protected by an argon atmosphere, and the temperature was raised to 300° C. at a heating rate of 5° C./min for heat treatment, and the heat treatment temperature was 12 hours. After the heat treatment, the material was naturally cooled to room temperature, and after crushing and sieving, a positive electrode material with a nominal composition of Fe _0.9 Co _0.1 F ₃ was obtained.

Reference Example 11 for the production of an all-solid-state lithium secondary battery based on the aforementioned Fe _0.9 Co _0.1 F ₃ material.

Test Methods

1. Discharge gram capacity and cycle capacity retention test

(1) CR2430 button battery

After the CR2430 button cell was aged in a constant temperature room (25°C) for 24 hours, the initial activation was carried out at a charge-discharge current density of 25mA/g in the first cycle, and the charge-discharge current density was changed to 50mA/g in the second cycle and later. The gram capacity of the second cycle is used as the reference standard for cycle capacity decay, that is, the capacity retention rate of the nth cycle = the discharge capacity of the nth cycle / the discharge capacity of the second cycle × 100%. During the charging and discharging process, the lower limit of the discharge cut-off voltage is 1V, and the upper limit of the charge cut-off voltage is 4V.

(2) All-solid lithium secondary battery

After the all-solid-state lithium secondary battery is aged in a constant temperature room (25°C) for 24 hours, the initial activation is performed at a charge-discharge current density of 10mA/g in the first cycle, and the charge-discharge current density is changed to 25mA/g in the second cycle and later . The gram capacity of the second cycle is used as the reference standard for cycle capacity decay, that is, the capacity retention rate of the nth cycle = the discharge capacity of the nth cycle / the discharge capacity of the second cycle × 100%. During the charging and discharging process, the lower limit of the discharge cut-off voltage is 1V, and the upper limit of the charge cut-off voltage is 4V.

2. XRD test

X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE) was used to test the positive electrode material, the target material was Cu Kα; the voltage and current were 40KV/35mA, the scanning angle range was 10° to 60°, and the scanning rate was 5°/min.

3. Calculation of grain size

The grain size of the material is calculated by the Scherrer formula D=Kλ/βcosθ. Wherein, D is the grain size, K is the Scherrer constant (K=0.94), λ is the wavelength of Cu Kα ray, β is the half-peak width (radian unit), and θ is the Bragg angle of the X-ray diffraction peak.

4. SEM test

Scanning electron microscope characterization was recorded by a PhilipsXL-30 field emission scanning electron microscope and detected under the conditions of 10kV and 10mA.

5. Elemental composition test of cathode material

The elemental composition of the positive electrode material was tested. The content of Li, Fe, and Co elements was measured by Optima 7000DV inductively coupled plasma spectrometry (ICP) tester from American PE company, and the content of F element was measured by Thermo Fisher’s ion chromatography tester. Before the F element test, it is necessary to dissolve the positive electrode material to be tested with a certain amount of dilute nitric acid solution to completely form an F ^- aqueous solution, and then perform the test.

Test Results

Table 1 shows the effect of the heat treatment temperature on the performance of the obtained positive electrode material and the lithium ion battery comprising the positive electrode material.

Wherein, FeF ₃ and LiF were mixed by ball milling during the preparation process of the positive electrode materials of Comparative Example 1 and Example 1 to Example 5. The electrolytes in the lithium ion batteries of Comparative Example 1 and Example 1 to Example 5 are all LiFSI+DME, and the nominal composition of the initial positive electrode material is 0.05LiF.FeF ₃ .

Table 1

Comparative Example 1 and Examples 1 to 5 in Table 1 show the effects of heat treatment temperature on the gram capacity and cycle stability of the metal fluoride composite cathode material (ie, the cathode material of the present application). When only simple ball-milling composite treatment was performed, the discharge gram capacity of the positive electrode material in the second cycle and the capacity retention rate of the 20th cycle in Comparative Example 1 were both the lowest, which were 429.8mAh/g and 72.2%, respectively. When the heat treatment temperature is 180°C, the discharge gram capacity of the positive electrode material in the second cycle and the capacity retention rate in the 20th cycle of the positive electrode material in Example 1 are slightly improved compared with Comparative Example 1, but not significantly. As the heat treatment temperature increased to 300°C, the discharge gram capacity and capacity retention rate of the positive electrode material in Example 3 both reached the maximum, and compared with Comparative Example 1, they increased by 40.4mAh/g and 15.0%, respectively. When the heat treatment temperature is further increased to 400° C. and above, the discharge gram capacity and cycle stability of the positive electrode materials in Examples 4 and 5 both show a downward trend. When the heat treatment temperature is 430° C., the discharge gram capacity and capacity retention rate of the positive electrode material in Example 5 are at the same level as those of the positive electrode material in Comparative Example 1.

The above results show that the preferred heat treatment temperature in the preparation process of the positive electrode material of the present application is 200°C to 400°C. When the heat treatment temperature is too low, the atoms cannot overcome the diffusion barrier, and the diffusion is difficult, so the electrochemical performance of the material is not good. When the heat treatment temperature is too high, on the one hand, the transition metal fluoride may react with the adsorbed oxygen on the surface of the material or the air introduced by the tube furnace due to poor sealing, resulting in the formation of an inert impurity phase. It is easy to decompose and generate low-valent transition metal fluorides, which will lead to a decrease in the electrochemical performance of the material.

FIG. 1 shows the XRD test results of the positive electrode materials in Comparative Example 1 and Examples 1 to 5. When the heat treatment temperature is less than 200°C, the XRD spectra of the cathode material in Example 1 and the cathode material in Comparative Example 1 are very similar, and the main phase is FeF ₃ , while containing a very small amount of LiF. Due to the small amount of LiF compounded and the reduction of crystallinity caused by ball milling, its XRD diffraction peaks are not significant, which is consistent with the electrochemical performance of cathode materials.

When the heat treatment temperature is 200° C. to 400° C., compared with the positive electrode material in Comparative Example 1, the XRD of the positive electrode material in the corresponding example shows obvious differences. First, the half-width of the diffraction peak corresponding to the (101) crystal plane of FeF ₃ at around 23.8° appears to be significantly broadened, which may be related to the interdiffusion reaction between LiF and FeF ₃ materials. Among them, the corresponding half-peak width in Comparative Example 1 is 0.09°, and the grain size of the positive electrode material calculated according to the Scherrer formula is relatively large, about 117nm, while the corresponding half-peak widths in Examples 1 to 5 are 0.12° respectively. °, 0.2°, 0.22°, 0.25° and 0.26°, according to the Scherrer formula, the grain size of the material is calculated to be 88nm, 53nm, 48nm, 42nm and 40nm, respectively. The reaction kinetics of conversion-type metal fluoride cathode materials is poor, and the smaller the grain size, the more conducive to improving the reaction kinetics, thereby improving the electrochemical performance. Secondly, the intensity of the characteristic diffraction peaks of LiF (the (111) crystal plane corresponds to about 38.7° and the (200) crystal plane corresponds to about 45.0°) intensity gradually weakens with the increase of heat treatment temperature. The broadened diffraction peak means that the lattice order of the material is reduced, and the intensity of the LiF characteristic diffraction peak is reduced, which indicates that LiF and FeF ₃ undergo diffusion reactions during heat treatment. Further, when the temperature was raised above 400°C, the XRD spectrum of the positive electrode material in Example 5 also showed the diffraction peak of FeF ₂ (may correspond to the pyrolysis of FeF ₃ : FeF ₃ → FeF ₂ +F ₂ ), and at the same time Accompanied by other unknown weak phase diffraction peaks.

Table 1 also shows the element composition and phase composition of the positive electrode materials in Comparative Example 1 and Examples 1 to 5 in different states. It can be seen from Table 1 that for the initial cathode material, the actual measured elemental composition of the material is very close to the nominal composition of the material. With the increase of heat treatment temperature, the relative content of F elements decreased slightly, which was consistent with the XRD test results. During the high-temperature heat treatment process, a very small part of FeF ₃ decomposes to form FeF ₂ , resulting in a small amount of F element loss. Excessively high heat treatment temperature will lead to more loss of F element, which may affect the electrical properties of the material. After the battery is assembled and fully charged to 1V for the first time, the active materials in the positive electrode sheet are mainly LiF and Fe, which originate from the reaction process of FeF ₃ +Li→Fe+LiF. Since the initial LiF is in excess, the measured molar ratio of Li and F elements in the fully charged cathode material is slightly greater than 1, as expected. Furthermore, the molar ratio of LiF and Fe in the positive electrode sheet is greater than 3 after full discharge, which can ensure that the nano-Fe element can be completely transformed into metal fluoride during the subsequent charging process, which is more conducive to the development of battery capacity.

Table 2 shows that the molar ratio of LiF and transition metal fluoride in the positive electrode material affects the performance of the lithium ion battery of the positive electrode material.

Wherein, the electrolyte in the lithium ion batteries of Comparative Example 2 to Comparative Example 4 and Example 6 to Example 10 is LiFSI+DME.

Table 2

Comparative Examples 2 to 4 and Examples 6 to 10 in Table 2 show the relationship between the relative content of LiF in the positive electrode material and the discharge gram capacity and capacity retention. First of all, by comparing Comparative Example 2 and Comparative Example 3, it can be concluded that for transition metal fluoride cathode materials that do not contain lithium fluoride, the effect of heat treatment on the electrochemical performance of the material is basically negligible, so it can be ruled out that heat treatment has no effect on the electrochemical performance of the material. Influence of lithium fluoride on the electrochemical performance of transition metal fluoride cathode materials. Secondly, compared with Comparative Example 2, Comparative Example 4 directly added 0.08mol LiF in the positive electrode slurry preparation process, and the electrochemical performance of the battery after the material was made did not change significantly. The electrochemical performance of the material cannot be improved. Therefore, the key to improving the electrochemical performance of positive electrode materials lies in lithium fluoride, and heat treatment at an appropriate temperature is required. As mentioned above, the effect of heat treatment is to promote the compounding of materials more uniformly.

As shown in FIG. 3 , as the LiF content increases, the discharge gram capacity of the positive electrode materials in Comparative Example 2 and Examples 6 to 10 shows a trend of first increasing and then decreasing. When the amount of LiF relative to _FeF3 is 0.08, the discharge gram capacity of the positive electrode material in Example 8 reaches a maximum of 540.2mAh/g, and compared with Comparative Example 2, the improvement ratio reaches 25%. When the amount of LiF relative to _FeF3 is 0.13, the discharge gram capacity of the material in Example 10 has been reduced to 465.1 mAh/g. Since LiF does not provide a discharge gram capacity, and its intrinsic conductivity is extremely low, an excessively high addition ratio will sacrifice the discharge gram capacity of the positive electrode material. In addition, by comparing Example 6 and Comparative Example 2, it can be seen that by compounding LiF in the transition metal fluoride material, the cycle stability of the material is significantly improved. Specifically, when the recombination ratio of LiF is only 0.03mol, the discharge capacity retention rate of the cathode material in Example 6 at the 20th cycle is increased from 70.4% in Comparative Example 2 to 85.7%. With the increase of the relative content of LiF in the cathode material, the cycle stability of the cathode material has been further improved. When the amount of LiF relative to _FeF3 is 0.13, the cycle retention rate of the material in Example 10 is as high as 92.1%.

Figure 4 shows the comparison of the cyclic voltammetry curves of the second cycle and the fifth cycle of the battery in Example 10. The test voltage range is 1V to 4.2V, and the scan rate is 0.1mV/s. It can be seen that the two curves basically overlap. It further shows that the positive electrode material of the present application has extremely high cycle stability.

It is speculated that the mechanism for the significant improvement of the electrochemical performance of cathode materials by compounding LiF may be that the traditional conversion reaction metal fluoride cathode materials first generate nano-metal elemental particles and LiF during the discharge process. In the subsequent charging process, the nanometer metal element is oxidized into metal ions, and recombined with fluorine ions to form metal fluoride. Since nanomaterials are prone to segregation or agglomeration, there may not be enough fluorine ions around the metal ions generated by oxidation during the charging process to combine with them to form stable metal fluorides. Metal ions that have not been transformed into metal fluorides are easily dissolved into the electrolyte, and shuttled to the negative electrode to be reduced to metal dendrites, which not only causes the loss of positive active materials and rapidly decays the gram capacity of the battery, but also causes the metal dendrites to Piercing the separator causes a short circuit inside the battery and cyclic diving occurs. However, after the positive electrode material is compounded with a certain proportion of lithium fluoride, the fluorine ions are always kept in excess during the charging process, which can ensure that the metal ions are completely converted into stable metal fluorides, thereby avoiding a large amount of metal ions in the positive electrode. The high discharge specific capacity and high cycle stability of the material. Finally, by compounding LiF, no other impurity elements are introduced, which will not affect other performances of the battery. The introduced Li can also provide part of the active lithium, which can further improve the electrochemical stability.

Table 3 shows the test results of the positive electrode material of the present application in an all-solid-state battery.

Among them, the electrolyte in the lithium-ion batteries of Comparative Example 5 and Examples 11 to 13 is LGPS+LPS, the pretreatment method is ball milling, and the heat treatment temperature is 300°C.

table 3

Comparative Example 5 and Examples 11 to 13 in Table 3 show the test results of positive electrode materials in all-solid-state batteries. Compared with Comparative Example 5, it can be seen that when the ratio of composite LiF in the Fe _0.9 Co _0.1 F ₃ cathode material is less than or equal to 0.1, the discharge gram capacity and cycle stability of the material in the example are improved to varying degrees. However, when the recombination amount of LiF is further increased to about 0.15, the initial discharge gram capacity is too much lost despite its better cycle stability. Specifically, the positive electrode material in Example 13 has a capacity retention rate close to 93% after 20 cycles, but its initial discharge gram capacity has been reduced to about 420mAh/g, which is lower than the 443mAh/g of the material in Comparative Example 5. Similar to the above results, it shows that LiF itself does not provide the gram capacity, but excess will reduce the overall gram capacity of the material. In general, improving the electrochemical performance of conversion-type metal fluoride cathode materials by compounding a certain proportion of LiF has certain universal applicability.

While a few exemplary embodiments of the present application have been illustrated and described, the application is not limited to the disclosed embodiments. Rather, those of ordinary skill in the art will recognize that certain modifications and changes can be made to the described embodiments without departing from the spirit and scope of the application as described in the appended claims.

Claims

A positive electrode material comprising composite particles, the composite particles comprising lithium fluoride and transition metal fluoride, wherein the molar ratio x of the lithium fluoride to the transition metal fluoride satisfies: 0<x≤0.135.
The positive electrode material according to claim 1, wherein 0.025≤x≤0.11.
The positive electrode material according to claim 1, wherein, in the X-ray spectrum of the composite particles, there is a peak between 23° and 24° in 2θ, and the half-maximum width of the peak is 0.15° to 0.3°;

And/or the grain size of the composite particles is 30nm to 100nm, wherein the grain size is calculated by Scherrer formula.
The positive electrode material according to claim 1, wherein, in the transition metal fluoride, the molar ratio y of the fluorine element to the transition metal element satisfies: 2≤y≤3.
The positive electrode material according to claim 1, wherein the positive electrode material satisfies at least one of the following conditions (a) to (b):

(a) the transition metal comprises at least one of Fe, Co, Ni, Mn or Cu;

(b) The transition metal fluoride includes at least one of FeF 3 , CoF 3 , Fe 0.9 Co 0.1 F 3 , NiF 3 , MnF 3 , FeF 2 , CoF 2 , NiF 2 or CuF 2 .
A method for preparing a positive electrode material, comprising the following steps: mixing lithium fluoride and a transition metal fluoride to obtain a first mixture, wherein the molar ratio z of the lithium fluoride and transition metal fluoride satisfies: 0<z≤0.13 ; and heat-treating the first mixture.
The preparation method according to claim 6, wherein at least one of the following conditions (a) to (d) is satisfied:

(a) the transition metal comprises at least one of Fe, Co, Ni, Mn or Cu;

(b) the transition metal fluoride includes at least one of FeF 3 , CoF 3 , Fe 0.9 Co 0.1 F 3 , NiF 3 , MnF 3 , FeF 2 , CoF 2 , NiF 2 or CuF 2 ;

(c) The molar ratio z of the lithium fluoride to the transition metal fluoride satisfies: 0.03≤z≤0.1;

(d) The heat treatment temperature is 200°C to 400°C, and the heat treatment time is 6h to 24h.
An electrochemical device, comprising a positive electrode, the positive electrode comprising the positive electrode material according to any one of claims 1 to 5 or the positive electrode material prepared by the preparation method according to claim 6 or 7.
The electrochemical device according to claim 8, wherein, after the electrochemical device is fully charged, the positive electrode material comprises LiF and MF y , wherein, 2≤y≤3, M comprises at least one of transition metals.
An electronic device comprising the electrochemical device according to claim 8 or 9.