Positive electrode material, electrochemical apparatus, and electronic apparatus

Abstract

Provided are a positive electrode material, an electrochemical apparatus and an electronic apparatus. An electrode comprising the positive electrode material is assembled with lithium metal to form a button battery, and when the button battery is charged at a current of 0.04 C within a voltage range of 2.8 V to 4.5 V, the charging capacity per gram of the positive electrode material is greater than or equal to 215 mAh / g. The positive electrode material can improve the energy density of the electrochemical apparatus and enable the electrochemical apparatus to have excellent cycle performance and safety performance.

Description

Cathode material, electrochemical device and electronic device TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage, in particular to a cathode material, and an electrochemical device and an electronic device comprising the cathode material. BACKGROUND

[0002] With the gradual depletion of fossil energy, the demand for clean energy in society is increasing. In this process of transformation, lithium-ion batteries play a crucial role, and among them, ternary cathode materials are of great concern due to their low cost and high energy density characteristics, especially in the field of electric vehicles. In order to further improve the energy density of ternary cathode materials, scientists have endeavored to increase the content of nickel in the material and increase the working voltage of the battery. These methods can indeed improve the capacity of the battery, but at the same time, they also bring challenges in terms of safety. This is mainly because in the high delithiation state, the thermal stability of the ternary cathode material is poor, and oxygen release or reaction with the electrolyte to produce gas is easy to occur, thus leading to thermal runaway of the battery and posing a safety hazard. Therefore, while pursuing high energy density, ensuring the safety of the battery has become an important research topic.

[0003] SUMMARY

[0004] In view of the above problems existing in the prior art, the present application proposes a cathode material, an electrochemical device and an electronic device. By doping other elements in the lithium layer of the cathode material and controlling the synthesis method, the lithium layer and the internal oxygen defects of the material are regulated. Under the synergistic effect of the doping elements in the lithium layer and the internal oxygen defects, the lithium ions in the material can be fully removed, thereby greatly improving the utilization rate of lithium ions and the energy density of the material. At the same time, the interaction between oxygen and transition metals in the material is also greatly improved, stabilizing the oxygen structure in the material and inhibiting the phase transition from layered phase to spinel or rock salt phase, ultimately greatly reducing the gas production of the material under high temperature conditions and greatly improving the cycle stability.

[0005] In a first aspect, the present application proposes a cathode material. An electrode comprising the cathode material is assembled with a lithium metal into a coin cell. When the coin cell is charged at a current of 0.04C in a voltage interval of 2.8V to 4.5V, the charge gram capacity of the cathode material is greater than or equal to 215mAh / g.

[0006] In some embodiments, when the coin cell is charged at a current of 0.04C in a voltage interval of 2.8V to 4.5V, the charge gram capacity of the cathode material is 235mAh / g to 255mAh / g.

[0007] In some embodiments, the anode material has an exothermic peak with a peak intensity whose absolute value is less than or equal to 1.5 mW / mg based on the mass of the anode material.

[0008] In some embodiments, the anode material has an exothermic peak with a peak intensity whose absolute value is less than or equal to 1.5 mW / mg based on the mass of the anode material.

[0009] In some embodiments, the anode material has a weight loss rate of less than or equal to 30% at 800°C when the button cell is charged to 4.5V at a current of 0.04C.

[0010] In some embodiments, the button cell has a first oxidation peak and a first reduction peak in a 4.2V to 4.4V range when the button cell is charged and discharged at a current of 0.04C in a 2.8V to 4.5V voltage range.

[0011] In some embodiments, the first oxidation peak has a peak voltage Vo1, the first reduction peak has a peak voltage Vr1, and |Vo1-Vr1|≤0.2V.

[0012] In some embodiments, the second oxidation peak has a peak voltage Vo2, the second reduction peak has a peak voltage Vr2, and |Vo2-Vr2|≤0.3V.

[0013] In some embodiments, the button cell has a discharge curve with a platform in a 4.2V to 4.5V range in a voltage-capacity curve obtained when the button cell is charged and discharged at a current of 0.04C in a 2.8V to 4.5V voltage range, the capacity of the discharge curve in the 4.2V to 4.5V range is Q1, and the capacity of the discharge curve in a 3.0V to 4.5V range is Qt, satisfying: 0.1≤Q1 / Qt≤0.35.

[0014] In some embodiments, the anode material has an X-ray diffraction pattern with diffraction peaks in a 17° to 19°, 35.5° to 38.5°, and 43° to 45° range.

[0015] In some embodiments, the positive electrode material comprises a lithium transition metal composite oxide comprising elements T and optionally elements Q, the elements T comprising at least one of Ni, Co or Mn, the elements Q comprising at least one of K, Ca, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, La, Ce, Hf, Ta, W, Pb, Al, Mg, B, Si, P, S, Ti, V, Cr, Fe, Cu, Zn, Ga or Ge.

[0016] In some embodiments, the molar percentage content of Ni is 30% to 70% based on the total molar amount of the elements T.

[0017] In some embodiments, the molar percentage content of Mn is 0% to 70% based on the total molar amount of the elements T.

[0018] In some embodiments, the molar percentage content of Co is 0% to 70% based on the total molar amount of the elements T.

[0019] In some embodiments, the lithium transition metal composite oxide further comprises Na element, the molar percentage content of the Na element is 0.1% to 10% based on the total molar amount of the elements T and elements Q.

[0020] In some embodiments, the molar percentage content of the elements Q is 0% to 10% based on the total molar amount of the elements T and elements Q.

[0021] In some embodiments, the lithium transition metal composite oxide further comprises elements M1, M1 comprising at least one of F, Cl, Br, I or N; the molar percentage content of the elements M1 is 0.1% to 10% based on the total molar amount of the elements T and elements Q.

[0022] In some embodiments, the lithium transition metal composite oxide, the ratio of the molar amount of Li element to the total molar amount of the elements T and elements Q is 0.5 to 1.1.

[0023] In some embodiments, the lithium transition metal composite oxide has a layered crystal structure belonging to the R-3m space group.

[0024] In some embodiments, the lithium transition metal composite oxide comprises Li x1 Na x2 Ni y1 Mn y2 Co y3 Q z1 O 2±m M1 m0.6≤x1≤1.2, 0.001≤x2≤0.1, 0.3≤y1≤0.7, 0.3≤y2≤0.7, 0.3≤y3≤0.7, 0≤z1≤0.1, 0≤m≤0.2, wherein element Q comprises at least one of K, Ca, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, La, Ce, Hf, Ta, W, Pb, Al, Mg, B, Si, P, S, Ti, V, Cr, Fe, Cu, Zn, Ga or Ge, and element M1 comprises at least one of F, Cl, Br, I or N.

[0025] In a second aspect, the present application also provides an electrochemical device comprising a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode material of the first aspect.

[0026] In some embodiments, the electrochemical device further comprises an electrolyte, wherein the electrolyte comprises an additive, and the additive comprises at least one of a sulfur-oxygen double bond-containing compound or a polynitrile compound.

[0027] In some embodiments, the sulfur-oxygen double bond-containing compound comprises one or more of 1,3-propane sultone, ethylene sulfate, 2,4-butane sultone, 1,4-butane sultone, methane disulfonic acid methylene ester, 1,3-propane disulfonic acid anhydride, 4-methyl ethylene sulfate or pentaerythritol bicyclic sulfate.

[0028] In some embodiments, the mass percentage of the sulfur-oxygen double bond-containing compound is 0.1% to 5% based on the mass of the electrolyte.

[0029] In some embodiments, the polynitrile compound comprises at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelonitrile, methylglutaronitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3,5-pentanetricarbonitrile, 1,3,6-hexanetricarbonitrile or 1,2,3-tris(2-cyanoethoxy)propane.

[0030] In some embodiments, the mass percentage of the polynitrile compound is 1% to 10% based on the mass of the electrolyte.

[0031] In a third aspect, the present application provides an electronic device comprising the electrochemical device of the second aspect. BRIEF DESCRIPTION OF DRAWINGS

[0032] The drawings necessary for describing the embodiments of the present application or the prior art will be briefly described hereinafter. Obviously, the drawings in the following description are only some of the embodiments in the present application. Other drawings of embodiments can also be obtained by those skilled in the art according to these drawings.

[0033] Figure 1 is an XRD pattern of the positive electrode material powder of Comparative Example 1 and Example 10.

[0034] Figure 2 is a voltage capacity curve of the button cell of Comparative Example 1 and Example 10.

[0035] Figure 3 is a capacity voltage differential dQ / dV curve of the button cell of Comparative Example 1 and Example 10. DETAILED DESCRIPTION

[0036] For the purpose of clarity, technical solutions and advantages of the present application will be described below in detail with embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as a limitation of the present application.

[0037] For the purpose of clarity, technical solutions and advantages of the present application will be described below in detail with embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as a limitation of the present application.

[0038] In the description herein, unless otherwise specified, "above", "below" include the number. Unless otherwise specified, the terms used in the present application have the commonly understood meanings by those skilled in the art. Unless otherwise specified, 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 method given in the examples of the present application).

[0039] In the detailed description and in the claims, a list of items connected by the term "at least one of" "at least one of" "at least one of" or other similar terms means 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 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 can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0040] In a first aspect, the application provides a positive electrode material. When an electrode comprising the positive electrode material and a lithium metal are assembled into a button cell, and the button cell is charged at a current of 0.04C in a voltage range of 2.8V to 4.5V, the positive electrode material has a charge specific capacity greater than or equal to 215mAh / g.

[0041] By doping other elements in the lithium layer and controlling the synthesis method, the application can realize the regulation of the lithium layer and the internal oxygen defects of the material. Under the synergistic effect of the doping elements in the lithium layer and the internal oxygen defects, the lithium ions in the material can be fully extracted, thereby greatly improving the utilization rate of lithium ions and the energy density of the material. At the same time, the interaction between oxygen and transition metals in the material is also greatly improved, on the one hand, the oxygen structure in the material can be stabilized, and on the other hand, the phase transition from layered phase to spinel or rock salt phase can be inhibited. Finally, the gas production of the material under high temperature conditions is greatly reduced, and the cycle stability is greatly improved.

[0042] In some embodiments, when the button cell is charged to 4.5V at a current of 0.04C, the positive electrode material has an exothermic peak with the strongest peak in the range of 240°C to 290°C within the range of 45°C to 450°C, tested by a differential scanning calorimeter. In this way, the positive electrode material has high structural stability in the charged state, thereby improving the high-temperature storage and cycle performance of the positive electrode material. Specifically, the positive electrode material has an exothermic peak with the strongest peak at 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, or within a range consisting of any two of these values.

[0043] In some embodiments, the absolute value of the peak intensity of the strongest peak of the exothermic peak of the positive electrode material is less than or equal to 1.5mW / mg based on the mass of the positive electrode material. Specifically, the absolute value of the peak intensity of the strongest peak can be 0.8mW / mg, 0.9mW / mg, 1.0mW / mg, 1.1mW / mg, 1.2mW / mg, 1.3mW / mg, 1.4mW / mg, 1.5mW / mg, or within a range consisting of any two of these values.

[0044] In some embodiments, when the button cell is charged to 4.5V at a current of 0.04C, the positive electrode material has a weight loss rate of less than or equal to 30% at 800°C.

[0045] In some embodiments, the capacity-voltage differential dQ / dV curve obtained when the button cell is charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V has a first oxidation peak and a first reduction peak in a range of 4.2V to 4.4V. This indicates that the positive electrode material has reversible charge and discharge capacity in a high voltage range of 4.2V to 4.5V, thereby making the positive electrode material have a high energy density and good structural stability.

[0046] In some embodiments, the first oxidation peak has a peak voltage Vo1, the first reduction peak has a peak voltage Vr1, and |Vo1-Vr1|≤0.2V. In some embodiments, |Vo1-Vr1| can be 0.2V, 0.18V, 0.16V, 0.14V, 0.12V, 0.1V, 0.08V, 0.06V, 0.04V, 0.02V, 0.01V, or a range consisting of any two of these values.

[0047] In some embodiments, the capacity-voltage differential dQ / dV curve obtained when the button cell is charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V has a second oxidation peak and a second reduction peak in a range of 3.6V to 3.9V.

[0048] In some embodiments, the second oxidation peak has a peak voltage Vo2, the second reduction peak has a peak voltage Vr2, and |Vo2-Vr2|≤0.3V. In some embodiments, |Vo2-Vr2| can be 0.3V, 0.28V, 0.26V, 0.24V, 0.22V, 0.2V, 0.18V, 0.16V, 0.14V, 0.12V, 0.1V, 0.08V, 0.06V, 0.04V, 0.02V, 0.01V, or a range consisting of any two of these values.

[0049] In some embodiments, the discharge curve in the voltage-capacity curve obtained when the button cell is charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V has a plateau in a range of 4.2V to 4.5V. This indicates that the positive electrode material can have reversible discharge capacity in a high voltage range of 4.2V to 4.5V.

[0050] In some embodiments, when the button cell is charged and discharged at a current of 0.04C in a voltage range of 2.8V to 4.5V, the capacity in the discharge curve in the voltage capacity curve obtained is Q1 in the range of 4.2V to 4.5V, and the capacity of the discharge curve is Qt in the range of 3.0V to 4.5V, and 0.1≤Q1 / Qt≤0.35 is satisfied. At this time, the capacity of the positive electrode material in the high voltage range of 4.2V to 4.5V is high, so that the positive electrode material has a higher energy density. In some embodiments, Q1 / Qt can be 0.1, 0.12, 0.14, 0.15, 0.2, 0.25, 0.3, 0.35, or a range consisting of any two of these values.

[0051] In some embodiments, the X-ray diffraction pattern of the positive electrode material has diffraction peaks in the ranges of 17° to 19°, 35.5° to 38.5°, and 43° to 45°.

[0052] In some embodiments, the positive electrode material comprises a lithium transition metal composite oxide comprising element T, wherein the element T comprises at least one of Ni, Co, or Mn, and optionally element Q, wherein the element Q comprises at least one of K, Ca, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, La, Ce, Hf, Ta, W, Pb, Al, Mg, B, Si, P, S, Ti, V, Cr, Fe, Cu, Zn, Ga, or Ge.

[0053] In some embodiments, the molar percentage content of Ni is 30% to 70% based on the total molar amount of the element T. In some embodiments, the molar percentage content of Ni in the lithium transition metal oxide is 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or a range consisting of any two of these values, based on the total molar amount of the T element in the lithium transition metal oxide.

[0054] In some embodiments, the molar percentage content of Mn is 0% to 70% based on the total molar amount of the element T. For example, 0%, 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, or a range consisting of any two of these values.

[0055] In some embodiments, the molar percentage content of Co is 0% to 70% based on the total molar amount of the element T. For example, 0%, 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, or a range consisting of any two of these values.

[0056] In some embodiments, the lithium transition metal composite oxide further comprises Na element, the molar percentage content of the Na element is 0.1% to 10% based on the total molar amount of the element T and the element Q. For example, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two of these values.

[0057] In some embodiments, the molar percentage content of the element Q is 0 to 10% based on the total molar amount of the element T and the element Q. For example, 0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10% or a range consisting of any two of these values.

[0058] In some embodiments, the lithium transition metal composite oxide further comprises element M1, M1 comprises at least one of F, Cl, Br, I or N; the molar percentage content of the element M1 is 0.1% to 10% based on the total molar amount of the element T and the element Q. For example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1%, 2%, 3%, 4%, 5%, 8%, 10% or a range consisting of any two of these values.

[0059] In some embodiments, the ratio of the molar amount of the element Li to the total molar amount of the element T and the element Q in the lithium transition metal composite oxide is 0.5 to 1.1. For example, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1 or a range consisting of any two of these values.

[0060] In some embodiments, the lithium transition metal composite oxide has a layered crystal structure belonging to the R-3m space group.

[0061] In some embodiments, the lithium transition metal composite oxide comprises Li x1 Na x2 Ni y1 Mn y2 Co y3 Q z1 O 2±m M1 m0.6 < x1 < 1.2, 0.001 < x2 < 0.1, 0.3 < y1 < 0.7, 0.3 < y2 < 0.7, 0.3 < y3 < 0.7, 0 < z1 < 0.1, 0 < m < 0.2, wherein the element Q comprises at least one of K, Ca, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, La, Ce, Hf, Ta, W, Pb, Al, Mg, B, Si, P, S, Ti, V, Cr, Fe, Cu, Zn, Ga, or Ge, and the element M1 comprises at least one of F, Cl, Br, I, or N.

[0062] In a second aspect, the present application also provides an electrochemical device, which comprises a positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer comprising the positive electrode material of the first aspect.

[0063] In some embodiments, the positive electrode active material layer further comprises a conductive agent and a binder. In some embodiments, the binder comprises, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, or vinylidene fluoride-hexafluoropropylene copolymer, etc. In some embodiments, the conductive agent comprises, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based materials are selected from carbon black, acetylene black, ketjen black, carbon nanotubes, carbon fibers, graphene, or any combination thereof. In some embodiments, the metal-based materials are selected from metal powders or metal fibers. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0064] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, an 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.

[0065] The electrochemical device of the present application also comprises a negative electrode, which comprises a negative electrode active material layer and a negative electrode current collector.

[0066] In some embodiments, the negative active material layer includes a negative active material, a binder, and optionally a conductive agent. In some embodiments, the negative active material includes at least one of a carbon material or a silicon material. In some embodiments, the carbon material includes at least one of graphite, hard carbon, or soft carbon. In some embodiments, the silicon material includes at least one of silicon, a silicon oxide compound, a silicon carbon compound, or a silicon alloy. In some embodiments, the binder includes at least one of a polyamide, a polyacrylonitrile, an acrylate polymer, a polyacrylic acid, a polyacrylic acid salt, sodium carboxymethyl cellulose, a polyvinylpyrrolidone, a polyvinyl ether, or a styrene butadiene rubber. In some embodiments, the conductive agent can use any conductive material as long as it does not cause chemical changes. In some embodiments, the conductive agent includes at least one of a conductive carbon black, acetylene black, a carbon nanotube, a ketjen black, a carbon fiber, or graphene.

[0067] In some embodiments, the negative current collector can be a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0068] In some embodiments, the electrochemical device further includes an electrolyte, and the electrolyte includes an additive, and the additive includes at least one of a sulfur-oxygen double bond-containing compound or a polynitrile compound. The sulfur-oxygen double bond-containing compound can form an oxidation-resistant protective film on the surface of the positive active material, and the rich S element can stabilize the high-valence transition metal in the charged state, thereby better inhibiting the release of oxygen on the surface of the positive active material and the oxidative decomposition of the electrolyte. The polynitrile compound can complex with the transition metal on the surface of the positive active material, stabilize the transition metals such as nickel, cobalt, and manganese on the surface of the positive active material, and inhibit the release of oxygen on the surface of the positive active material, thereby improving the high-temperature storage performance and cycle performance of the electrochemical device.

[0069] In some embodiments, the sulfur-oxygen double bond-containing compound includes one or more of 1,3-propane sultone, ethylene sulfate, 2,4-butane sultone, 1,4-butane sultone, methane disulfonic acid methylene ester, 1,3-propane disulfonic anhydride, 4-methyl ethylene sulfate, or pentaerythritol bicyclic sulfate.

[0070] In some embodiments, the mass percentage of the sulfur-oxygen double bond-containing compound is 0.1% to 5% based on the mass of the electrolyte. For example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1%, 2%, 3%, 4%, 5%, or a range between any two of these values.

[0071] In some embodiments, the multi-carbonyl compound comprises at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelonitrile, methylglutaronitrile, 1,2-di(2-cyanoethoxy)ethane, 1,3,5-pentanetriconitrile, 1,3,6-hexanetrione, or 1,2,3-tri(2-cyanoethoxy)propane.

[0072] In some embodiments, the multi-carbonyl compound has a mass percentage of 1% to 10% based on the mass of the electrolyte. For example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range between any two of these values.

[0073] In some embodiments, the electrolyte further comprises a lithium salt and a nonaqueous solvent.

[0074] In some embodiments, the lithium salt is selected from one or more of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate. For example, the lithium salt can be LiPF6.

[0075] In some embodiments, the nonaqueous solvent can be a carbonate compound, a carboxylic ester compound, an ether compound, or a combination thereof. The carbonate compound can be a chain carbonate compound, a cyclic carbonate compound, or a combination thereof. Examples of the chain carbonate compound are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and a combination thereof. Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and a combination thereof. Examples of the carboxylic ester compound are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, caprolactone, and a combination thereof. Examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and a combination thereof.

[0076] According to some embodiments of the present application, a separator is provided between the positive electrode and the negative electrode to prevent short circuiting. The material and shape of the separator used in the embodiments of the present application are not particularly limited and can be any of the techniques disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance formed of a material stable to the electrolyte of the present application, and the like. For example, the separator can include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. A surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed of a mixture of a polymer and an inorganic substance. The inorganic layer includes inorganic particles and a binder, and the inorganic particles include at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder includes at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene, or polyhexafluoropropylene. The polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or vinylidene fluoride-hexafluoropropylene copolymer.

[0077] According to some embodiments of the present application, the electrochemical device of the present application includes, but is not limited to, a primary battery or a secondary battery of all kinds. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0078] In a third aspect, the electronic device of the present application can be any device using the electrochemical device of the second aspect of the present application.

[0079] In some embodiments, the electronic device includes, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic notebook, a calculator, a memory card, a portable audio recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery, or a lithium ion capacitor, etc.

[0080] Examples and Comparative Examples

[0081] Hereinafter, the present application will be further described by citing examples and comparative examples, and it is to be understood that the present application is not limited to these examples.

[0082] 1. Preparation of the positive electrode material

[0083] Comparative Example 1

[0084] Step 1: A mixed solution containing NiSO4and MnSO4was prepared according to the element molar ratio Ni:Mn=50:50, and was mixed with a precipitating agent (NaOH solution) and a complexing agent (ammonia water) for reaction, with the reaction time controlled to 60 hours, the ammonia water concentration controlled to 1 mol / L, and the PH controlled to 12.2, to obtain a nickel-manganese precursor TM(OH)2(TM=Ni / Mn) with an average particle size Dv50 of 11 um. 0.5 Mn 0.5 (OH)2;

[0085] Step 2: The precursor in Step 1 above and lithium carbonate were ground and mixed uniformly according to the molar ratio Li:element T (Ni / Mn) of 1.02:1, and were calcined at 800°C in an air atmosphere for 20h, with the temperature decreased to room temperature at a rate of 10°C / min, and finally crushed and sieved to obtain the positive electrode material.

[0086] Example 1

[0087] Step 1: A mixed solution containing NiSO4and MnSO4was prepared according to the element molar ratio Ni:Mn=50:50, and was mixed with a precipitating agent (NaOH solution) and a complexing agent (ammonia water) for reaction, with the reaction time controlled to 60 hours, the ammonia water concentration controlled to 1 mol / L, and the PH controlled to 12.2, to obtain a nickel-manganese precursor TM(OH)2(TM=Ni / Mn) with an average particle size Dv50 of 11 um.

[0088] Step 2, the nickel-manganese precursor in step 1 above and sodium carbonate were mixed uniformly in a ratio of (Ni+Mn) : Na = 1 : 1.05 (molar ratio), calcined in a dry air atmosphere at 800℃ for 20h, cooled to room temperature at a rate shown in Table 2 and passed into a first atmosphere (see Table 2 for specific composition), crushed and sieved to obtain a first product;

[0089] Step 3, the first product obtained in step 2 was mixed with a lithium source (a mixture of lithium hydroxide and lithium nitrate in a molar ratio of 1 : 1) (elemental molar ratio Li : elemental T = 7 : 1), then heated to 370℃ at a rate of 10℃ / min in a second atmosphere (mixed gas of Ar and air in a volume ratio of 1 : 2) and kept at this temperature for 6h, cooled to room temperature at a rate of 30℃ / min; finally washed with deionized water, dried, sieved to obtain a positive electrode material.

[0090] Examples 2-5

[0091] The difference from Example 1 is that the proportion and cooling rate of the first atmosphere in step 2 are changed.

[0092] Examples 6-9

[0093] The difference from Example 1 is that strontium hydroxide octahydrate is added to the precursor mixture in step 2, and the molar ratio of Sr to (Sr+elemental T (Ni / Mn)) in Examples 6-9 is 0.005 : 1, 0.01 : 1, 0.015 : 1 and 0.02 : 1 respectively.

[0094] Examples 10-11

[0095] The difference from Example 1 is that nano-titanium dioxide is added to the precursor mixture in step 2, and the molar ratio of Ti to (Ti+elemental T (Ni / Mn)) in Examples 10-11 is 0.01 : 1 and 0.02 : 1 respectively.

[0096] Examples 12-13

[0097] The difference from Example 1 is that nano-zirconium dioxide is added to the precursor mixture in step 2, and the molar ratio of Zr to (Zr+elemental T (Ni / Mn)) in Examples 12-13 is 0.01 : 1 and 0.02 : 1 respectively.

[0098] Examples 14-16

[0099] The difference from Example 1 is that zinc oxide is added to the precursor mixture in step 2, and the molar ratio of Zn to (Zn+elemental T (Ni / Mn)) in Examples 14-16 is 0.01 : 1, 0.02 : 1 and 0.03 : 1 respectively.

[0100] Examples 17-18

[0101] The difference from Example 1 is that tin dioxide is added to the precursor mixture in Step 2, and the molar ratio of Sn to (Sn + elemental T (Ni / Mn)) in Examples 17-18 is 0.01:1 and 0.02:1, respectively.

[0102] 2. Preparation of lithium ion battery

[0103] (1) Preparation of lithium ion button cell

[0104] A certain weight ratio of 5:5:90 of binder polyvinylidene fluoride (PVDF), conductive agent conductive carbon black (Super P) and positive electrode material is mixed, N-methyl pyrrolidone (NMP) is added and mixed uniformly, and a positive electrode slurry with a solid content of 0.7 is prepared. The mixed positive electrode slurry is uniformly coated on an aluminum foil with a coating thickness of 40 μm, and a single-sided coating is performed; after drying, it is rolled to form the required electrode, wherein the electrode coating area density is 14 mg / cm 2 , and after drying, a positive electrode sheet is obtained, which is punched into a 14 mm round sheet to obtain a single-sided positive electrode sheet. The separator film is punched into an 18 mm round sheet; the negative electrode used is a lithium metal sheet with a diameter of 18 mm; LiPF6 is added to a mixture of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (weight ratio 1:1:1) to obtain an electrolyte, wherein the mass concentration of LiPF6 is 12.5%. The positive electrode sheet, separator paper, negative electrode sheet (lithium sheet), electrolyte, and battery shell accessories are moved into a glove box (water content should be less than 11 ppm); the battery is assembled in the order of bottom to top and injected with electrolyte: negative shell > flat pad + appropriate amount of electrolyte > metal lithium sheet + appropriate amount of electrolyte > one layer of separator paper + appropriate amount of electrolyte > positive electrode sheet + appropriate amount of electrolyte > flat pad + appropriate amount of electrolyte > spring > positive shell; package on a packaging machine to obtain a button cell.

[0105] (2) Preparation of lithium ion soft package battery

[0106] Preparation of positive electrode

[0107] A certain weight ratio of 2:2:96 of binder polyvinylidene fluoride (PVDF), conductive agent conductive carbon black (Super P) and positive electrode material is mixed, N-methyl pyrrolidone (NMP) is added and mixed uniformly, and a positive electrode slurry with a solid content of 0.7 is prepared; the positive electrode slurry is uniformly coated on one side of the aluminum foil, and after drying, the above steps are repeated on the other side of the aluminum foil to obtain a double-sided coated positive electrode sheet; after cold pressing, cutting and welding of the tabs, the required positive electrode is obtained.

[0108] Preparation of negative electrode

[0109] The artificial graphite, styrene-butadiene rubber and sodium carboxymethyl cellulose (CMC) are mixed with deionized water in a mass ratio of 96:2:2, and stirred uniformly to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on one side surface of a copper foil, and after drying, the above-mentioned step is repeated on the other side surface of the copper foil to obtain a double-sided coated negative electrode sheet; after cold pressing, cutting and welding of the tabs, the required negative electrode is obtained.

[0110] Preparation of electrolyte

[0111] In a dry argon environment, LiPF6 is added and uniformly mixed in a solvent mixed from propylene carbonate (PC), ethylene carbonate (EC) and diethyl carbonate (DEC) (weight ratio 1:1:1) to obtain an electrolyte, wherein the mass concentration of LiPF6 is 12.5%.

[0112] Preparation of separator film

[0113] A porous polyethylene (PE) polymer film is used as the separator film.

[0114] Preparation of lithium ion soft package battery

[0115] The positive electrode, the separator film and the negative electrode are stacked in order, with the separator film between the positive electrode and the negative electrode to play a separating role, and the bare battery is obtained by winding. The bare battery is placed in an outer packaging aluminum plastic film, electrolyte is injected, and the lithium ion soft package battery is obtained after packaging, formation, degassing, edge cutting and other process flows.

[0116] Examples 19-38

[0117] The difference from Example 1 is that on the basis of Example 1, an additive (containing a sulfur-oxygen double bond compound and / or a polynitrile compound) is further added to the electrolyte, and the types and contents of the additives in each example and the performance of the corresponding lithium ion battery are shown in Table 2.

[0118] Test method

[0119] 1. Thickness expansion rate test at 85℃

[0120] The lithium ion soft package battery is charged at 1.5C rate to 4.35V at 85℃, and then charged at constant voltage to 0.05C at 4.35V to make the lithium ion battery reach full charge state. After 12h storage at 85℃, the thickness change of the lithium ion soft package battery is measured with a micrometer. The thickness before storage is defined as H0, the thickness after storage is defined as H1, and the thickness expansion rate is (H1-H0) / H0x100%.

[0121] 2. Cycle capacity retention rate test at 45℃

[0122] The lithium ion soft package battery is placed in a 45℃ constant temperature oven, and charged at a current of 1.5C to 4.35V, then charged at 4.35V until the current is 0.05C, and then discharged at a current of 4C to 3.0V, which is one charge-discharge cycle. The lithium ion battery is charged and discharged according to the above method for 300 cycles, and the discharge capacity of the first cycle and the discharge capacity of the 300th cycle of the lithium ion battery are recorded. The cycle capacity retention rate = discharge capacity of the 300th cycle / discharge capacity of the first cycle x 100%.

[0123] 3. XRD test

[0124] The anode material is tested by an X-ray powder diffractometer (instrument model: Bruker D8 ADVANCE, target material is Cu Kα; voltage and current are 40KV / 40mA, and the scanning angle range is 10° to 70°) to obtain the X-ray diffraction pattern of the anode material.

[0125] 4. Test method of the strongest exothermic peak position and peak intensity

[0126] The lithium ion button cell is charged at a current of 0.04C to 4.5V in the voltage range of 2.8V to 4.5V, and the anode sheet is obtained by disassembly. The anode sheet is cleaned with dimethyl carbonate (DMC), and then tested by a differential scanning calorimeter (instrument model: STA449F3, atmosphere: N2, heating rate is 10℃ / min).

[0127] 5. Test method of weight loss rate

[0128] The lithium ion button cell is charged at a current of 0.04C to 4.5V in the voltage range of 2.8V to 4.5V, and the anode sheet is obtained by disassembly. The anode sheet is cleaned with dimethyl carbonate (DMC), and then tested by a thermal gravimetric analyzer (instrument model: STA449F3-QMS403C, atmosphere: N2, heating rate is 10℃ / min) to obtain the weight loss rate of the charged anode material at 800℃.

[0129] 6. Test of charge gram capacity, capacity voltage differential dQ / dV curve, Q1 / Qt

[0130] The lithium ion button cell was charged at a current of 0.04 C to 4.5 V in a voltage range of 2.8 V to 4.5 V at an ambient temperature of 25°C, and then subjected to 4.5 V constant voltage charging until the current was 50 uA, and the charge capacity of the lithium ion button cell was recorded. Then, constant current discharge was performed at a current of 0.04 C until the lower limit voltage was 2.8 V, and the capacity-voltage curve and the capacity-voltage differential dQ / dV curve were recorded. The capacity Q1 in the voltage range of 4.2 to 4.5 V and the capacity Qt in the voltage range of 3.0 V to 4.5 V can be obtained according to the capacity-voltage curve. The charge gram capacity of the positive electrode material = the charge capacity of the lithium ion button cell / the mass of the positive electrode material.

[0131] Table 1 shows the composition of the positive electrode material, the composition of the first atmosphere and the cooling rate in step 2, and the parameters and performance of the corresponding positive electrode material in Comparative Example 1 and Examples 1-18.

[0132] Table 2

[0133] As can be seen from the comparison of Examples 1-18 and Comparative Example 1 in Table 1, the positive electrode material of the examples has a significantly improved charge gram capacity, and the high-temperature storage thickness expansion rate of the corresponding lithium ion soft package battery is greatly reduced, and the high-temperature cycle capacity retention rate is greatly improved. The possible reason is that, by doping Na element in the lithium layer of the positive electrode material and controlling the synthesis method, the lithium layer and the internal oxygen defects of the material are regulated, and under the synergistic effect of the doping element in the lithium layer and the internal oxygen defects, the lithium ions in the material can be fully removed, thereby greatly improving the utilization rate of lithium ions. And the existence of lithium layer doping elements and internal oxygen defects greatly improves the structural stability of the positive electrode material in the high delithiation state, inhibits the release of oxygen on the surface of the positive electrode material and the decomposition of the electrolyte, thereby improving the safety performance of the lithium ion battery.

[0134] As can be seen from the comparison of Examples 19-38 and Example 1 in Table 2, by further adding a sulfur-oxygen double bond containing compound and / or a multi-nitrile compound in the electrolyte, the high-temperature storage performance and high-temperature cycle performance of the lithium ion battery can be further improved. The possible reason is that the sulfur-oxygen double bond containing compound can form an oxidation resistant protective film on the surface of the positive electrode material, and the rich S element can stabilize the high valence transition metal in the charged state, thereby better inhibiting the release of oxygen on the surface of the positive electrode material and the oxidative decomposition of the electrolyte. The multi-nitrile compound can complex with the transition metal on the surface of the positive electrode active material, stabilize the transition metals such as nickel, cobalt and manganese on the surface of the positive electrode material, and inhibit the release of oxygen on the surface of the positive electrode material, thereby improving the high-temperature storage performance and cycle performance of the lithium ion battery.

[0135] While the illustrative embodiments have been described and illustrated, it will be understood by those skilled in the art that the above-described embodiments are not the only ways in which the present application can be practiced. Changes can be made to the embodiments in light of the teachings of the present disclosure, and it is understood that many variations and modifications can be made within the scope of the present application.

Claims

1. A positive electrode material, a button cell is assembled by assembling an electrode comprising the positive electrode material and lithium metal, when the button cell is charged in a voltage interval of 2.8 V to 4.5 V at a current of 0.04 C, the charge specific capacity of the positive electrode material is greater than or equal to 215 mAh / g.

2. The positive electrode material of claim 1, wherein, The positive electrode material satisfies at least one of the following conditions: (1) when the button cell is charged to 4.5 V at a current of 0.04 C, the strongest peak of the exothermic peak of the positive electrode material is in the range of 240°C to 290°C within the range of 45°C to 450°C, tested using a differential scanning calorimeter; (2) when the button cell is charged to 4.5 V at a current of 0.04 C, the weight loss rate of the positive electrode material at 800°C is less than or equal to 30%.

3. The positive electrode material of claim 2, wherein, The absolute value of the peak intensity of the strongest peak of the exothermic peak of the positive electrode material is less than or equal to 1.5 mW / mg based on the mass of the positive electrode material.

4. The cathode material of claim 1, wherein, When the button cell is charged and discharged in a voltage interval of 2.8 V to 4.5 V at a current of 0.04 C, the obtained capacity-voltage differential dQ / dV curve has a first oxidation peak and a first reduction peak in the interval of 4.2 V to 4.4 V; the capacity-voltage differential dQ / dV curve has a second oxidation peak and a second reduction peak in the interval of 3.6 V to 3.9 V.

5. The cathode material of claim 4, wherein, The positive electrode material satisfies at least one of the following conditions: (i) the peak voltage of the first oxidation peak is Vo1, the peak voltage of the first reduction peak is Vr1, and |Vo1-Vr1|≤0.2 V; (ii) the peak voltage of the second oxidation peak is Vo2, the peak voltage of the second reduction peak is Vr2, and |Vo2-Vr2|≤0.3 V.

6. The cathode material of claim 1, wherein, When the button cell is charged and discharged in a voltage interval of 2.8 V to 4.5 V at a current of 0.04 C, the discharge curve in the voltage capacity curve obtained has a platform in the interval of 4.2 V to 4.5 V, the capacity of the discharge curve in the interval of 4.2 V to 4.5 V is Q1, and the capacity of the discharge curve in the interval of 3.0 V to 4.5 V is Qt, satisfying: 0.1≤Q1 / Qt≤0.

35.

7. The cathode material of claim 1, wherein, The X-ray diffraction pattern of the positive electrode material has diffraction peaks in the intervals of 17° to 19°, 35.5° to 38.5°, and 43° to 45°.

8. The cathode material according to any one of claims 1 to 7, wherein, The positive electrode material comprises a lithium transition metal composite oxide, the lithium transition metal composite oxide comprises an element T and optionally an element Q, the element T comprises at least one of Ni, Co or Mn, the element Q comprises at least one of K, Ca, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, La, Ce, Hf, Ta, W, Pb, Al, Mg, B, Si, P, S, Ti, V, Cr, Fe, Cu, Zn, Ga or Ge; the lithium transition metal composite oxide satisfies at least one of the following conditions: (1) the molar percentage content of Ni is 30% to 70% based on the total molar amount of the element T; (2) the molar percentage content of Mn is 0% to 70% based on the total molar amount of the element T; (3) the molar percentage content of Co is 0% to 70% based on the total molar amount of the elements T; (4) the lithium transition metal composite oxide further comprises a Na element, the molar percentage content of the Na element is 0.1% to 10% based on the total molar amount of the elements T and the elements Q; (5) the molar percentage content of the elements Q is 0% to 10% based on the total molar amount of the elements T and the elements Q; (6) the lithium transition metal composite oxide further comprises an element M1, M1 comprises at least one of F, Cl, Br, I or N; the molar percentage content of the element M1 is 0.1% to 10% based on the total molar amount of the elements T and the elements Q; (7) the ratio of the molar amount of the Li element to the total molar amount of the elements T and the elements Q in the lithium transition metal composite oxide is 0.5 to 1.1; (8) the lithium transition metal composite oxide has a layered crystal structure belonging to the R-3m space group; (9) the lithium transition metal complex oxide includes Li x1 Na x2 Ni y1 Mn y2 Co y3 Q z1 O 2±m M1 m , 0.6≤x1≤1.2, 0.001≤x2≤0.1, 0.3≤y1≤0.7, 0.3≤y2≤0.7, 0.3≤y3≤0.7, 0≤z1≤0.1, 0≤m≤0.2, wherein the element M1 includes at least one of F, Cl, Br, I, or N.

9. An electrochemical device comprising a positive electrode sheet, the positive electrode sheet comprising the positive electrode material according to any one of claims 1 to 8.

10. The electrochemical device of claim 9, wherein, The electrochemical device further comprises an electrolyte, the electrolyte comprising an additive, the additive comprising at least one of a sulfur-oxygen double bond-containing compound or a polynitrile compound, the electrolyte satisfying at least one of the following conditions: (1) the sulfur-oxygen double bond-containing compound comprises one or more of 1,3-propane sultone, ethylene sulfate, 2,4-butane sultone, 1,4-butane sultone, methane dimesylate, 1,3-propane disulfonic anhydride, 4-methyl ethylene sulfate or pentaerythritol bicyclic sulfate; (2) the mass percentage content of the sulfur-oxygen double bond-containing compound is 0.1% to 5% based on the mass of the electrolyte; (3) the polynitrile compound comprises at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, melononitrile, methylglutaronitrile, 1,2-di(2-cyanoethoxy)ethane, 1,3,5-pentanetricarbonitrile, 1,3,6-hexanetricarbonitrile or 1,2,3-tri(2-cyanoethoxy)propane; (4) the mass percentage content of the polynitrile compound is 1% to 10% based on the mass of the electrolyte.

11. An electronic device comprising the electrochemical device of claim 9 or 10.

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