Positive electrode material, electrochemical device, and electronic device

Abstract

The application relates to a positive electrode material, an electrochemical device and an electronic device, an electrode comprising the positive electrode material is assembled into a button cell with a lithium sheet, when the button cell is charged at a current of 0.1 C in a range of 2.8 V to 4.4 V to 4.4 V, the charged gram capacity of the positive electrode material is greater than or equal to 220 mAh / g based on the weight of the positive electrode material, and the cell volume change rate Delta V1 of the positive electrode material is 7% to 11%. The positive electrode material of the application can have excellent structural stability while having a higher charged gram capacity, thereby improving the floating performance and high-temperature storage performance of the electrochemical device.

Description

TECHNICAL FIELD

[0001] 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

[0002] With the popularity of consumer electronics such as notebook computers, mobile phones, tablet computers, mobile power sources and unmanned aerial vehicles, the requirements for the batteries therein are becoming higher and higher. For example, not only is it required that the battery be light, but it is also required that the battery have high capacity and a long working life. Lithium ion batteries have occupied a dominant position in the market due to their outstanding advantages of high energy density, good safety, no memory effect and long working life.

[0003] In order to pursue higher energy density, lithium ion batteries have been developing in the direction of increasing voltage and increasing delithiation amount. Under high voltage and high delithiation amount, the problems of oxygen release and structure phase transition on the surface of the positive electrode material are fully exposed, bringing a series of problems such as battery cycle diving and gas production. On the other hand, the poor kinetics of ternary materials limits the capacity of the materials and causes the battery to have a serious temperature rise, which brings safety hazards. SUMMARY

[0004] Therefore, in a first aspect, the present application provides a positive electrode material. An electrode comprising the positive electrode material is assembled with a lithium sheet into a button cell. When the button cell is charged at a current of 0.1C to 4.4V in the range of 2.8V to 4.4V, the charge specific capacity of the positive electrode material is greater than or equal to 220mAh / g based on the weight of the positive electrode material, and the unit cell volume change rate AV1 of the positive electrode material is 7% to 11%.

[0005] Generally, the capacity of the positive electrode ternary material is mainly generated by the variable valence of nickel and cobalt. The capacity of the positive electrode material is related to the content of nickel contained in the positive electrode material. The higher the content of nickel, the higher the capacity of the positive electrode material. The Mn in the positive electrode material is in a +4 valence state, which does not provide capacity and further limits the energy density of the material. At the same time, the low electrochemical activity of manganese leads to poor kinetics of the material. Under deep delithiation, the surface oxygen ion of the material is highly active, which is easy to cause side reactions with the electrolyte, leading to an increase in interfacial impedance or gas production. In addition, when the lithium-oxygen layer spacing in the ternary material is low, it will hinder the diffusion of lithium ions at the end of discharge, leading to a delay in the kinetics of the material and an increase in the temperature rise of the battery.

[0006] The inventors of the present application found that element doping in the lithium layer by synthetic means can regulate the oxygen defects in the material and the lithium-oxygen layer spacing. The introduction of oxygen defects in the material can activate the redox properties of transition metals, greatly improving the energy density of the material. On the other hand, the oxygen vacancies formed on the surface can reduce the activity of the surface oxygen of the material, stabilize the outer layer oxygen ions of the material, and inhibit the oxygen release of the positive electrode material during floating and high-temperature storage. At the same time, doping high ionic radius elements in the lithium layer increases the lithium-oxygen layer spacing, increases the change rate of the unit cell parameter during lithium ion deintercalation, and can promote the full deintercalation of lithium ions and improve the kinetic performance of the material.

[0007] Therefore, the positive electrode material with the unit cell change rate ΔV1 according to the present application and the capacity of greater than or equal to 220 mAh / g according to the present application can bring higher energy density and improved kinetic performance to the electrochemical device.

[0008] According to some embodiments of the present application, the electrode comprising the positive electrode material is assembled with a lithium sheet into a button cell, and when the button cell is charged at a constant current of 0.1C to 4.0V in the range of 2.8V to 4.4V, the unit cell volume change rate ΔV2 of the positive electrode material is less than or equal to 3.5%. In this way, the unit cell volume change rate of the positive electrode material of the present application in the low voltage range is small, so that the positive electrode material has more excellent structural stability, and the floating performance and high-temperature storage performance of the electrochemical device can be improved.

[0009] According to some embodiments of the present application, the unit cell parameter a of the positive electrode material satisfies:

[0010] According to some embodiments of the present application, the unit cell parameter c of the positive electrode material satisfies: In this way, the positive electrode material of the present application has an increased lithium-oxygen layer spacing, so that the full deintercalation of lithium ions can be promoted and the kinetic performance of the material can be improved.

[0011] According to some embodiments of the present application, the unit cell volume v of the positive electrode material satisfies:

[0012] According to some embodiments of the present application, when the button cell is charged at a constant current of 0.1C to 4.4V in the range of 2.8V to 4.4V, the oxygen release initiation temperature of the positive electrode material is greater than or equal to 220°C. The oxygen vacancies formed in the interior and on the surface of the positive electrode material of the present application reduce the activity of oxygen in the material, and the element doping in the lithium layer inhibits the structural collapse of the material in the high delithiation state, so that the oxygen release of the positive electrode material can be inhibited, and the structural stability of the positive electrode material at high temperature and high voltage can be improved.

[0013] According to some embodiments of the present application, the electrode comprising the positive electrode material is assembled into a coin cell with lithium sheet, and the coin cell has a first oxidation peak and a first reduction peak in the capacity-voltage differential dQ / dV curve obtained when the coin cell is charged and discharged at a current of 0.1C in a voltage interval of 2.8V to 4.4V.

[0014] According to some embodiments of the present application, the capacity-voltage differential dQ / dV curve obtained has a second oxidation peak and a second reduction peak in the interval of 3.5V to 4.0V.

[0015] According to some embodiments of the present application, the positive electrode material comprises a lithium transition metal composite oxide, which comprises element T and optionally element M, the element T comprises at least one of Ni, Co or Mn, and the element M 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.

[0016] According to some embodiments of the present application, the mole percentage content of Ni is 30% to 70% based on the total mole amount of the element T. According to some embodiments of the present application, the mole percentage content of Mn is 0% to 70% based on the total mole amount of the element T. According to some embodiments of the present application, the mole percentage content of Co is 0% to 50% based on the total mole amount of the element T.

[0017] According to some embodiments of the present application, the mole percentage content of the element T is 90% to 100% and the mole percentage content of the element M is 0% to 10% based on the total mole amount of the element T and the element M.

[0018] According to some embodiments of the present application, the lithium transition metal composite oxide further comprises element R, the element R comprises at least one of F, Cl, Br, I or N, and the mole percentage content of the element R is 0.1% to 10% based on the total mole amount of the element T and the element M.

[0019] According to some embodiments of the present application, the ratio of the mole amount of Li element to the total mole amount of the element T and the element M in the lithium transition metal composite oxide is 0.5 to 1.1.

[0020] According to some embodiments of the present application, the lithium transition metal composite oxide further comprises Na element, and the mole percentage content of the Na element is 0.1% to 20% based on the total mole amount of the element T and the element M.

[0021] According to some embodiments of the present application, the lithium transition metal composite oxide has a layered crystal structure.

[0022] According to some embodiments of the present application, the lithium transition metal composite oxide comprises Li x1 Na x2 Ni y1 Mn y2 Co y3 M z1 O 2±m R m , 0.5≤x1≤1.1, 0.001≤x2≤0.2, 0.3≤y1≤0.7, 0≤y2≤0.7, 0≤y3≤0.5, 0≤z1≤0.1, 0≤m≤0.1, wherein the element R comprises at least one of F, Cl, Br, I or N.

[0023] In a second aspect, the present application provides an electrochemical device, comprising a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode material according to the first aspect of the present application.

[0024] According to some embodiments of the present application, 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. 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 polynitrile 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 structural stability of the positive electrode material at high temperature and high voltage.

[0025] According to some embodiments of the present application, the sulfur-oxygen double bond-containing compound comprises at least one of 1,3-propane sulfone, ethylene sulfate, 2,4-butane sulfone, 1,4-butane sulfone, methane disulfonic acid methylene ester, 1,3-propane disulfonic anhydride, 4-methyl ethylene sulfate or pentaerythritol bis-cyclic sulfate.

[0026] According to some embodiments of the present application, the mass percentage of the sulfur-oxygen double bond-containing compound in the electrolyte is 0.1% to 5% based on the mass of the electrolyte.

[0027] According to some embodiments of the present application, the polynitrile compound comprises at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelonitrile, methylglutaronitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3,5-pentanetrimethyl cyanide, 1,3,6-hexanetrimethyl cyanide or 1,2,3-tris(2-cyanoethoxy)propane.

[0028] According to some embodiments of the present application, the mass percentage of the polycarbonitrile compound is 0.5% to 10% based on the mass of the electrolyte.

[0029] In a third aspect, the present application provides an electronic device comprising the electrochemical device of the second aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The relationship of the cell volume versus the gravimetric capacity is shown for Example 7, Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0031] For the purpose of clarity, technical solutions and advantages of the present application will be further described below in conjunction with embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, and not 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 limiting the present application.

[0032] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with any other lower limit to form a range not explicitly recited, and likewise any upper limit can be combined with any other upper limit to form a range not explicitly recited. Further, each individual disclosed point or singular value can be combined with any other point or singular value to form a range not explicitly recited, either as a lower limit or an upper limit, or both.

[0033] In the description herein, unless otherwise stated, "above", "below" include the number itself.

[0034] Unless otherwise defined, the terms used in the present application have the meanings commonly understood by those skilled in the art. Unless otherwise stated, the values of each parameter 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).

[0035] The list of items connected by “at least one of,” “at least one,” “at least one of the,” or other similar phrases can mean any combination of the listed items. For example, if 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 A, B, and C are listed, the phrase “at least one of A, B, and C” means A alone; B alone; C alone; A and B (excluding C); A and C (excluding B); B and C (excluding A); or A, B, and C. Item A can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0036] I. Cathode material

[0037] In a first aspect, the present application provides a cathode, an electrode comprising the cathode material is assembled with lithium sheet into a button cell, when the button cell is charged at a current of 0.1C to 4.4V in the range of 2.8V to 4.4V, the charge specific capacity of the cathode material is greater than or equal to 220mAh / g, for example 220mAh / g, 230mAh / g, 240mAh / g, 250mAh / g, 260mAh / g, 270mAh / g, 280mAh / g, 290mAh / g, 300mAh / g, 310mAh / g, 320mAh / g, 330mAh / g or any range consisting of any of them based on the weight of the cathode material, and the cell volume change rate ΔV1 of the cathode material is 7% to 11%, for example ΔV1 is 7.0%, 7.2%, 7.4%, 7.6%, 7.8%, 8.0%, 8.2%, 8.4%, 8.6%, 8.8%, 9.0%, 9.2%, 9.4%, 9.6%, 9.8%, 10.0%, 10.2%, 10.4%, 10.6%, 10.8%, 11.0% or any range consisting of any of them.

[0038] In the present application, the cell volume change rate AV1 is obtained by the following method: for the synthesized initial positive electrode material, X-ray powder diffraction (XRD, instrument model: Bruker D8 ADVANCE, target Cu Ka; voltage and current are 40KV / 40mA, the scanning angle range is 10° to 70°) is used for testing; and the XRD results are fitted according to the Retiveld fitting method, and the cell parameters a, c and the cell volume V are obtained by the fitting results; the synthesized initial positive electrode material is assembled with lithium sheet into a button cell, and the button cell is charged at a current of 0.1C in the range of 2.8V to 4.4V to a specified voltage (for example 4.0V or 4.4V), and the positive electrode sheet is obtained by disassembling, and is cleaned by soaking in dimethyl carbonate (DMC), and after drying, the above-mentioned XRD test is carried out, and the XRD results are fitted according to the Retiveld fitting method, and the cell volume V' is obtained by the fitting results. The cell volume change rate AV=(V'-V) / Vx100%. And for the positive electrode material in the full battery, the difference is that the full battery is fully discharged first, and the positive electrode sheet is obtained by disassembling, and is cleaned by soaking in dimethyl carbonate (DMC), and after drying, the above-mentioned XRD test is carried out, and the cell parameters a, c and the cell volume V are obtained.

[0039] The inventors of the present application found that by means of synthesis, element doping in the lithium layer can regulate the internal oxygen defects and the lithium-oxygen layer spacing. The introduction of oxygen defects in the material can activate the redox properties of transition metals, greatly improving the energy density of the material. On the other hand, the oxygen vacancies formed on the surface can reduce the activity of the surface oxygen of the material, stabilize the outer layer oxygen ions of the material, and inhibit the oxygen release and gas production of the positive electrode material during floating and high-temperature storage. At the same time, doping elements with high ionic radius in the lithium layer increases the lithium-oxygen layer spacing, increases the change rate of the cell parameters during lithium ion deintercalation, and can promote the full deintercalation of lithium ions and improve the kinetic performance of the material.

[0040] In some embodiments, the electrode comprising the cathode material is assembled into a button cell with lithium sheet, and the button cell is charged at a current of 0.1 C to 4.0 V in a voltage range of 2.8 V to 4.4 V, the cell volume change rate AV2 of the cathode material is less than or equal to 3.5%, for example, AV2 is 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, or any range formed by any two of them. In this way, the cell volume change rate of the cathode material of the present application in the low voltage range is small, so that the cathode material has more excellent structure stability, and the float performance and high temperature storage performance of the electrochemical device can be improved.

[0041] In some embodiments, the lattice parameter a of the cathode material satisfies: For example, a is or any range formed by any two of them. According to some embodiments of the present application, the lattice parameter c of the cathode material satisfies: For example, c is or any range formed by any two of them. According to some embodiments of the present application, the lattice volume V of the cathode material satisfies: For example, V can be or any range formed by any two of them.

[0042] In some embodiments, the button cell is charged at a current of 0.1 C to 4.4 V in a voltage range of 2.8 V to 4.4 V, the oxygen release onset temperature of the cathode material is greater than or equal to 220°C, for example, it can be 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, or any range formed by any two of them. The oxygen vacancies formed inside and on the surface of the cathode material of the present application reduce the activity of oxygen in the material, and the element doping in the lithium layer inhibits the structural collapse of the material in the high delithiation state, thereby inhibiting the oxygen release of the cathode material and improving the structural stability of the cathode material at high temperature and high voltage.

[0043] In some embodiments, the electrode comprising the cathode material is assembled into a button cell with lithium sheet, and the button cell is charged and discharged at a current of 0.1 C in a voltage range of 2.8 V to 4.4 V, the obtained capacity voltage differential dQ / dV curve has a first oxidation peak and a first reduction peak in the range of 4.2 V to 4.4 V.

[0044] In some embodiments, the obtained capacity voltage differential dQ / dV curve has a second oxidation peak and a second reduction peak in the interval of 3.5 V to 4.0 V.

[0045] In some embodiments, the positive electrode material comprises a lithium transition metal composite oxide, the lithium transition metal composite oxide comprising an element T and optionally an element M, the element T comprising at least one of Ni, Co or Mn, the element M 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.

[0046] In some embodiments, the molar percentage content of Ni is 30% to 70%, for example 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or any interval constituted by any of them, based on the total molar amount of the element T. According to some embodiments of the present application, the molar percentage content of Mn is 0% to 70%, for example 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or any interval constituted by any of them, based on the total molar amount of the element T. According to some embodiments of the present application, the molar percentage content of Co is 0% to 50%, for example 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any interval constituted by any of them, based on the total molar amount of the element T.

[0047] In some embodiments, the molar percentage content of the element T is 90% to 100%, for example 90%, 91%, 94%, 96%, 98%, 99%, 100% or any interval constituted by any of them, and the molar percentage content of the element M is 0% to 10%, for example 0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any interval constituted by any of them, based on the total molar amount of the element T and the element M.

[0048] In some embodiments, the lithium transition metal composite oxide further comprises an element R, the element R comprising at least one of F, Cl, Br, I or N, the molar percentage content of the element R being 0.1% to 10%, for example 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any interval constituted by any of them, based on the total molar amount of the element T and the element M.

[0049] In some embodiments, the lithium transition metal composite oxide has a ratio of the molar amount of Li element to the total molar amount of the element T and the element M is 0.5 to 1.1, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, or any interval formed by any of them.

[0050] In some embodiments, the lithium transition metal composite oxide further comprises Na element, and the molar percentage content of the Na element is 0.1% to 20% based on the total molar amount of the element T and the element M, for example, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any interval formed by any of them.

[0051] In some embodiments, the lithium transition metal composite oxide has a layered crystal structure.

[0052] In some embodiments, the lithium transition metal composite oxide comprises Li x1 Na x2 Ni y1 Mn y2 Co y3 M z1 O 2±m R m , 0.5≤x1≤1.1, 0.001≤x2≤0.2, 0.3≤y1≤0.7, 0≤y2≤0.7, 0≤y3≤0.5, 0≤z1≤0.1, 0≤m≤0.1, wherein the element R comprises at least one of F, Cl, Br, I, or N.

[0053] II. Electrochemical device

[0054] The electrochemical device provided in the present application comprises a positive electrode comprising the positive electrode material of the first aspect of the present application.

[0055] According to some embodiments of the present application, the positive electrode 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 fluoride, polytetrafluoroethylene, polyvinylidene fluoride, or vinylidene-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 material is selected from carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube, graphene, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder or metal fiber. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0056] According to some embodiments of the present application, the positive electrode further comprises a positive electrode current collector. 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 on a polymer substrate.

[0057] According to some embodiments of the present application, the electrochemical device further comprises a negative electrode.

[0058] According to some embodiments of the present application, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer disposed on a surface of the negative electrode current collector. In some embodiments, the negative electrode active material layer comprises a negative electrode active material. In some embodiments, the negative electrode active material comprises at least one of a carbon material or a silicon material. The carbon material comprises at least one of graphite or hard carbon, and the silicon material comprises at least one of silicon, silicon oxide, silicon carbide, or silicon alloy. In some embodiments, the negative electrode active material layer comprises a binder. In some embodiments, the binder comprises at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, sodium carboxymethyl cellulose, polyvinylpyrrolidone, or styrene butadiene rubber. In some embodiments, the negative electrode active material layer further comprises a conductive material to improve the conductivity of the electrode. In some embodiments, the conductive material comprises at least one of conductive carbon black, acetylene black, carbon nanotube, ketjen black, or graphene.

[0059] According to some embodiments of the present application, the electrochemical device further comprises an electrolyte or a solid-state electrolyte.

[0060] According to some embodiments of the present application, the electrolyte that can be used in the embodiments of the present application can be an electrolyte known in the art.

[0061] In some embodiments, the electrolyte comprises an organic solvent, a lithium salt, and an additive. In some embodiments, the organic solvent comprises, but is 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 lithium salt comprises at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt comprises, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis-trifluoromethanesulfonimide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalato)borate LiB(C2O4)2 (LiBOB), or lithium difluoro(oxalato)borate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive comprises at least one of a sulfur-oxygen double bond-containing compound or a polynitrile compound.

[0062] In some embodiments, the sulfur-oxygen double bond containing compound includes at least one 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 bis cyclic sulfate. In some embodiments, the mass percentage of the sulfur-oxygen double bond containing compound is 0.1% to 5%, such as 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or any range constituted by the numbers, based on the mass of the electrolyte. In some embodiments, the polycarbonitrile compound includes at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelonitrile, methylglutaronitrile, 1,2-di(2-cyanoethoxy)ethane, 1,3,5-pentanetricarbonitrile, 1,3,6-hexanetricarbonitrile, or 1,2,3-tri(2-cyanoethoxy)propane. In some embodiments, the mass percentage of the polycarbonitrile compound is 0.5% to 10%, such as 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, or any range constituted by the numbers, based on the mass of the electrolyte.

[0063] 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 base layer and a surface treatment layer. The base layer is a non-woven fabric, a film, or a composite film having a porous structure, and the material of the base layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven 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 base 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, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, a polyacrylic acid salt, polyvinylpyrrolidone, a polyvinyl ether, polytetrafluoroethylene, or polyhexafluoropropylene. The polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, a polyacrylic acid salt, polyvinylpyrrolidone, a polyvinyl ether, polyvinylidene fluoride, or a copolymer of vinylidene fluoride-hexafluoropropylene.

[0064] 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.

[0065] III. Electronic device

[0066] The electronic device of the present application can be any device using the electrochemical device according to the second aspect of the present application.

[0067] 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 head-mounted stereo 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 recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a timepiece, an electric tool, a flashlight, a camera, a household large storage battery, or a lithium ion capacitor, etc.

[0068] Examples and Comparative Examples

[0069] Example 1

[0070] Preparation of a positive electrode material

[0071] (1) A mixed solution containing NiSO4and MnSO4was prepared according to the element molar ratio Ni:Mn=50:50, and the mixed solution was mixed with a precipitant (NaOH solution) and a complexing agent (ammonia water) to react, 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 T(OH)2(T represents Ni / Mn) with an average particle size Dv50 of 11 μm;

[0072] (2) The nickel-manganese precursor and sodium carbonate were mixed according to the molar ratio (Ni+Mn):Na of 1:1.05, and were calcined at 800°C in an air atmosphere for 20 hours, and then were crushed, sieved, and demagnetized to obtain a first product;

[0073] (3) The first product and a lithium source (a mixture composed of lithium hydroxide and lithium nitrate according to the molar ratio 1:1) were mixed, with the mass ratio of the lithium source to the first product being 10:1, and were heated to 400°C at a rate of 10°C / min, and were maintained for 14 hours, and were then quenched to room temperature in a mixed gas of Ar and air (volume ratio 1:1) at a cooling rate of 50°C / min, to obtain a second product;

[0074] (4) The second product was washed, soaked, and dried in deionized water, and was finally crushed and sieved to obtain a positive electrode material.

[0075] Examples 2-10

[0076] The difference from Example 1 is that the holding time in step (3) was adjusted to 13 hours, 12 hours, 11 hours, 10 hours, 8 hours, 6 hours, 5.5 hours, 5 hours, 4 hours, and 3 hours, respectively, to control the content of Na element in the positive electrode material.

[0077] Manufacture of a button cell

[0078] The positive electrode material, the binder polyvinylidene fluoride (PVDF), and the conductive agent conductive carbon black (Super P) in a weight ratio of 90:5:5 were mixed, added into N-methyl pyrrolidone (NMP), and uniformly mixed to prepare a positive electrode slurry with a solid content of 0.7; the mixed positive electrode slurry was uniformly coated on an aluminum foil with a coating thickness of 40 μm, and single-sided coating was performed; after drying, rolling was performed to prepare the required electrode, wherein the electrode coating area density was 14 mg / cm 2 , and punching was performed to obtain a single-sided positive electrode sheet with a diameter of 14 mm; a separator film was punched into a circular sheet with a diameter of 18 mm; a lithium metal sheet with a diameter of 18 mm was used as the negative electrode; LiPF6 was added into a solvent prepared by mixing propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (PC:EC:DEC in a weight ratio of 1:1:1) to obtain an electrolyte; the mass concentration of LiPF6 was 12.5% based on the total weight of the electrolyte; the positive electrode sheet, the separator film, the negative electrode sheet (lithium sheet), the electrolyte, and other accessories were moved into a glove box (the water content needed to be less than 11 ppm); the battery was assembled in the order of bottom to top and injected with the electrolyte: the negative electrode shell > the flat pad + an appropriate amount of electrolyte > the metal lithium sheet + an appropriate amount of electrolyte > one layer of the separator film + an appropriate amount of electrolyte > the positive electrode sheet + an appropriate amount of electrolyte > the flat pad + an appropriate amount of electrolyte > the spring sheet > the positive electrode shell; the battery was packaged on a packaging machine to obtain a button cell.

[0079] Manufacture of a lithium-ion soft-pack battery

[0080] Preparation of the positive electrode: the positive electrode material, the binder polyvinylidene fluoride (PVDF), and the conductive agent conductive carbon black (Super P) in a weight ratio of 96:2:2 were mixed, added into N-methyl pyrrolidone (NMP), and uniformly mixed to prepare a positive electrode slurry with a solid content of 0.7; the mixed positive electrode slurry was uniformly coated on one side surface of an aluminum foil, and the above steps were repeated on the other side surface of the aluminum foil after drying to obtain a double-sided coated positive electrode sheet; cold pressing, cutting, and welding of the tabs were performed to obtain the positive electrode.

[0081] Preparation of the negative electrode: artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose (CMC) were 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 was uniformly coated on one side surface of a copper foil, and the above steps were repeated on the other side surface of the copper foil after drying to obtain a double-sided coated negative electrode sheet; cold pressing, cutting, and welding of the tabs were performed to obtain the negative electrode.

[0082] Preparation of electrolyte: under dry argon atmosphere, LiPF6 was added into a solvent mixed from propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (weight ratio of PC:EC:DEC 1:1:1) to obtain an electrolyte, wherein the mass concentration of LiPF6 was 12.5% based on the total weight of the electrolyte.

[0083] Preparation of separator film: a porous polyethylene (PE) polymer film was used as the separator film.

[0084] Assembly of lithium ion soft package battery: the positive electrode, the separator film, and the negative electrode were stacked in order, with the separator film between the positive electrode and the negative electrode to play a separating role, and then wound to obtain a bare battery cell. The bare battery cell was placed in an outer packaging aluminum plastic film, electrolyte was injected, and then packaged, and after processes such as formation, degassing, and edge cutting, a lithium ion soft package battery was obtained.

[0085] Examples 11-24

[0086] The difference from Example 7 is that step (2) is performed as follows:

[0087] (2) The nickel-manganese precursor, sodium carbonate, and element M source (potassium carbonate, magnesium carbonate, scandium oxide, barium carbonate) were mixed uniformly according to the molar ratio of (Ni+Mn):Na 1:1.05 and M:(Ni+Mn+M) according to the ratio shown in Table 1, calcined at 800°C in air for 20h, and then crushed, sieved, and demagnetized to obtain a first product.

[0088] Comparative Example 1

[0089] Preparation of positive electrode material: (1) a mixed solution containing NiSO4 and MnSO4 was prepared according to the molar ratio of elements Ni:Mn=50:50, and then mixed with a precipitating agent (NaOH solution) and a complexing agent (ammonia water) to react, with the reaction time controlled at 60 hours, the ammonia water concentration controlled at 1 mol / L, and the pH controlled at 12.2, to obtain a nickel-manganese precursor T(OH)2 with an average particle size Dv50 of 11 μm; (2) the nickel-manganese precursor and lithium carbonate in the above step were mixed uniformly according to the molar ratio of Li:(Ni+Mn) 1.02, calcined at 800°C in air for 20h, cooled to room temperature at a rate of 10°C / min, and finally crushed and sieved to obtain a positive electrode material.

[0090] Comparative Example 2

[0091] Preparation of the positive electrode material: (1) A mixed solution containing NiSO4, CoSO4, and MnSO4 was prepared according to the element molar ratio of Ni:Co:Mn = 80:10:10, and was mixed with a precipitant (NaOH solution) and a complexing agent (ammonia water) for reaction. The ternary precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2was obtained by controlling the reaction time to be 48 hours, the ammonia water concentration to be 1 mol / L, and the pH to be 12.8; (2) The ternary precursor in the above step and lithium hydroxide were mixed uniformly according to the molar ratio of Li:(Ni+Co+Mn) = 1.02, and were calcined at 750°C in an oxygen atmosphere for 20h, and then were cooled to room temperature at a rate of 10°C / min. Finally, the positive electrode material was obtained after crushing and sieving.

[0092] Test method

[0093] 1. Cell volume change rate test at the time of charging to a specified voltage

[0094] For the initial positive electrode material synthesized in the examples and comparative examples, X-ray powder diffraction (XRD, instrument model: Bruker D8 ADVANCE, target material: Cu Kα; voltage and current: 40KV / 40mA, scanning angle range: 10° to 70°) was used for testing; and the XRD results were fitted according to the Retiveld fitting method, and the cell parameters a, c and the cell volume V were obtained from the fitting results.

[0095] The coin cell was charged at a current of 0.1C to a specified voltage (for example, 4.0V or 4.4V) in the range of 2.8V to 4.4V, and the positive electrode sheet was obtained by disassembly, soaked and cleaned with dimethyl carbonate (DMC), and dried for the above XRD test. The XRD results were fitted according to the Retiveld fitting method, and the cell volume V’ was obtained from the fitting results. The corresponding charge gram capacity and cell volume V’ were recorded, and the relationship between the cell volume and the charge gram capacity was obtained.

[0096] The cell volume change rate AV = (V’-V) / V x 100%.

[0097] 2. 4.45V floating charge thickness expansion rate test

[0098] The lithium ion soft package battery is charged at 45℃ with 1C constant current to 4.45V, then charged at 4.45V constant voltage to the current of 0.05C, the thickness of the battery at this time is tested and recorded with a micrometer, and is recorded as H0; 45℃ is placed for 1h, and is charged at 0.4C constant current to 4.45V, then charged at 4.45V constant voltage for 1000h, the thickness of the battery at this time is tested and recorded with a micrometer, and is recorded as H1; the thickness expansion rate of 4.45V floating charge = (H1-H0) / H0x100%.

[0099] 3. High temperature storage capacity recovery rate test

[0100] The lithium ion soft package battery is charged at 25℃ with 0.7C constant current to 4.35V, then charged at 4.35V constant voltage to the current of 0.02C, so that the lithium ion soft package battery reaches the full charge state, then discharged at 0.2C constant current to 3.0V, and the above steps are repeated twice, and the discharge capacity of the second cycle is counted as C1; then the lithium ion soft package battery is fully charged according to the above steps, and is placed in a 60℃ constant temperature oven for 60 days. After taking out the battery, the battery is placed in a constant temperature oven at 25℃, and the above charging and discharging steps are repeated twice, and the discharge capacity of the second cycle is counted as C2; the high temperature storage capacity recovery rate = C2 / C1x100%.

[0101] 4. 6C discharge temperature rise test

[0102] The lithium ion soft package battery is charged at 25℃ with 1C constant current to 4.35V, then charged at 4.35V constant voltage to the current of 0.05C. Then discharged at 6C rate constant current to 2.8V, in the process the battery is tightly wrapped with thermal insulation cotton, and the change of battery temperature is tested with a thermocouple, and the 6C discharge temperature rise (℃) = temperature after discharge-25℃.

[0103] 5. DCR test

[0104] The lithium ion soft package battery is charged at room temperature with 1C constant current to 4.35V, then charged at 4.35V constant voltage to the current of 0.05C, so that the lithium ion soft package battery reaches the full charge state. Then discharged at 0.2C rate to 50% SOC, at this time the voltage is recorded as V0, then discharged at 0.1C current for 10s, at this time the voltage is recorded as V1, the current and voltage change are recorded, and DCR = (V0-V1) / I.

[0105] 6. TG-MS / DSC linkage test

[0106] After the button cell is fully charged to 4.4V at a charge rate of 0.1C, it is disassembled, and the disassembled positive electrode sheet is soaked in dimethyl carbonate (DMC) to remove the residual electrolyte. After natural air drying, it is transferred to a TG-MS / DSC linkage device, and is heated to 700℃ at a heating rate of 3℃ / min. Oxygen signals generated during the collection process are collected.

[0107] Test results

[0108] The test results of the button cells and lithium ion soft package cells obtained by the examples and comparative examples are shown in Table 1. From the comparison of Examples 1-24 and Comparative Example 1, it can be seen that the positive electrode material of the examples of the present application has Na element doping in the lithium layer and is rich in oxygen vacancies inside and on the surface of the material, so that the cell volume change rate AV1 of the material at 4.4V is greatly increased, and in turn the positive electrode material has higher charge gram capacity at 4.4V charging state, thereby greatly improving the energy density of the lithium ion battery. At the same time, from the comparison of Examples 1-24 and Comparative Example 2, it can be seen that the positive electrode material in the examples of the present application has higher oxygen release initiation temperature on the basis of higher charge gram capacity, indicating that the oxygen vacancies formed inside and on the surface of the positive electrode material of the present application reduce the activity of oxygen in the material, and the Na element doping in the lithium layer inhibits the structural collapse of the material in the high delithiation state, thereby inhibiting the oxygen release of the positive electrode material and improving the structural stability of the positive electrode material at high temperature and high voltage, so that the lithium ion battery has lower floating thickness expansion rate and higher high-temperature storage capacity recovery rate. In addition, the positive electrode material in the examples of the present application has a larger cell parameter c, and the corresponding lithium ion battery has a significantly reduced 6C discharge temperature rise and DCR, indicating that the positive electrode material of the examples of the present application can increase the lithium-oxygen layer spacing due to the Na element doping in the lithium layer and the rich oxygen vacancies inside and on the surface of the material, promote the full deintercalation of lithium ions, and thereby improve the kinetic performance of the material.

[0109]

[0110]

[0111] Examples 25-39

[0112] The difference from Example 1 is that the electrolyte is prepared as follows: under a dry argon environment, additives are added to a solvent composed of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (weight ratio of PC:EC:DEC 1:1:1) according to Table 2, and then LiPF6 is added and mixed uniformly to obtain the electrolyte, wherein the content of the additives and LiPF6 is based on the total weight of the electrolyte, and the mass concentration of LiPF6 is 12.5%.

[0113] Table 2

[0114]

[0115] As can be seen from the comparison of Examples 25-39 in Table 2 with Example 1, by further adding a compound containing a sulfur-oxygen double bond and / or a polynitrile compound in the electrolyte, the high-temperature storage capacity recovery rate of the lithium ion battery can be further improved. The possible reason is that the compound containing a sulfur-oxygen double bond can form a protective film resistant to oxidation 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 from the surface of the positive electrode material and the oxidative decomposition of the electrolyte. The polynitrile 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 from the surface of the positive electrode material, thereby improving the structural stability of the positive electrode material under high-temperature storage.

[0116] While some example embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. Rather, it should be recognized that there are numerous modifications and changes that can be made to the embodiments described and that such modifications and changes are contemplated as being within the scope of the present application.

Claims

1. A positive electrode material, characterized by, The electrode comprising the positive electrode material is assembled into a button cell with lithium sheet, and when the button cell is charged at a current of 0.1C to 4.4V in a voltage range of 2.8V to 4.4V, the charge specific capacity of the positive electrode material is greater than or equal to 220mAh / g based on the weight of the positive electrode material, and the cell volume change rate ΔV1 of the positive electrode material is 7% to 11%.

2. The positive electrode material of claim 1, wherein, The electrode comprising the positive electrode material is assembled into a button cell with lithium sheet, and when the button cell is charged at a current of 0.1C to 4.0V in a voltage range of 2.8V to 4.4V, the cell volume change rate ΔV2 of the positive electrode material is less than or equal to 3.5%.

3. The positive electrode material of claim 1, wherein, The cell parameters a, cell parameters c and cell volume V of the positive electrode material satisfy at least one of the following conditions: (1) (2) (3) 4. The cathode material of claim 1, wherein, When the button cell is charged at a current of 0.1C to 4.4V in a voltage range of 2.8V to 4.4V, the oxygen release onset temperature of the positive electrode material is greater than or equal to 220℃.

5. The cathode material of claim 1, wherein, The electrode comprising the positive electrode material is assembled into a button cell with lithium sheet, and when the button cell is charged and discharged at a current of 0.1C in a voltage range of 2.8V to 4.4V, the obtained capacity voltage differential dQ / dV curve has a first oxidation peak and a first reduction peak in the range of 4.2V to 4.4V.

6. The cathode material of claim 1, 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 M, the element T comprises at least one of Ni, Co or Mn, and the element M 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 mole percentage content of Ni is 30% to 70% based on the total mole amount of the element T; (2) the mole percentage content of Mn is 0% to 70% based on the total mole amount of the element T; (3) the mole percentage content of Co is 0% to 50% based on the total mole amount of the element T; (4) the mole percentage content of the element T is 90% to 100% and the mole percentage content of the element M is 0% to 10% based on the total mole amount of the element T and the element M; (5) the lithium transition metal composite oxide further comprises an element R, the element R comprises at least one of F, Cl, Br, I or N, and the mole percentage content of the element R is 0.1% to 10% based on the total mole amount of the element T and the element M; (6) the ratio of the mole amount of Li element to the total mole amount of the element T and the element M in the lithium transition metal composite oxide is 0.5 to 1.

1.

7. The positive electrode material according to claim 6, characterized in that, The lithium transition metal composite oxide satisfies at least one of the following conditions: (1) the lithium transition metal composite oxide further comprises a Na element, and the mole percentage content of the Na element is 0.1% to 20% based on the total mole amount of the element T and the element M; (2) the lithium transition metal composite oxide has a layered crystal structure; (3) the lithium transition metal complex oxide includes Li x1 Na x2 Ni y1 Mn y2 Co y3 M z1 O 2±m R m , 0.5≤x1≤1.1, 0.001≤x2≤0.2, 0.3≤y1≤0.7, 0≤y2≤0.7, 0≤y3≤0.5, 0≤z1≤0.1, 0≤m≤0.1, wherein the element R includes at least one of F, Cl, Br, I, or N.

8. An electrochemical device, characterized by, The electrochemical device comprises a positive electrode sheet, and the positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 7.

9. The electrochemical device of claim 8, wherein, The electrochemical device further comprises an electrolyte, wherein the electrolyte comprises an additive, the additive comprises at least one of a sulfur-oxygen double bond-containing compound or a polynitrile compound, and the electrolyte satisfies at least one of the following conditions: (1) the sulfur-oxygen double bond-containing compound comprises at least one of 1,3-propane sultone, vinyl sulfate, 2,4-butane sultone, 1,4-butane sultone, methane dimesylate, 1,3-propane disulfonic anhydride, 4-methyl ethylene sulfate or pentaerythritol bis cyclic sulfate; (2) the mass percentage 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, nonanedinitrile, melononitrile, methyl glutaronitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3,5-pentanetricarbonitrile, 1,3,6-hexanetricarbonitrile or 1,2,3-tris(2-cyanoethoxy)propane; (4) the mass percentage of the polynitrile compound is 0.5% to 10% based on the mass of the electrolyte.

10. An electronic device comprising the electrochemical device according to claim 8 or 9.

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