Positive electrode material, electrochemical device, and electronic device

Abstract

A cathode material, an electrochemical device, and an electronic device are disclosed. An electrode comprising the cathode material is assembled with a lithium sheet to form a coin cell. When the coin cell is charged to 4.4V, the lithium removal rate of the cathode material is above 80%. The cathode material exhibits high lithium removal rate and good structural stability at high voltage, thereby enabling the electrochemical device to have high energy density, good float charging performance, and high-temperature storage performance.

Description

Technical Field

[0001] This application relates to the field of energy storage, specifically to a cathode material, an electrochemical device, and an electronic device. Background Technology

[0002] With the widespread adoption of consumer electronics such as laptops, mobile phones, tablets, power banks, and drones, the requirements for their batteries are becoming increasingly stringent. For example, batteries are not only required to be lightweight, but also to have high capacity and long lifespan. Lithium-ion batteries, with their outstanding advantages such as high energy density, high safety, no memory effect, and long lifespan, have already gained a mainstream position in the market.

[0003] In pursuit of higher energy density, lithium-ion batteries have been continuously developed towards increasing voltage and lithium removal capacity. However, at high voltages and with high lithium removal capacity, the problems of oxygen release and structural phase transitions on the cathode material surface are fully exposed, leading to issues such as battery cycle degradation and gas generation. Therefore, there is an urgent need to develop a cathode material with high lithium removal capacity and high stability at high voltages. Summary of the Invention

[0004] In view of this, in a first aspect, this application provides a positive electrode material, wherein an electrode including the positive electrode material is assembled with a lithium sheet to form a coin cell, wherein when the coin cell is charged to 4.4V, the amount of lithium delithiation of the positive electrode material is more than 80%.

[0005] Typically, the capacity of ternary cathode materials is primarily generated by the valence changes of nickel and cobalt. The capacity of the cathode material is related to its nickel content; the higher the nickel content, the higher the capacity. However, manganese (Mn) in the cathode material is in the +4 valence state, which does not contribute to capacity and further limits the energy density of the material. Simultaneously, the low electrochemical activity of manganese leads to poor material kinetics. Under deep delithiation, the high activity of oxygen ions on the material surface easily leads to side reactions with the electrolyte, resulting in increased interfacial impedance or gas generation. Furthermore, a low lithium-oxygen interlayer spacing in ternary materials will hinder lithium-ion diffusion at the end of charging, resulting in a lower battery capacity.

[0006] The inventors of this application have discovered that elemental doping in the lithium layer through synthesis can control the internal oxygen defects and the lithium-oxygen interlayer spacing of the material. Introducing oxygen defects into the material can activate the redox properties of the transition metal, significantly improving the energy density of the material. Simultaneously, doping the lithium layer with elements of high ionic radius increases the lithium-oxygen interlayer spacing, promoting the full insertion and extraction of lithium ions, thereby significantly increasing the amount of lithium removed from the cathode material. Furthermore, the oxygen vacancies formed on the surface can reduce the activity of oxygen on the material surface, stabilize oxygen ions in the outer layer, and suppress oxygen release and gas generation during float charging and high-temperature storage of the cathode material, thereby improving the float charging performance and high-temperature storage performance of the electrochemical device.

[0007] According to some embodiments of this application, when the coin cell is charged to 4.4V, the strongest oxygen release peak of the cathode material in the TG-MS test within the range of 100℃ to 500℃ is above 250℃. The oxygen vacancies formed inside and on the surface of the cathode material of this application reduce the oxygen activity in the material, and the elemental doping in the lithium layer inhibits the structural collapse of the material under high delithiation conditions, thereby suppressing oxygen release from the cathode material and improving the structural stability of the cathode material under high temperature and high voltage.

[0008] According to some embodiments of this application, when the coin cell is charged to 4.4V, based on a mass of 50mg of the positive electrode material, the oxygen ion current intensity of the positive electrode material in TG-MS testing is IA / 50mg, and the temperature is T℃, wherein, in the range of 100℃ to 500℃, the differential of I with respect to T, dI / dT, is less than or equal to 3×10⁻⁶. -13 The cathode material of this application can suppress the violent release of oxygen from the material, thereby improving the structural stability of the cathode material under high temperature and high voltage.

[0009] According to some embodiments of this application, when the coin cell is charged to 4.4V, based on a mass of 50mg of the positive electrode material, the heat release of the positive electrode material in a TG-DSC test is W mW / 50mg at a temperature of T℃, wherein, within the range of 100℃ to 500℃, the differential of W with respect to T, dW / dT, is less than or equal to 0.01. The positive electrode material of this application can suppress the violent oxygen release and heat release of the material, thus improving the structural stability of the positive electrode material under high temperature and high voltage.

[0010] According to some embodiments of this application, an electrode including the positive electrode material is assembled with a lithium sheet to form a coin cell. When the coin cell is charged and discharged at a current of 0.1C in the voltage range of 3.0V 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.

[0011] According to some embodiments of this application, the peak voltage of the first oxidation peak is Vo1, the peak voltage of the first reduction peak is Vr1, and |Vol-Vr1|≤0.3V.

[0012] According to some embodiments of this application, the capacity-voltage differential dQ / dV curve has a second oxidation peak and a second reduction peak in the range of 3.6V to 4.0V. The peak voltage of the second oxidation peak is Vo2, the peak voltage of the second reduction peak is Vr2, and |Vo2-Vr2|≤0.3V.

[0013] According to some embodiments of this application, the cathode material comprises a lithium transition metal composite oxide, which comprises element T and optionally element Q. Element T comprises at least one of Ni, Co, or Mn, and 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.

[0014] In some embodiments, the molar percentage of Ni is 30% to 70% based on the total molar amount of element T. In some embodiments, the molar percentage of Mn is 0% to 70% based on the total molar amount of element T. In some embodiments, the molar percentage of Co is 0% to 50% based on the total molar amount of element T.

[0015] According to some embodiments of this application, the lithium transition metal composite oxide further includes Na element, and the molar percentage content of Na element is 0.1% to 20% based on the total molar amount of the elements T and Q.

[0016] According to some embodiments of this application, based on the total molar amount of elements T and Q, the molar percentage of element T is 90% to 100%, and the molar percentage of element Q is 0% to 10%.

[0017] According to some embodiments of this application, the lithium transition metal composite oxide further includes element R, which includes at least one of F, Cl, Br, I or N, and the molar percentage of element R is 0.1% to 10% based on the total molar amount of elements T and Q.

[0018] According to some embodiments of this application, in the lithium transition metal composite oxide, the ratio of the molar amount of Li to the total molar amount of elements T and Q is 0.5 to 1.1.

[0019] According to some embodiments of this application, the lithium transition metal composite oxide has a layered crystal structure.

[0020] According to some embodiments of this application, the lithium transition metal composite oxide includes Li x1 Na x2 Ni y1 Mn y2 Co y3 Q 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 element R includes at least one of F, Cl, Br, I or N.

[0021] In a second aspect, this application also provides an electrochemical device comprising a positive electrode plate comprising the positive electrode material according to the first aspect of this application.

[0022] In some embodiments, the electrochemical device further includes an electrolyte, wherein the electrolyte contains additives, the additives including at least one of sulfur-containing oxygen double bond compounds or polynitrile compounds. Sulfur-containing oxygen double bond compounds can form an oxidation-resistant protective film on the surface of the cathode material, and the abundant sulfur can stabilize high-valence transition metals in the charged state, thereby better suppressing oxygen release from the cathode material surface and the oxidative decomposition of the electrolyte. Polynitrile compounds can complex with transition metals on the surface of the cathode active material, stabilizing transition metals such as nickel, cobalt, and manganese on the cathode material surface, suppressing oxygen release from the cathode material surface, thereby improving the structural stability of the cathode material under high temperature and high voltage.

[0023] According to some embodiments of this application, the sulfur-containing oxygen double bond compound includes at least one of 1,3-propanesulfonyl lactone, vinyl sulfate, 2,4-butanesulfonyl lactone, 1,4-butanesulfonyl lactone, methylene disulfonate, 1,3-propane disulfonic anhydride, 4-methyl ethylene sulfate, or pentaerythritol bicyclic sulfate.

[0024] According to some embodiments of this application, the mass percentage of the sulfur-containing oxygen double bond compound is 0.1% to 5% based on the mass of the electrolyte.

[0025] According to some embodiments of this application, the polynitrile compound includes at least one selected from butadionitrile, glutaronitrile, adiponitrile, heptadionitrile, octadionitrile, nonadionitrile, succinate, methylglutaronitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3,5-pentanetricarbonyl, 1,3,6-hexanetrionitrile, or 1,2,3-tris(2-cyanoethoxy)propane.

[0026] According to some embodiments of this application, the mass percentage of the polynitrile compound is 1% to 10% based on the mass of the electrolyte.

[0027] In a third aspect, this application provides an electronic device that includes the electrochemical device described in the second aspect of this application. Attached Figure Description

[0028] Figure 1The oxygen ion flux intensity curves obtained by TG-MS testing for Comparative Example 2 and Example 21 are shown.

[0029] Figure 2 The differential curves of oxygen ion flow intensity versus temperature obtained by TG-MS testing of Comparative Example 2 and Example 1 are shown.

[0030] Figure 3 The initial charge-discharge curves of Comparative Examples 1, 2 and Example 15 are shown.

[0031] Figure 4 The capacity voltage differential dQ / dV curves for Comparative Examples 1, 2 and Example 15 are shown. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of this application. The embodiments of this application should not be construed as limiting this application.

[0033] For the sake of brevity, this article only discloses a few specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0034] In this description, unless otherwise stated, "above" and "below" include the stated number.

[0035] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0036] The list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0037] I. Cathode Materials

[0038] In a first aspect, this application provides a positive electrode material, wherein an electrode comprising the positive electrode material is assembled with a lithium sheet to form a coin cell, wherein when the coin cell is charged to 4.4V, the amount of delithiation of the positive electrode material is above 80%, for example, it can be 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, or 100%.

[0039] In this application, the amount of lithium removed is obtained by testing as follows: For the synthesized initial cathode material, firstly, the molar percentage A of lithium relative to the total molar amounts of elements T (Ni / Co / Mn) and Q is obtained by inductively coupled plasma spectrometry (ICP); then, the synthesized initial cathode material is assembled with lithium sheets into a coin cell, and the coin cell is charged to 4.4V at a constant current of 0.1C within a voltage range of 3.0V to 4.4V. The cathode material is then disassembled, and the molar percentage B of lithium relative to the total molar amounts of elements T (Ni / Co / Mn) and Q in the cathode material at the 4.4V state is obtained by ICP testing. The amount of lithium removed = (1-B / A)×100%. For the cathode material in the full cell, the difference lies only in that the full cell is first fully discharged, and then the battery is disassembled to obtain the cathode material. The molar percentage A of lithium relative to the total molar amounts of elements T (Ni / Co / Mn) and Q in the cathode material is obtained by ICP testing.

[0040] The inventors of this application have discovered that elemental doping in the lithium layer through synthesis can control the internal oxygen defects and the lithium-oxygen interlayer spacing of the material. Introducing oxygen defects into the material can activate the redox properties of the transition metal, significantly improving the energy density of the material. Simultaneously, doping the lithium layer with elements of high ionic radius increases the lithium-oxygen interlayer spacing, promoting the full insertion and extraction of lithium ions, thereby significantly increasing the amount of lithium removed from the cathode material. Furthermore, the oxygen vacancies formed on the surface can reduce the activity of oxygen on the material surface, stabilize oxygen ions in the outer layer, and suppress oxygen release and gas generation during float charging and high-temperature storage of the cathode material, thereby improving the float charging performance and high-temperature storage performance of the electrochemical device.

[0041] In some embodiments, when the coin cell is charged to 4.4V, the strongest oxygen release peak of the cathode material in TG-MS testing within the range of 100℃ to 500℃ is above 250℃, for example, it can be 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, or 400℃. The oxygen vacancies formed inside and on the surface of the cathode material of this application reduce the oxygen activity in the material, and the elemental doping in the lithium layer inhibits the structural collapse of the material in a high delithiation state, thereby suppressing oxygen release from the cathode material and improving the structural stability of the cathode material under high temperature and high voltage.

[0042] In some embodiments, when the coin cell is charged to 4.4V, based on a mass of 50mg of the positive electrode material, the oxygen ion current intensity of the positive electrode material in TG-MS testing is IA / 50mg, and the temperature is T℃, wherein, in the range of 100℃ to 500℃, the differential of I with respect to T, dI / dT, is less than or equal to 3×10⁻⁶. -13 The cathode material of this application can suppress the violent release of oxygen from the material, thereby improving the structural stability of the cathode material under high temperature and high voltage.

[0043] In some embodiments, when the coin cell is charged to 4.4V, based on a mass of 50mg of the cathode material, the heat release of the cathode material in a TG-DSC test is W mW / 50mg, and the temperature is T℃. Wherein, within the range of 100℃ to 500℃, the differential of W with respect to T, dW / dT, is less than or equal to 0.01, for example, it can be 0.01, 0.009, 0.008, 0.007, 0.006, 0.005, 0.004, 0.003, 0.002, 0.001, or any range thereof. The cathode material of this application can suppress the violent oxygen release and heat release of the material, improving the structural stability of the cathode material under high temperature and high voltage.

[0044] In some embodiments, an electrode including the positive electrode material is assembled with a lithium sheet to form a coin cell. When the coin cell is charged and discharged at a current of 0.1C in the voltage range of 3.0V 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.

[0045] In some embodiments, the peak voltage of the first oxidation peak is Vol, the peak voltage of the first reduction peak is Vrl, and |Vol-Vrl|≤0.3V. For example, the value of |Vol-Vrl| can be 0.01V, 0.05V, 0.10V, 0.15V, 0.20V, 0.25V, 0.30V, or any range thereof.

[0046] In some embodiments, the capacitance-voltage differential dQ / dV curve exhibits a second oxidation peak and a second reduction peak in the 3.6V to 4.0V range. The peak voltage of the second oxidation peak is Vo2, and the peak voltage of the second reduction peak is Vr2, with |Vo2-Vr2| ≤ 0.3V. For example, the value of |Vo2-Vr2| can be 0.01V, 0.05V, 0.10V, 0.15V, 0.20V, 0.25V, 0.30V, or any range thereof.

[0047] In some embodiments, the cathode material comprises a lithium transition metal composite oxide, which comprises element T and optionally element Q. Element T comprises at least one of Ni, Co, or Mn, and 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.

[0048] In some embodiments, the molar percentage of Ni, based on the total molar amount of element T, is 30% to 70%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any range thereof. In some embodiments, the molar percentage of Mn, based on the total molar amount of element T, is 0% to 70%, for example, 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any range thereof. In some embodiments, the molar percentage of Co, based on the total molar amount of element T, is 0% to 50%, for example, 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any range thereof.

[0049] In some embodiments, the lithium transition metal composite oxide further includes Na element, and the molar percentage content of Na element is 0.1% to 20% based on the total molar amount of the elements T and Q, for example, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 20% or any range thereof.

[0050] In some embodiments, based on the total molar amount of elements T and Q, the molar percentage of element T is 90% to 100%, for example, 90%, 91%, 94%, 96%, 98%, 99%, 100% or any range thereof, and the molar percentage of element Q is 0% to 10%, for example, 0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 8%, 10% or any range thereof.

[0051] In some embodiments, the lithium transition metal composite oxide further includes element R, which includes at least one of F, Cl, Br, I or N, and the molar percentage of element R is 0.1% to 10% based on the total molar amount of elements T and Q, for example, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any range thereof.

[0052] In some embodiments, the ratio of the molar amount of Li to the total molar amount of T and 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 any range thereof.

[0053] In some embodiments, the lithium transition metal composite oxide has a layered crystal structure.

[0054] In some embodiments, the lithium transition metal composite oxide includes Li x1 Na x2 Ni y1 Mn y2 Co y3 Q 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 element R includes at least one of F, Cl, Br, I or N.

[0055] II. Electrochemical Device

[0056] The electrochemical device provided in this application includes a positive electrode, which includes the positive electrode material described in the first aspect of this application.

[0057] In some embodiments, the positive electrode further includes a conductive agent and a binder. In some embodiments, the binder includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride, or polyvinylidene fluoride-hexafluoropropylene copolymer, etc. In some embodiments, the conductive agent includes, 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 nanotubes, 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.

[0058] In some embodiments, the positive electrode further includes a positive current collector. In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material on a polymer substrate.

[0059] In some embodiments, the electrochemical device further includes a negative electrode.

[0060] In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector. In some embodiments, the negative electrode active material layer includes a negative electrode active material. In some embodiments, the negative electrode active material includes at least one of a carbon material or a silicon material. The carbon material includes at least one of graphite and hard carbon, and the silicon material includes at least one of silicon, silicon oxide, silicon carbide, or silicon alloy. In some embodiments, the negative electrode active material layer includes an adhesive. In some embodiments, the adhesive includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, or styrene-butadiene rubber. In some embodiments, the negative electrode active material layer further includes a conductive material to improve electrode conductivity. In some embodiments, the conductive material includes at least one of conductive carbon black, acetylene black, carbon nanotubes, Ketjen black, or graphene.

[0061] In some embodiments, the electrochemical device further includes an electrolyte or a solid electrolyte.

[0062] In some embodiments, the electrolyte used in this application may be an electrolyte known in the prior art.

[0063] 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(fluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive comprises at least one of a sulfur-containing oxygen double bond compound or a polynitrile compound.

[0064] In some embodiments, the sulfur-containing oxygen double bond compound comprises at least one selected from 1,3-propanesulfonyl lactone, vinyl sulfate, 2,4-butanesulfonyl lactone, 1,4-butanesulfonyl lactone, methylene disulfonate, 1,3-propane disulfonic anhydride, 4-methylethylene sulfate, or pentaerythritol bicyclic sulfate. In some embodiments, based on the mass of the electrolyte, the mass percentage of the sulfur-containing oxygen double bond compound is from 0.1% to 5%, for example, 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 thereof. In some embodiments, the polynitrile compound includes at least one selected from succinic anionizer, glutaronitrile, adiponitrile, heptanilide, octanoic anionizer, nonadionitrile, succinic anionizer, methylglutaronitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3,5-pentanetricarbonyl, 1,3,6-hexanetrionitrile, or 1,2,3-tris(2-cyanoethoxy)propane. In some embodiments, based on the mass of the electrolyte, the mass percentage of the polynitrile compound is from 1% to 10%, for example, 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 thereof.

[0065] In some embodiments, a separator is provided between the positive and negative electrodes in the electrochemical device to prevent short circuits. The material and shape of the separator used in the embodiments of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application. For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with 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 membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected. At least one surface of the substrate layer is provided with a surface treatment layer, which can be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. The inorganic layer comprises inorganic particles and a binder. The inorganic particles include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene, or polyhexafluoropropylene. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or a copolymer of polyvinylidene fluoride and hexafluoropropylene.

[0066] In some embodiments, the electrochemical device of this application includes, but is not limited to, all types of primary or secondary batteries. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to, lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0067] III. Electronic Devices

[0068] The electronic device described in this application can be any device that uses the electrochemical device described in the second aspect of this application.

[0069] In some embodiments, the electronic device includes, but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries or lithium-ion capacitors, etc.

[0070] Examples and Comparative Examples

[0071] Example 1

[0072] Preparation of cathode materials

[0073] (1) A mixed solution containing NiSO4 and MnSO4 was prepared according to the elemental molar ratio Ni:Mn = 50:50. The mixed solution was then mixed with a precipitant (NaOH solution) and a complexing agent (ammonia water) and reacted. The reaction time was controlled at 60 hours, the ammonia water concentration was 1 mol / L, and the pH was 12.2 to obtain a nickel-manganese precursor T(OH)2 (T represents Ni / Mn) with an average particle size Dv50 of 11 μm.

[0074] (2) The above nickel-manganese precursor and sodium carbonate are ground and mixed evenly in a molar ratio of (Ni+Mn):Na of 1:1.05, calcined at 800℃ in air atmosphere for 20h, and then crushed, sieved and demagnetized to obtain the first product.

[0075] (3) The first product above is mixed with a lithium source (a mixture of lithium hydroxide and lithium nitrate in a molar ratio of 1:1) with a mass ratio of lithium source to first product of 10:1. The mixture is heated to 400°C at a rate of 10°C / min and held for 14 hours. Then it is quenched to room temperature in a mixture of Ar and air (volume ratio of 1:1) at a cooling rate of 50°C / min to obtain the second product.

[0076] (4) The second product is washed, soaked and dried in deionized water, and finally crushed and screened to obtain the positive electrode material.

[0077] Example 2-10

[0078] The difference from Example 1 is that the holding time in step (3) is 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 Na content in the cathode material.

[0079] The manufacture of button batteries

[0080] A mixture of positive electrode material, binder polyvinylidene fluoride (PVDF), and conductive agent conductive carbon black (Super P) in a weight ratio of 90:5:5 was added and mixed thoroughly with N-methylpyrrolidone (NMP) to form a positive electrode slurry with a solid content of 0.7%. The mixed positive electrode slurry was then uniformly coated onto aluminum foil to a thickness of 40 μm on one side. After drying, the coating was rolled to form the desired electrode, wherein the electrode coating surface density was 14 mg / cm³. 2 The positive electrode is obtained by drying and then punched into 14mm round sheets to obtain a single-sided positive electrode; the separator is punched into 18mm round sheets; the negative electrode used is a lithium metal sheet with a diameter of 18mm; LiPF6 is added to a solvent composed of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (PC:EC:DEC weight ratio 1:1:1) and mixed evenly to obtain an electrolyte; based on the total weight of the electrolyte, the LiPF6... The mass concentration is 12.5%. The positive electrode, separator, negative electrode (lithium sheet), electrolyte, battery casing, and other accessories are moved into a glove box (water content must be less than 11 ppm). The battery is assembled and injected with electrolyte in the following stacking order from bottom to top: negative electrode casing > flat pad + appropriate amount of electrolyte > lithium metal sheet + appropriate amount of electrolyte > one layer of separator + appropriate amount of electrolyte > positive electrode + appropriate amount of electrolyte > flat pad + appropriate amount of electrolyte > spring sheet > positive electrode casing. The battery is then packaged on a packaging machine to obtain a button cell.

[0081] Manufacturing of lithium-ion pouch batteries

[0082] 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 are mixed and then mixed evenly with N-methylpyrrolidone (NMP) to prepare a positive electrode slurry with a solid content of 0.7. The mixed positive electrode slurry is evenly coated on one side of an aluminum foil. 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 electrode tabs, the positive electrode is obtained.

[0083] Preparation of the negative electrode: Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose (CMC) are mixed with deionized water at a mass ratio of 96:2:2 and stirred evenly to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on one side of a copper foil, and after drying, the above steps are repeated on the other side of the copper foil to obtain a double-sided coated negative electrode sheet. After cold pressing, cutting, and welding of tabs, the negative electrode is obtained.

[0084] Preparation of electrolyte: Under a dry argon atmosphere, LiPF6 was added to a solvent composed of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (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.

[0085] Preparation of the separator: Polyethylene (PE) porous polymer film was used as the separator.

[0086] Assembly of lithium-ion pouch batteries: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes for isolation. This is then wound to obtain the bare cell. The bare cell is placed in an outer aluminum-plastic film package, electrolyte is injected, and the package is sealed. After processes such as formation, degassing, and edge trimming, the lithium-ion pouch battery is obtained.

[0087] Examples 11-25

[0088] The difference from Example 7 is that step (2) is performed as follows:

[0089] (2) The above nickel-manganese precursor, sodium carbonate and element Q source (calcium hydroxide, strontium hydroxide, chromium trioxide, tungsten trioxide, molybdenum trioxide, niobium pentoxide and zirconium dioxide) are ground and mixed evenly according to the molar ratio of (Ni+Mn)∶Na of 1∶1.05 and the ratio of Q∶(Ni+Mn+Q) as shown in Table 1. The mixture is calcined at 800℃ in air for 20h, and then crushed, sieved and demagnetized to obtain the first product.

[0090] Comparative Example 1

[0091] Preparation of positive electrode material: (1) A mixed solution containing NiSO4 and MnSO4 was prepared according to the elemental molar ratio Ni:Mn = 50:50. The solution was mixed with a precipitant (NaOH solution) and a complexing agent (ammonia water) and reacted. The reaction time was controlled at 60 hours, the ammonia water concentration was 1 mol / L, and the pH was 12.2 to obtain a nickel-manganese precursor Ni with an average particle size Dv50 of 11 μm. 0.5 Mn 0.5 (OH)2; (2) Grind and mix the nickel-manganese precursor and lithium carbonate in the above steps according to the molar ratio of Li: element T (Ni / Mn) of 1.02, calcine at 800℃ in air atmosphere for 20h, cool down to room temperature at a rate of 10℃ / min, and finally obtain the positive electrode material by crushing and sieving.

[0092] Comparative Example 2

[0093] Preparation of cathode material: (1) Prepare a mixed solution containing NiSO4, CoSO4 and MnSO4 according to the elemental molar ratio Ni:Co:Mn = 80:10:10. Mix it with precipitant (NaOH solution) and complexing agent (ammonia water) and react them. Control the reaction time to 48 hours, the ammonia water concentration to 1 mol / L, and the pH to 12.8 to obtain the ternary precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2; (2) The ternary precursor and lithium hydroxide in the above steps are ground and mixed evenly according to the molar ratio of Li: element T (Ni / Co / Mn) of 1.02, calcined at 750℃ in an oxygen atmosphere for 20h, cooled to room temperature at a rate of 10℃ / min, and finally crushed and sieved to obtain the positive electrode material.

[0094] Test methods

[0095] 1. Lithium removal rate test

[0096] For the initial cathode materials synthesized in the examples and comparative examples, the molar percentage A of lithium relative to the total molar amounts of elements T (Ni / Co / Mn) and Q in the initial cathode materials was obtained by inductively coupled plasma spectrometry (ICP).

[0097] The electrode sheet containing the positive electrode material was assembled into a coin cell according to the method described in the embodiment. The coin cell was charged to 4.4V at a constant current of 0.1C. The positive electrode sheet was then disassembled to obtain the positive electrode sheet. The positive electrode material was scraped off, and the molar percentage B of lithium element in the positive electrode material at 4.4V charging was obtained by ICP test. The delithiation amount = (1-B / A)×100%.

[0098] 2. High-Temperature Storage Capacity Recovery Rate Test

[0099] The lithium-ion pouch battery was charged at 25°C with a constant current of 0.7C to 4.35V, then charged at 4.35V with a constant voltage until the current reached 0.02C, bringing the lithium-ion pouch battery to a fully charged state. Next, it was discharged at a constant current of 0.2C to 3.0V. This process was repeated twice, and the discharge capacity of the second cycle was recorded as C1. The lithium-ion pouch battery was then fully charged again using the same steps and stored in a 60°C constant temperature chamber for 60 days. After storage, the battery was removed and placed at 25°C for two more charge-discharge cycles, and the discharge capacity of the second cycle was recorded as C2. The high-temperature storage capacity recovery rate = C2 / C1 × 100%.

[0100] 3. 4.45V float charge thickness expansion rate test

[0101] The lithium-ion pouch battery was charged at 45℃ with a constant current of 1C to 4.45V, and then charged at 4.45V with a constant voltage until the current was 0.05C. The thickness of the battery at this point was measured and recorded with a micrometer and denoted as H0. After standing at 45℃ for 1 hour, it was charged at a constant current of 0.4C to 4.45V, and then charged at 4.45V with a constant voltage for 1000 hours. The thickness of the battery at this point was measured and recorded with a micrometer and denoted as H1. The thickness expansion rate at 4.45V float charging = (H1-H0) / H0×100%.

[0102] 4. TG-MS / DSC linkage test

[0103] The button cell was fully charged to 4.4V at a charging rate of 0.1C and then disassembled. The disassembled positive electrode was soaked in dimethyl carbonate (DMC) to remove residual electrolyte. After air drying, it was transferred to a TG-MS / DSC linkage device and heated to 700℃ at a heating rate of 3℃ / min. The heat and oxygen signals generated during the process were collected.

[0104] The test results of the coin cells and lithium-ion pouch cells obtained in each embodiment and comparative example are shown in Table 1. A comparison of Examples 1-25 with Comparative Example 1 shows that the cathode material of this application, due to the Na doping of the lithium layer and the abundance of oxygen vacancies inside and on the surface of the material, exhibits a first oxidation peak and a first reduction peak in the dQ / dV curve of the assembled coin cell in the 4.2V to 4.4V range. This results in a higher amount of lithium removal from the cathode material at a charging state of 4.4V, thereby significantly improving the energy density of the lithium-ion battery. Meanwhile, a comparison between Examples 1-25 and Comparative Example 2 shows that the cathode material in this application, while having a high delithiation rate, also exhibits a higher peak temperature for oxygen release. This indicates that the oxygen vacancies formed inside and on the surface of the cathode material reduce the activity of oxygen in the material. The Na doping in the lithium layer suppresses structural collapse under high delithiation conditions, thereby inhibiting oxygen release from the cathode material and improving its structural stability at high temperatures and voltages. This results in a lower float charge thickness expansion rate and a higher high-temperature storage capacity recovery rate for the lithium-ion battery. Furthermore, the cathode material in this application exhibits significantly reduced dI / dT and dW / dT, indicating that the cathode material in this application can suppress severe oxygen release, thus demonstrating superior structural stability at high temperatures and voltages.

[0105]

[0106]

[0107] Examples 26-40

[0108] The difference from Example 1 is that the electrolyte was prepared as follows: In a dry argon atmosphere, additives were added to a solvent composed of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (PC∶EC∶DEC weight ratio 1∶1∶1) according to Table 2, and then LiPF6 was added and mixed evenly to obtain the electrolyte. The contents of the additives and LiPF6 are based on the total weight of the electrolyte, and the mass concentration of LiPF6 is 12.5%.

[0109] Table 2

[0110]

[0111] A comparison of Examples 26-40 in Table 2 with Example 1 shows that adding sulfur-containing oxygen double bond compounds and / or polynitrile compounds to the electrolyte can further improve the high-temperature storage capacity recovery rate of lithium-ion batteries. This is likely because sulfur-containing oxygen double bond compounds can form an oxidation-resistant protective film on the surface of the cathode material, and the abundant sulfur can stabilize high-valence transition metals in the charged state, thereby better suppressing oxygen release from the cathode material surface and the oxidative decomposition of the electrolyte. Polynitrile compounds can complex with transition metals on the surface of the cathode active material, stabilizing transition metals such as nickel, cobalt, and manganese on the cathode material surface, suppressing oxygen release from the cathode material surface, and thus improving the structural stability of the cathode material under high-temperature storage.

[0112] While some exemplary embodiments of this application have been described and illustrated, this application is not limited to the disclosed embodiments. Those skilled in the art will recognize that modifications and changes can be made to the described embodiments without departing from the spirit and principles of this application, and such modifications and changes also fall within the scope of protection of this application.

Claims

1. A positive electrode material, characterized in that, An electrode comprising the aforementioned positive electrode material is assembled with a lithium sheet to form a coin cell. When the coin cell is charged to 4.4V, the delithiation rate of the positive electrode material is above 91%. In TG-MS testing, the strongest oxygen release peak of the positive electrode material in the range of 100℃ to 500℃ is above 250℃. The positive electrode material comprises a lithium transition metal composite oxide, which comprises element T and optionally element Q. Element T comprises at least one of Ni, Co, or Mn, and 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 also comprises element Na, and the molar percentage of Na is 3% to 15% based on the total molar amount of element T and element Q.

2. The cathode material according to claim 1, characterized in that, When the coin cell is charged to 4.4V, based on a mass of 50mg of the cathode material, the oxygen ion current intensity of the cathode material in TG-MS testing is IA / 50mg, and the temperature is T℃. Specifically, within the temperature range of 100℃ to 500℃, the differential of I with respect to T, dI / dT, is less than or equal to 3×10⁻⁶. -13 .

3. The cathode material according to claim 1, characterized in that, When the coin cell is charged to 4.4V, based on the mass of 50mg of the cathode material, the heat release of the cathode material in the TG-DSC test is W mW / 50mg, and the temperature is T℃, wherein, in the range of 100℃ to 500℃, the differential of W with respect to T, dW / dT, is less than or equal to 0.

01.

4. The cathode material according to claim 1, characterized in that, An electrode containing the positive electrode material is assembled with a lithium sheet to form a coin cell. When the coin cell is charged and discharged at a current of 0.1C in the voltage range of 3.0V 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.

5. The positive electrode material according to claim 4, characterized in that, The peak voltage of the first oxidation peak is Vo1, the peak voltage of the first reduction peak is Vr1, and |Vo1-Vr1|≤0.3V.

6. The cathode material according to claim 4, characterized in that, The capacity-voltage differential dQ / dV curve has a second oxidation peak and a second reduction peak in the range of 3.6V to 4.0V. The peak voltage of the second oxidation peak is Vo2, the peak voltage of the second reduction peak is Vr2, and |Vo2-Vr2|≤0.3V.

7. The cathode material according to claim 1, characterized in that, The lithium transition metal composite oxide satisfies at least one of the following conditions: (1) Based on the total molar amount of element T, the molar percentage of Ni is 30% to 70%; (2) Based on the total molar amount of element T, the molar percentage of Mn is 0% to 70%; (3) Based on the total molar amount of element T, the molar percentage of Co is 0% to 50%; (4) Based on the total molar amount of the elements T and Q, the molar percentage of the element T is 90% to 100%, and the molar percentage of the element Q is 0% to 10%. (5) The lithium transition metal composite oxide further includes element R, which includes at least one of F, Cl, Br, I or N, and the molar percentage of element R is 0.1% to 10% based on the total molar amount of element T and element Q. (6) In the lithium transition metal composite oxide, the ratio of the molar amount of Li to the total molar amount of T and Q is 0.5 to 1.

1. (7) The lithium transition metal composite oxide has a layered crystal structure; (8) The lithium transition metal composite oxide includes Li x1 Na x2 Ni y1 Mn y2 Co y3 Q 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 element R includes at least one of F, Cl, Br, I or N.

8. An electrochemical device, characterized in that, The electrochemical device includes a positive electrode, which comprises the positive electrode material according to any one of claims 1 to 7.

9. The electrochemical device according to claim 8, characterized in that, The electrochemical device further includes an electrolyte, wherein the electrolyte contains an additive, the additive comprising at least one of a sulfur-oxygen double bond compound or a polynitrile compound, and the electrolyte satisfies at least one of the following conditions: (1) The sulfur-containing oxygen double bond compound includes at least one of 1,3-propanesulfonyl lactone, vinyl sulfate, 2,4-butanesulfonyl lactone, 1,4-butanesulfonyl lactone, methylene disulfonate, 1,3-propane disulfonic anhydride, 4-methyl ethylene sulfate or pentaerythritol bicyclic sulfate. (2) Based on the mass of the electrolyte, the mass percentage of the sulfur-containing oxygen double bond compound is 0.1% to 5%; (3) The polynitrile compound includes at least one of butadionitrile, glutaronitrile, adiponitrile, heptaonitrile, octadionitrile, nonadionitrile, sebaconitrile, methylglutaronitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3,5-pentanetricarbony, 1,3,6-hexanetrionitrile or 1,2,3-tris(2-cyanoethoxy)propane; (4) Based on the mass of the electrolyte, the mass percentage of the polynitrile compound is 1% to 10%.

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

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