Positive electrode material, electrochemical device and electronic device

Abstract

The present application relates to a positive electrode material, an electrochemical device, and an electronic device, the positive electrode material comprising a lithium transition metal composite oxide, the lithium transition metal composite oxide comprising an element Li, an element Na, and an element T, the element T comprising at least one of Ni, Co, or Mn; an electrode comprising the positive electrode material and a lithium sheet are assembled into a button cell, when the button cell is charged to 4.5 V at a current of 0.04 C within a voltage range of 2.8 V to 4.5 V, the molar ratio of Li element to T element in the lithium transition metal composite oxide is w1, and w1 is smaller than or equal to 0.2. The positive electrode material disclosed by the invention has relatively low lithium content in a charging state, so that the utilization rate of lithium ions in the material can be greatly improved, and the energy density of an electrochemical device is improved.

Description

Positive electrode material, electrochemical device and electronic device Technical Field

[0001] The present application relates to the field of energy storage, and in particular to a positive electrode material, an electrochemical device, and an electronic device. Background Art

[0002] With the increasing popularity of consumer electronics such as laptops, mobile phones, tablets, power banks, and drones, the requirements for batteries inside them are becoming increasingly stringent. For example, batteries must not only be lightweight but also have high capacity and a long operating life. Lithium-ion batteries, with their outstanding advantages such as high energy density, high safety, no memory effect, and long operating life, have become the mainstream in the market.

[0003] For traditional nickel-containing cathode materials, a large number of lithium ions are unable to participate in the extraction / insertion process during charge and discharge. Even a significant increase in voltage cannot completely extract the lithium ions in the cathode material. This is because the layered cathode material requires lithium ions to support the layered structure. Therefore, the low lithium ion utilization rate in traditional cathode materials significantly increases the cost of battery use and results in a huge waste of resources.

[0004] Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the first aspect of the present application provides a positive electrode material, which includes a lithium transition metal composite oxide, and the lithium transition metal composite oxide includes Li element, Na element and T element, and the T element includes at least one of Ni, Co or Mn; an electrode including the positive electrode material and a lithium sheet are assembled into a button battery, and when the button battery is charged to 4.5V with a current of 0.04C in the voltage range of 2.8V to 4.5V, the molar ratio of Li element to T element in the lithium transition metal composite oxide is w1, satisfying: w1≤0.2.

[0006] The inventors of the present application have discovered that by introducing Na element doping into the lithium layer of the positive electrode material through an element doping method, and regulating the oxygen defects inside the material through synthetic means, a layered positive electrode material with an extremely low lithium content in the charged state can be obtained. At the same time, introducing oxygen defects inside the material can activate the redox properties of the transition metal, which is beneficial to improving the energy density of the positive electrode material. Since the sodium ions doped in the lithium layer play a role in supporting the layered structure of the positive electrode material, the positive electrode material of the present application can maintain the stability of the material structure in a highly delithiated state. At the same time, doping the lithium layer with Na elements having a larger ionic radius can increase the lithium interlayer spacing, thereby improving the kinetic properties of the material. In addition, the oxygen vacancies formed on the surface of the positive electrode material of the present application can reduce the activity of oxygen on the surface of the material and stabilize the outer oxygen ions of the positive electrode material, thereby improving the cycle performance of the material.

[0007] According to some embodiments of the present application, in the initial state of the positive electrode material, the molar ratio of the Li element to the T element in the lithium transition metal composite oxide is w2, and the molar ratio of the Na element to the T element is w3. In some embodiments, 0.55 ≤ w2 ≤ 0.9. In some embodiments, 0.0005 ≤ w3 ≤ 0.1. In some embodiments, 0.6 ≤ w2 + w3 ≤ 1.

[0008] In some embodiments, w1 / w2≤24%, which indicates that lithium ions in the positive electrode material can be fully released during charging, thereby improving the utilization rate of lithium ions in the positive electrode material.

[0009] According to some embodiments of the present application, an electrode including the positive electrode material is assembled with a lithium sheet into a button battery. When the button battery is charged to 4.5V with a current of 0.04C in a voltage range of 2.8V to 4.5V, the molar ratio of the Na element to the T element in the lithium transition metal composite oxide is w4, 0.0005≤w4≤0.1.

[0010] In some embodiments, 0.85≤w4 / w3≤1.1. This indicates that the positive electrode material has good structural stability in a charged state, thereby improving the cycle performance of the electrochemical device.

[0011] According to some embodiments of the present application, an electrode comprising the positive electrode material is assembled with a lithium sheet into a button cell. When the button cell is discharged to 2.8 V at a current of 0.04 C within a voltage range of 2.8 V to 4.5 V, the molar ratio of the Na element to the T element in the lithium transition metal composite oxide is w5. In some embodiments, 0.55 ≤ w5 ≤ 0.85.

[0012] In some embodiments, w1 / w5 is ≤ 25.5%, indicating that lithium ions in the positive electrode material can be fully and reversibly extracted and inserted during the charge and discharge process, thereby improving the utilization rate of lithium ions in the positive electrode material and enhancing the cycle performance of the electrochemical device.

[0013] According to some embodiments of the present application, the molar ratio of Ni element to T element in the lithium transition metal composite oxide is 0.3 to 0.7.

[0014] According to some embodiments of the present application, the lithium transition metal composite oxide further includes an M element, and the M element includes at least one of B, Mg, Al, Si, P, S, Ti, Cr, Fe, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb, V, Nb, La, Ge, K, Ca, Sr, Ca, Ba, Ta, Hf or Ce, and the molar ratio of the M element to the T element in the lithium transition metal composite oxide is 0.01 to 0.2.

[0015] According to some embodiments of the present application, the lithium transition metal composite oxide has a layered crystal structure.

[0016] According to some embodiments of the present application, the positive electrode material is in an initial state, and the lithium transition metal composite oxide satisfies the general formula Li x Na y (Ni a Co b Mn c M d )O 2±e R e , wherein, 0.55≤x / (a+b+c)≤0.9, 0.0005≤y / (a+b+c) ≤0.1; 0.3≤a / (a+b+c)≤0.7, 0≤b / (a+b+c)≤0.7, 0≤c / (a+b+c)≤0.7, 0≤d / (a+b+c)≤0.2, 0≤e≤0.1, M includes at least one of B, Mg, Al, Si, P, S, Ti, Cr, Fe, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb, V, Nb, La, Ge, K, Ca, Sr, Ca, Ba, Ta, Hf or Ce, and R includes at least one of F, Cl, Br, I or N.

[0017] According to some embodiments of the present application, an electrode including the positive electrode material is assembled with a lithium sheet into a button battery. When the button battery is charged and discharged at a current of 0.04C in a voltage range of 2.8V to 4.5V, 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 4.5V and a second oxidation peak and a second reduction peak in the range of 3.6V to 4.0V.

[0018] According to some embodiments of the present application, based on the mass of the positive electrode material, the peak height of the first oxidation peak is 500 mAh / g / V to 2000 mAh / g / V.

[0019] According to some embodiments of the present application, based on the mass of the positive electrode material, the absolute value of the peak height of the first reduction peak is 500 mAh / g / V to 2000 mAh / g / V.

[0020] According to some embodiments of the present application, the peak voltage of the first oxidation peak is Vo1, the peak voltage of the first reduction peak is Vr1, and |Vo1-Vr1|≤0.2V.

[0021] According to some embodiments of the present application, an electrode including the positive electrode material is assembled with a lithium sheet into a button cell. When the button cell is charged and discharged at a current of 0.04C in a voltage range of 2.8V to 4.5V, the discharge curve of the obtained voltage-capacity curve has a plateau in the range of 4.2V to 4.5V. In some embodiments, the capacity of the discharge curve in the range of 4.2V to 4.5V is Q1, and the total capacity in the range of 2.8V to 4.5V is Qt, satisfying the following: 0.15≤Q1 / Qt≤0.35.

[0022] In a second aspect, the present application provides an electrochemical device comprising a positive electrode plate, wherein the positive electrode plate comprises the positive electrode material described in the first aspect of the present application.

[0023] According to some embodiments of the present application, when the electrochemical device is in a fully charged state, the peak position of the (003) peak in the X-ray diffraction spectrum of the lithium transition metal composite oxide is in the range of 18° to 19°.

[0024] In a third aspect, the present application provides an electronic device comprising the electrochemical device described in the second aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG1 shows the charge and discharge curves of the button batteries of Comparative Example 1 and Example 6.

[0026] FIG2 shows the capacity-voltage differential curves of the button batteries of Comparative Example 1 and Example 6.

[0027] FIG3 shows the X-ray diffraction (XRD) patterns of the electrodes of Comparative Example 1 and Example 6 in the fully charged state. DETAILED DESCRIPTION

[0028] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of this application, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of this application. The embodiments of this application should not be interpreted as limiting this application.

[0029] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0030] In the description herein, unless otherwise specified, “above” and “below” include the number itself.

[0031] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0032] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A 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.

[0033] In the context of this application, the “initial state” of the positive electrode material refers to the state of the positive electrode material when it is initially synthesized and has not yet undergone a charging process.

[0034] 1. Cathode Materials

[0035] In a first aspect, the present application provides a positive electrode material, which includes a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide includes Li element, Na element and T element, and the T element includes at least one of Ni, Co or Mn; an electrode including the positive electrode material and a lithium sheet are assembled into a button battery, and when the button battery is charged to 4.5V with a current of 0.04C in a voltage range of 2.8V to 4.5V, the molar ratio of Li element to T element in the lithium transition metal composite oxide is w1, satisfying: w1≤0.2.

[0036] In some embodiments, in the initial state of the positive electrode material, the molar ratio of Li element to T element in the lithium transition metal composite oxide is w2, the molar ratio of Na element to T element is w3, 0.55≤w2≤0.9, w2 is, for example, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90 or any range therebetween; in some embodiments, 0.0005≤w3≤0.1, w3 is, for example, 0.0005, 0.001, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.56, 0.57, 0.58, 0.5 1 or any range therebetween; in some embodiments, 0.6≤w2+w3≤1, for example, the value of w2+w3 can be 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.0 or any range therebetween; in some embodiments, w1 / w2≤24%, for example, the value of w1 / w2 can be 24%, 20%, 18%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.8%, 0.6%, 0.4% or any range therebetween.

[0037] In some embodiments, an electrode comprising the positive electrode material and a lithium sheet are assembled into a button battery. When the button battery is charged to 4.5V at a current of 0.04C in a voltage range of 2.8V to 4.5V, the molar ratio of the Na element to the T element in the lithium transition metal composite oxide is w4, 0.0005≤w4≤0.1, and w4 is, for example, 0.0005, 0.001, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or any range therebetween; in some embodiments, 0.85≤w4 / w3≤1.1, the value of w4 / w3 can be 0.85, 0.86, 0.88, 0.90, 0.92, 0.94, 0.96, 0.98, 1.0, 1.02, 1.04, 1.06, 1.08, 1.1 or any range therebetween.

[0038] An electrode comprising the positive electrode material and a lithium sheet are assembled into a button battery, and when the button battery is discharged to 2.8V at a current of 0.04C in a voltage range of 2.8V to 4.5V, the molar ratio of the Na element to the T element in the lithium transition metal composite oxide is w5, 0.55≤w5≤0.85, and w5 is, for example, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85 or any range therebetween; in some embodiments, w1 / w5≤25.5%, for example, the value of w1 / w5 can be 25.5%, 25%, 24%, 20%, 18%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.8%, 0.6%, 0.4% or any range therebetween.

[0039] In some embodiments, the molar ratio of Ni element to T element in the lithium transition metal composite oxide is 0.3 to 0.7, for example, 0.30, 0.35, 0.4, 0.45, 0.5, 0.55, 0.60, 0.65, 0.7 or any range therebetween.

[0040] In some embodiments, the lithium transition metal composite oxide further includes an M element, and the M element includes at least one of B, Mg, Al, Si, P, S, Ti, Cr, Fe, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb, V, Nb, La, Ge, K, Ca, Sr, Ca, Ba, Ta, Hf or Ce, and the molar ratio of the M element to the T element in the lithium transition metal composite oxide is 0.01 to 0.2, for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20 or any range therebetween.

[0041] In some embodiments, the lithium transition metal composite oxide has a layered crystal structure. In some embodiments, the positive electrode material is in an initial state, and the lithium transition metal composite oxide satisfies the general formula Li x Na y (Ni a Co b Mn c M d )O 2±e R e, wherein, 0.55≤x / (a+b+c)≤0.9, 0.0005≤y / (a+b+c)≤0.1; 0.3≤a / (a+b+c)≤0.7, 0≤b / (a+b+c)≤0.7, 0≤c / (a+b+c)≤0.7, 0≤d / (a+b+c)≤0.2, 0≤e≤0.1, M includes at least one of B, Mg, Al, Si, P, S, Ti, Cr, Fe, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb, V, Nb, La, Ge, K, Ca, Sr, Ca, Ba, Ta, Hf or Ce, and R includes at least one of F, Cl, Br, I or N.

[0042] In some embodiments, an electrode comprising the positive electrode material is assembled with a lithium sheet into a button battery. When the button battery is charged and discharged at a current of 0.04C in a voltage range of 2.8V to 4.5V, a capacity-voltage differential dQ / dV curve obtained has a first oxidation peak and a first reduction peak in the range of 4.2V to 4.5V, and a second oxidation peak and a second reduction peak in the range of 3.6V to 4.0V.

[0043] In some embodiments, based on the mass of the positive electrode material, the peak height of the first oxidation peak is 500mAh / g / V to 2000mAh / g / V. For example, the peak height of the first oxidation peak can be 500mAh / g / V, 600mAh / g / V, 700mAh / g / V, 800mAh / g / V, 900mAh / g / V, 1000mAh / g / V, 1100mAh / g / V, 1200mAh / g / V, 1300mAh / g / V, 1400mAh / g / V, 1500mAh / g / V, 1800mAh / g / V, 2000mAh / g / V or any range therebetween.

[0044] In some embodiments, based on the mass of the positive electrode material, the absolute value of the peak height of the first reduction peak is 500mAh / g / V to 2000mAh / g / V. For example, the peak height of the first reduction peak can be 500mAh / g / V, 600mAh / g / V, 700mAh / g / V, 800mAh / g / V, 900mAh / g / V, 1000mAh / g / V, 1100mAh / g / V, 1200mAh / g / V, 1300mAh / g / V, 1400mAh / g / V, 1500mAh / g / V, 1800mAh / g / V, 2000mAh / g / V or any range therebetween.

[0045] In some embodiments, the peak voltage of the first oxidation peak is Vo1, the peak voltage of the first reduction peak is Vr1, and |Vo1-Vr1|≤0.2 V. In some embodiments, the value of |Vo1-Vr1| is, for example, 0.05 V, 0.06 V, 0.07 V, 0.08 V, 0.09 V, 0.10 V, 0.11 V, 0.12 V, 0.13 V, 0.14 V, 0.15 V, 0.16 V, 0.17 V, 0.18 V, 0.19 V, 0.20 V, or any range therebetween.

[0046] In some embodiments, an electrode comprising the positive electrode material is assembled with a lithium sheet into a button battery. When the button battery is charged and discharged at a current of 0.04C in a voltage range of 2.8V to 4.5V, the discharge curve in the obtained voltage-capacity curve has a platform in the range of 4.2V to 4.5V. In some embodiments, the capacity of the discharge curve in the range of 4.2V to 4.5V is Q1, and the total capacity in the range of 3.0V to 4.5V is Qt, satisfying: 0.15≤Q1 / Qt≤0.35. In some embodiments, the value of Q1 / Qt is, for example, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35 or any range therebetween.

[0047] 2. Electrochemical Device

[0048] The electrochemical device provided in the present application includes a positive electrode plate, and the positive electrode includes the positive electrode material described in the first aspect of the present application.

[0049] In some embodiments, the positive electrode plate 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, polyvinyl fluoride, polytetrafluoroethylene, polyvinylidene fluoride or vinylidene 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.

[0050] In some embodiments, the positive electrode further includes 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, aluminum foil can be used. The composite current collector can be formed by forming a metal material on a polymer substrate.

[0051] In some embodiments, the electrochemical device further comprises a negative electrode.

[0052] 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, a silicon oxide, a silicon carbon compound, or a silicon alloy. In some embodiments, the negative electrode active material layer contains a binder. In some embodiments, the binder includes at least one of polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, a polyacrylate, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl ether, or styrene-butadiene rubber. In some embodiments, the negative electrode active material layer further includes a conductive material to improve the conductivity of the electrode. In some embodiments, the conductive material includes at least one of conductive carbon black, acetylene black, carbon nanotubes, Ketjen black, or graphene.

[0053] In some embodiments, the electrochemical device further comprises an electrolyte or a solid electrolyte.

[0054] In some embodiments, the electrolyte that can be used in the embodiments of the present application can be an electrolyte known in the prior art.

[0055] In some embodiments, the electrolyte includes an organic solvent and a lithium salt. In some embodiments, the organic solvent includes, 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 includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate) LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB).

[0056] In some embodiments, in the electrochemical device, an isolation membrane is provided between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the isolation membrane used in the embodiments of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the isolation membrane includes a polymer or inorganic substance formed from a material that is stable to the electrolyte of the present application. For example, the isolation membrane may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Specifically, 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 selected. A surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. The inorganic layer includes inorganic particles and a binder, wherein the inorganic particles include at least one of aluminum oxide, 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 vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, a polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene, or polyhexafluoropropylene. The polymer layer includes a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, a polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or a copolymer of vinylidene fluoride and hexafluoropropylene.

[0057] In some embodiments, the electrochemical device of the present 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, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0058] 3. Electronic Devices

[0059] The electronic device of the present application may be any device using the electrochemical device according to the second aspect of the present application.

[0060] In some embodiments, the electronic device includes, but is not limited to: a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery or a lithium-ion capacitor, etc.

[0061] Examples and Comparative Examples

[0062] Examples 1-21

[0063] Preparation of positive electrode materials

[0064] (1) preparing a mixed solution containing NiSO4 and MnSO4 according to the element molar ratio of Ni:Mn=50:50, mixing the mixed solution with a precipitant (NaOH solution) and a complexing agent (ammonia solution) for reaction, controlling the reaction time to 60 hours, the ammonia concentration to 1 mol / L, and the pH to 12.2 to obtain a nickel-manganese precursor TM(OH)2 (TM represents Ni / Mn) with an average particle size Dv50 of 11 μm;

[0065] (2) The nickel-manganese precursor, lithium carbonate and sodium carbonate are mixed according to the molar ratio of Li element to transition metal element T (Ni+Mn) shown in Table 1. Li / (n Mn +n Ni ) and the molar ratio of Na element to element T n Na / (n Mn +n Ni ) were ground and mixed uniformly, and then calcined at 800°C in a mixed atmosphere of air and ammonia for 20 hours. The volume percentages of air and ammonia in the mixed atmosphere, based on the total volume of the mixed atmosphere, were selected according to Table 1. The mixture was cooled to room temperature at a rate of 3°C / min. The powder was crushed and sieved, washed with deionized water, and vacuum filtered. A dry powder was obtained by vacuum drying at 120°C for 24 hours. The powder was calcined under a nitrogen atmosphere for 6 hours at the calcination temperatures shown in Table 1. The powder was then quenched to room temperature at a cooling rate of 10°C / min. Finally, the positive electrode material was obtained after crushing and sieving.

[0066] Comparative Example 1

[0067] The difference from Example 1 is that the positive electrode material is prepared according to the following steps:

[0068] (1) A mixed solution containing NiSO4 and MnSO4 was prepared according to the element molar ratio of Ni:Mn=50:50, and the mixed solution was mixed with a precipitant (NaOH solution) and a complexing agent (ammonia water) for reaction. The reaction time was controlled to be 60 hours, the ammonia concentration was 1 mol / L, and the pH was controlled to be 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;

[0069] (2) The nickel-manganese precursor and lithium carbonate were ground and mixed uniformly at a molar ratio of Li:(Ni+Mn) of 1.05:1, and then calcined at 800°C in an air atmosphere for 20 hours, cooled to room temperature at a rate of 10°C / min, and finally crushed and sieved to obtain a positive electrode material.

[0070] Production of button batteries

[0071] - Mix the positive electrode material, binder polyvinylidene fluoride (PVDF), and conductive carbon black (Super P) in a weight ratio of 90:5:5, add them to N-methylpyrrolidone (NMP), mix them evenly, and prepare a positive electrode slurry with a solid content of 0.7;

[0072] - The mixed positive electrode slurry is evenly coated on the aluminum foil with a coating thickness of 40 μm on one side; after drying, it is rolled to form the required electrode, wherein the electrode coating surface density is 14 mg / cm 2 , after drying, the positive electrode sheet is obtained, and then punched into 14 mm discs to obtain a single-sided positive electrode sheet;

[0073] - Punch the separator into 18 mm discs; the negative electrode used is a lithium metal sheet with a diameter of 18 mm; add LiPF6 to a solvent mixed with propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (PC:EC:DEC weight ratio of 1:1:1) and mix well to obtain an electrolyte; the mass concentration of LiPF6 based on the total weight of the electrolyte is 12.5%; move the positive electrode sheet, separator paper, negative electrode sheet (lithium sheet), electrolyte, battery case and other accessories into a glove box (the water content must be less than 11 ppm);

[0074] Assemble the battery and inject the electrolyte in the following stacking order from bottom to top: negative electrode shell > flat pad + appropriate amount of electrolyte > metal lithium sheet + appropriate amount of electrolyte > a layer of separator paper + appropriate amount of electrolyte > positive electrode sheet + appropriate amount of electrolyte > flat pad + appropriate amount of electrolyte > spring > positive electrode shell; package on a packaging machine to obtain a button battery.

[0075] Production of lithium-ion soft-pack batteries

[0076] Preparation of the positive electrode: The positive electrode material, binder polyvinylidene fluoride (PVDF), and conductive agent conductive carbon black (Super P) in a weight ratio of 96:2:2 are mixed, added to N-methylpyrrolidone (NMP), mixed evenly, and prepared into a positive electrode slurry with a solid content of 0.7; the positive electrode slurry is evenly coated on one side of the aluminum foil, and after drying, the above steps are repeated on the other side of the aluminum foil to obtain a double-sided coated positive electrode sheet; after cold pressing, cutting, and welding the tabs, the positive electrode is obtained.

[0077] 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 to form a negative electrode slurry. This negative electrode slurry was evenly coated on one surface of a copper foil. After drying, the above steps were repeated on the other surface of the copper foil to obtain a double-sided coated negative electrode sheet. The negative electrode was then cold pressed, cut into pieces, and the tabs were welded to obtain the negative electrode.

[0078] Preparation of electrolyte: Under a dry argon environment, LiPF6 was added to a solvent mixed with propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (PC:EC:DEC weight ratio of 1:1:1) and mixed evenly to obtain an electrolyte, wherein the mass concentration of LiPF6 based on the total weight of the electrolyte was 12.5%.

[0079] Preparation of isolation membrane: Polyethylene (PE) porous polymer film is used as the isolation membrane.

[0080] Assembly of a lithium-ion soft-pack battery: The positive electrode, separator, and negative electrode are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting bare cell is then placed in an aluminum-plastic film wrapper, electrolyte is injected, and the battery is encapsulated. After formation, degassing, and trimming, the lithium-ion soft-pack battery is completed.

[0081] Table 1 “ / ” means it does not exist.

[0082] Test Method

[0083] 1. X-ray diffraction test

[0084] After the lithium-ion battery was fully discharged, the positive electrode was disassembled and cleaned by soaking in dimethyl carbonate (DMC). After drying, it was tested using an X-ray powder diffractometer (XRD, instrument model: Bruker D8ADVANCE, target material: Cu Kα; voltage and current: 40 kV / 40 mA, scanning angle range: 10° to 70°).

[0085] 2. Element content test

[0086] The positive electrode material sample was dissolved in a mixed solvent (for example, 0.4 g of the sample was dissolved in a mixed solvent of 10 ml of aqua regia (nitric acid and hydrochloric acid mixed in a ratio of 1:1) and 2 ml of HF), the volume was fixed to 100 mL, and the content of each element in the positive electrode material was obtained by inductively coupled plasma spectrometry (ICP) testing.

[0087] 3. Cycle number test when the cycle capacity retention rate reaches 80% at 25℃: At 25℃, the lithium-ion soft-pack battery is charged to 4.35V with a constant current of 1.5C charging current to make the lithium-ion battery reach a fully charged state, and then discharged with a constant current of 4C discharge current to a voltage of 2.8V. The discharge capacity at this time is recorded as the first discharge capacity. Repeat the above charge and discharge cycle until the cycle capacity retention rate reaches 80%. Record the number of cycles at this time. Cycle capacity retention rate = discharge capacity of the Nth cycle / first discharge capacity.

[0088] 4. Cycle number test when the cycle capacity retention rate reaches 80% at 45℃: At 45℃, the lithium-ion soft-pack battery is charged to 4.35V with a constant current of 1.5C charging current to make the lithium-ion battery reach a fully charged state, and then discharged with a constant current of 4C discharge current to a voltage of 2.8V. The discharge capacity at this time is recorded as the first discharge capacity. Repeat the above charge and discharge cycle until the cycle capacity retention rate reaches 80%. Record the number of cycles at this time. Cycle capacity retention rate = discharge capacity of the Nth cycle / first discharge capacity.

[0089] Test results

[0090] The test results of the button cells and lithium-ion soft-pack batteries obtained in various embodiments and comparative examples are shown in Table 2.

[0091] From the comparison of Examples 1-21 and Comparative Example 1 in Table 2, it can be seen that for the positive electrode materials of the embodiments of the present application, when the button battery is charged to 4.5V, the molar ratio w1 of the Li element to the T element in the positive electrode material satisfies: w1≤0.2. It can be seen that the positive electrode material of the present application has a significantly reduced lithium content in the charged state, thereby greatly improving the utilization rate of lithium ions in the material. And the lithium-ion battery of the embodiment of the present application also has excellent cycle performance. The possible reason is that, since the sodium ions doped in the lithium layer play a role in supporting the layered structure of the positive electrode material, the positive electrode material of the present application can maintain the stability of the material structure in a highly delithiated state. At the same time, the oxygen vacancies formed on the surface of the positive electrode material of the present application can reduce the activity of oxygen on the surface of the material and stabilize the outer oxygen ions of the positive electrode material, thereby improving the cycle performance of the material.

[0092] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those skilled in the art will recognize that modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims, and these modifications and changes also fall within the scope of protection of the present application.

Claims

1. A positive electrode material, characterized in that: The positive electrode material includes a lithium transition metal composite oxide, which includes Li, Na and T elements, and the T element includes at least one of Ni, Co or Mn; an electrode including the positive electrode material and a lithium sheet are assembled into a button battery, and when the button battery is charged to 4.5V with a current of 0.04C in a voltage range of 2.8V to 4.5V, the molar ratio of the Li element to the T element in the lithium transition metal composite oxide is w1, satisfying: w1≤0.

2.

2. The positive electrode material according to claim 1, characterized in that In the initial state of the positive electrode material, the molar ratio of Li element to T element in the lithium transition metal composite oxide is w2, and the molar ratio of Na element to T element is w3, which satisfies at least one of the following conditions: (1) 0.55≤w2≤0.9; (2) 0.0005≤w3≤0.1; (3) 0.6≤w2+w3≤1; (4) w1 / w2≤24%.

3. The positive electrode material according to claim 2, characterized in that An electrode including the positive electrode material and a lithium sheet are assembled into a button battery. When the button battery is charged to 4.5 V at a current of 0.04 C in a voltage range of 2.8 V to 4.5 V, the molar ratio of the Na element to the T element in the lithium transition metal composite oxide is w4, satisfying at least one of the following conditions: (1) 0.0005≤w4≤0.1; (2) 0.85≤w4 / w3≤1.

1.

4. The positive electrode material according to claim 1, characterized in that An electrode including the positive electrode material and a lithium sheet are assembled into a button battery. When the button battery is discharged to 2.8 V at a current of 0.04 C in a voltage range of 2.8 V to 4.5 V, the molar ratio of the Na element to the T element in the lithium transition metal composite oxide is w5, which satisfies at least one of the following conditions: (1) 0.55≤w5≤0.85; (2) w1 / w5≤25.5%.

5. The positive electrode material according to claim 1, characterized in that The positive electrode material satisfies at least one of the following conditions: (1) The molar ratio of Ni element to T element in the lithium transition metal composite oxide is 0.3 to 0.7; (2) The lithium transition metal composite oxide further includes an M element, wherein the M element includes at least one of B, Mg, Al, Si, P, S, Ti, Cr, Fe, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb, V, Nb, La, Ge, K, Ca, Sr, Ca, Ba, Ta, Hf or Ce, and the molar ratio of the M element to the T element in the lithium transition metal composite oxide is 0.01 to 0.2; (3) In the initial state, the lithium transition metal composite oxide satisfies the general formula Li x Na y (Ni a Co b Mn c M d ) 2±e R e , wherein, 0.55≤x / (a+b+c)≤0.9, 0.0005≤y / (a+b+c)≤0.1; 0.3≤a / (a+b+c)≤0.7, 0≤b / (a+b+c)≤0.7, 0≤c / (a+b+c)≤0.7, 0≤d / (a+b+c)≤0.2, 0≤e≤0.1, M includes at least one of B, Mg, Al, Si, P, S, Ti, Cr, Fe, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb, V, Nb, La, Ge, K, Ca, Sr, Ca, Ba, Ta, Hf or Ce, and R includes at least one of F, Cl, Br, I or N.

6. The positive electrode material according to claim 1, characterized in that An electrode including the positive electrode material is assembled into a button battery with a lithium sheet. When the button battery is charged and discharged at a current of 0.04C in a voltage range of 2.8V to 4.5V, a capacity-voltage differential dQ / dV curve obtained has a first oxidation peak and a first reduction peak in the range of 4.2V to 4.5V and a second oxidation peak and a second reduction peak in the range of 3.6V to 4.0V.

7. The positive electrode material according to claim 6, characterized in that The positive electrode material satisfies at least one of the following conditions: (1) Based on the mass of the positive electrode material, the peak height of the first oxidation peak is 500 mAh / g / V to 2000 mAh / g / V; (2) Based on the mass of the positive electrode material, the absolute value of the peak height of the first reduction peak is 500 mAh / g / V to 2000 mAh / g / V; (3) The peak voltage of the first oxidation peak is Vo1, the peak voltage of the first reduction peak is Vr1, and |Vo1-Vr1|≤0.2V.

8. The positive electrode material according to claim 6, characterized in that The electrode including the positive electrode material and the lithium sheet are assembled into a button battery. When the button battery is charged and discharged at a current of 0.04C in a voltage range of 2.8V to 4.5V, the discharge curve in the obtained voltage-capacity curve satisfies at least one of the following conditions: (1) The discharge curve has a platform in the range of 4.2V to 4.5V; (2) The capacity of the discharge curve in the range of 4.2V to 4.5V is Q1, and the total capacity in the range of 2.8V to 4.5V is Qt, satisfying: 0.15≤Q1 / Qt≤0.

35.

9. An electrochemical device, characterized in that: The electrochemical device comprises a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 8.

10. The electrochemical device according to claim 9, characterized in that When the electrochemical device is in a fully charged state, the peak position of the (003) peak in the X-ray diffraction spectrum of the lithium transition metal composite oxide is in the range of 18° to 19°.

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

Images