A positive electrode lithium supplement material, a positive electrode sheet containing the material, and an electrochemical device

Abstract

The present application provides a cathode lithium supplement material, a cathode electrode sheet containing the material, and an electrochemical device. The cathode lithium supplement material includes: a matrix of xLi₂O·yM and carbon present on the matrix; wherein x > 0, 0.4x ≤ y ≤ 2x, and M includes at least one of Mn, Fe, Co, Ni, Cu, Cr, or V. The cathode lithium supplement material has strong chemical stability and can effectively improve the particle agglomeration phenomenon during the slurry mixing process. Applying the cathode lithium supplement material in the cathode electrode sheet can achieve the supplement of active lithium and effectively improve the energy density of the electrochemical device.

Description

Technical Field

[0001] The present application relates to the field of electrochemistry, and particularly to a cathode lithium supplement material, a cathode electrode sheet containing the material, and an electrochemical device. Background Art

[0002] Lithium ion secondary batteries have the advantages of large energy storage density, high open circuit voltage, low self-discharge rate, long cycle life, good safety, etc., and are widely used in various fields such as electric energy storage, mobile electronic devices, electric vehicles, and aerospace equipment. With the rapid development of mobile electronic devices and electric vehicles, the market has put forward higher and higher requirements for the energy density, cycle performance, and kinetic performance of lithium ion secondary batteries.

[0003] During the first charge and discharge process of lithium ion secondary batteries, a large amount of solid electrolyte interphase (SEI) will be generated on the surface of the negative electrode, consuming the limited lithium ions and electrolyte in the lithium ion secondary battery, resulting in irreversible capacity loss and reducing the energy density of the lithium ion secondary battery. In a battery using a graphite negative electrode, about 10% of the active lithium source will be consumed in the first cycle; when using high specific capacity negative electrode materials such as alloys (silicon, tin, etc.), oxides (silicon oxide, tin oxide, etc.), and amorphous carbon negative electrodes, the consumption of the active lithium source will be further aggravated. Therefore, a suitable lithium supplement method is particularly important for improving the energy density of lithium ion secondary batteries. Summary of the Invention

[0004] The purpose of the present application is to provide a cathode lithium supplement material, a cathode electrode sheet containing the material, and an electrochemical device to improve the energy density of the electrochemical device.

[0005] It should be noted that in the content of the present application, a lithium ion secondary battery is used as an example of the electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to lithium ion secondary batteries.

[0006] The specific technical solutions are as follows:

[0007] In the first aspect of the present application, a cathode lithium supplement material is provided, which includes a matrix of xLi2O·yM and carbon present on the matrix; wherein, x > 0, 0.4x ≤ y ≤ 2x, and M includes at least one of Mn, Fe, Co, Ni, Cu, Cr, or V.

[0008] In the matrix of xLi₂O·yM of the present application: x > 0, 0.4x ≤ y ≤ 2x; preferably 3 ≤ x ≤ 12, 0.5x ≤ y ≤ 1.6x. M may include at least one of Mn, Fe, Co, Ni, Cu, Cr, V, etc., and M preferably may include at least one of Mn, Fe, Co, Ni, etc. Among them, the valence state of M can be 0. Those skilled in the art can select x, y, and M according to actual needs to obtain a matrix of xLi₂O·yM that can achieve the purpose of the present application, such as including but not limited to any one of 4Li₂O·3Co, Li₂O·Co, 5Li₂O·4Co, 3Li₂O·2Fe, 7Li₂O·3Co·2Fe, 12Li₂O·3Co·2Fe·2V, 2Li₂O·Mn, Li₂O·Ni, etc. By limiting the above range, a matrix of xLi₂O·yM of the present application is obtained. During the first charging process of this matrix, a large amount of lithium ions can be extracted, and the specific capacity is very high, which can greatly improve the energy density of the lithium-ion secondary battery.

[0009] The inventors unexpectedly found that when there is carbon on the xLi₂O·yM matrix, it can not only effectively enhance the chemical stability of the xLi₂O·yM matrix, improve the stability of the positive electrode slurry, make it less likely to agglomerate, and be more convenient for the preparation, storage, and coating of the positive electrode slurry on the positive electrode plate, thereby improving the processing performance of the positive electrode slurry, but also can increase the energy density of the lithium-ion secondary battery. This may be because the chemical stability of Li₂O in the xLi₂O·yM matrix is poor, and it is extremely sensitive to moisture and CO₂ in the air, and is prone to reactions of Li₂O + H₂O = LiOH and Li₂O + CO₂ = Li₂CO₃ to produce surface "residual alkali" LiOH and Li₂CO₃. When there is carbon on the xLi₂O·yM matrix, it can inhibit the generation of LiOH and Li₂CO₃, and can act as a barrier layer to block the contact between the xLi₂O·yM matrix and the binder in the positive electrode slurry, improve the stability of the slurry, and ensure the specific capacity of Li₂O. In the present application, those skilled in the art should understand that the carbon existing on the xLi₂O·yM matrix can completely wrap the matrix surface or partially wrap the matrix surface. There is no special limitation in the present application, as long as the purpose of the present application can be achieved.

[0010] The positive electrode lithium supplement material of the present application undergoes a de-lithiation reaction of xLi₂O + M – 2xe - = MO x + 2xLi + during the first charging, playing a role in lithium supplementation. At the same time, since the positive electrode lithium supplement material is in the positive electrode, it is very difficult for the positive electrode potential to be low enough to occur MO x + 2xLi + + 2xe -=xLi2O+M reaction from 0V to 2V, so the active lithium will not be consumed in the subsequent discharge process, thereby achieving a net replenishment of the active lithium.

[0011] In general, the positive electrode lithium replenishment material provided in this application includes a matrix of xLi2O·yM and carbon present on the matrix. This positive electrode lithium replenishment material has a high specific capacity, good chemical stability, moderate conductivity, and no gas is generated during the charging and lithium replenishment process. It can effectively improve the particle agglomeration phenomenon during the slurry preparation process of the positive electrode slurry and improve the processing performance of the positive electrode slurry. Adding this positive electrode lithium replenishment material to the positive electrode plate can replenish the active lithium lost due to the formation of SEI, thereby further improving the energy density of the lithium-ion secondary battery.

[0012] In one embodiment of the present application, based on the total mass of the positive electrode lithium supplement material, the mass percentage of carbon is 0.5% to 3%. For example, the lower limit of the mass percentage of carbon may include the following values: 0.5% or 1%; the upper limit of the mass percentage of carbon may include the following values: 2%, 2.5% or 3%. Without being limited to any theory, if the mass percentage of carbon is too low (for example, less than 0.5%), it is difficult to enhance the chemical stability of the matrix of xLi2O·yM, and it is also difficult to act as a barrier layer to isolate the contact between the matrix of xLi2O·yM and the binder in the positive electrode slurry; if the mass percentage of carbon is too high (for example, higher than 3%), the impedance increases significantly, and the polarization increases accordingly, which seriously affects the actual specific capacity of the positive electrode lithium supplement material, and thus affects the effect of improving the energy density of the lithium ion secondary battery. By controlling the mass percentage of carbon in the positive electrode lithium supplement material within the above range, the stability of the positive electrode slurry can be effectively improved and the energy density of the lithium ion secondary battery can be improved.

[0013] In one embodiment of the present application, the first charge specific capacity of the positive electrode lithium supplement material is ≥450 mAh / g. This indicates that the positive electrode lithium supplement material has a high specific capacity and can release a large amount of lithium ions during the first charge to compensate for the loss of active lithium caused by SEI formation. During the first discharge, sufficient lithium ions are reinserted into the positive electrode active material, effectively improving the discharge specific capacity of the lithium-ion secondary battery, thereby improving the energy density of the lithium-ion secondary battery.

[0014] The second aspect of the present application provides a method for preparing the positive electrode lithium supplement material of the present application, which comprises the following steps:

[0015] (1) Naphthalene is dispersed in a solvent, lithium metal fragments or powder are slowly added, and a uniform reaction is performed to obtain a naphthalene-lithium solution;

[0016] (2) The oxide M a O b Slowly add the above-mentioned lithium naphthalene solution, stir to react evenly, filter and dry to obtain the xLi2O·yM matrix;

[0017] (3) Mix the above matrix with an inorganic carbon source by ball milling to disperse evenly and obtain a mixture;

[0018] (4) Calcinate the above mixture in an inert atmosphere to obtain the cathode lithium supplement material; wherein, the molar ratio of naphthalene to lithium metal is 1:(0.6 to 1), and the molar ratio of naphthalene to oxide M a O b is 1:(0.1 to 0.5), and the ratio of the molar amount of naphthalene to the mass of the inorganic carbon source is 1:(0.05 to 0.3) mol / g.

[0019] It should be noted that the above preparation method provided by this application is the preferred method for preparing the cathode lithium supplement material of this application. Those skilled in the art can also prepare the cathode lithium supplement material of this application according to other methods. This application has no special restrictions on this, as long as the purpose of this application can be achieved.

[0020] The method for preparing the cathode lithium supplement material provided by this application is a homogeneous reaction at room temperature. Compared with the conventional solid-phase sintering method, it has higher safety, more uniform and sufficient reaction, and the morphology and particles of the prepared product are controllable. The principle of this preparation method is simple, the operation is convenient, the effect is excellent, and it has good compatibility with the existing preparation process.

[0021] In an embodiment of this application, there is no special restriction on the type of solvent, as long as the purpose of this application can be achieved. For example, it can be an aprotic solvent, including at least one of tetrahydrofuran or ethylene glycol dimethyl ether, etc.

[0022] In an embodiment of this application, there is no special restriction on the type of oxide M a O b , as long as the purpose of this application can be achieved. For example, the oxide M a O b can include at least one of MnO, Mn2O3, MnO2, FeO, Fe2O3, CoO, Co2O3, Co3O4, NiO, Ni2O3, Cu2O, CuO, CrO, Cr2O3, CrO3, VO, V2O3, VO2 or V2O5, etc.

[0023] In an embodiment of this application, there is no special restriction on the type of inorganic carbon source, as long as the purpose of this application can be achieved. For example, the inorganic carbon source can include at least one of carbon black, carbon gel, Ketjen black, acetylene black, carbon nanotubes or graphene, etc.

[0024] In an embodiment of the present application, there are no specific limitations on the temperature and time of calcination in step (4), as long as the purpose of the present application can be achieved. For example, the calcination temperature can be 600°C to 700°C, and the calcination time can be 4h to 8h.

[0025] The third aspect of the present application provides a positive electrode sheet, including a positive electrode lithium supplement material, which is the positive electrode lithium supplement material described in any of the above embodiments. Applying the positive electrode lithium supplement material of the present application to the positive electrode sheet can effectively supplement active lithium and improve the energy density of the lithium-ion secondary battery.

[0026] The positive electrode sheet in the present application is not particularly limited, as long as the purpose of the present application can be achieved. For example, the positive electrode sheet generally includes a positive electrode current collector and a positive electrode active material layer. Among them, the positive electrode current collector is not particularly limited, as long as the purpose of the present application can be achieved. For example, it can include aluminum foil, aluminum alloy foil, or composite current collector, etc. The positive electrode active material layer includes a positive electrode active material and a positive electrode lithium supplement material. The type of the positive electrode active material is not particularly limited, as long as the purpose of the present application can be achieved. For example, it can include at least one of lithium nickel cobalt manganate (811, 622, 523, 111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate, lithium manganate, lithium manganese iron phosphate, or lithium titanate. The positive electrode lithium supplement material is at least one of the positive electrode lithium supplement materials provided by the present application. In the present application, the thicknesses of the positive electrode current collector and the positive electrode active material layer are not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5μm to 20μm, preferably 6μm to 18μm, and more preferably 8μm to 16μm. The thickness of the positive electrode material layer is 30μm to 120μm. In the present application, the positive electrode active material layer can be disposed on one surface (the first surface) in the thickness direction of the positive electrode current collector, or can be disposed on two surfaces (the first surface and the second surface) in the thickness direction of the positive electrode current collector. It should be noted that the "surface" here can be the entire area of the positive electrode current collector or a partial area of the positive electrode current collector, which is not particularly limited in the present application, as long as the purpose of the present application can be achieved. Optionally, the positive electrode sheet may further include a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder.

[0027] In an embodiment of the present application, based on the total mass of the positive electrode active material layer, the mass percentage of the positive electrode lithium supplement material can be 1% to 10%, preferably 3% to 10%. For example, the mass percentage of the positive electrode lithium supplement material can include: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc. By controlling the content of the positive electrode lithium supplement material in the positive electrode active material layer within the above range, the positive electrode sheet has good structural stability, and the capacity loss and volume change caused by the delithiation of the positive electrode lithium supplement material can be reduced. Controlling the mass percentage of the positive electrode lithium supplement material within the above preferred range can enable the positive electrode sheet to have better structural stability and also maximize the capacity of the battery.

[0028] The present application does not particularly limit the addition method of the positive electrode lithium supplement material. Those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved. For example, the positive electrode lithium supplement material can be directly added to the slurry during the slurry mixing process of the positive electrode material to form a positive electrode slurry containing the positive electrode lithium supplement material of the present application, and then coated on the surface of the positive electrode current collector. It can also be that a thin film of the positive electrode lithium supplement material is pre-deposited on the surface of the positive electrode current collector. It can also be that after the coating of the positive electrode active material of the positive electrode sheet is completed, a thin film of the positive electrode lithium supplement material is deposited on the surface of the positive electrode active material. After adding the positive electrode lithium supplement material, a lithium ion secondary battery is assembled, and during the first charging process, the delithiation of the positive electrode lithium supplement material can play the lithium supplement effect. It should be noted that the above "surface" can be the entire area of the positive electrode current collector / positive electrode active material or a partial area of the positive electrode current collector / positive electrode active material. The present application does not have a special limitation as long as the purpose of the present application can be achieved.

[0029] The negative electrode sheet of the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the negative electrode sheet generally includes a negative electrode current collector and a negative electrode active material layer. Among them, the negative electrode current collector is not particularly limited as long as the purpose of the present application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector, etc. The negative electrode active material layer includes a negative electrode active material, a conductive agent and a thickener. The negative electrode active material of the present application can include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 < x < 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12, at least one of Li-Al alloy, metallic lithium, etc. In this application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the object of this application can be achieved. For example, the thickness of the negative electrode current collector is 6 μm to 10 μm, and the thickness of the negative electrode active material layer is 30 μm to 120 μm. In this application, there is no particular limitation on the thickness of the negative electrode sheet, as long as the object of this application can be achieved. For example, the thickness of the negative electrode sheet is 50 μm to 150 μm. Optionally, the negative electrode sheet may further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode material layer. The composition of the conductive layer is not particularly limited and may be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder.

[0030] There is no particular limitation on the above-mentioned conductive agent, as long as the object of this application can be achieved. For example, the conductive agent may include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon nanofibers, flake graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, or graphene, etc. There is no particular limitation on the above-mentioned binder, and any binder well-known in the art may be used, as long as the object of this application can be achieved. For example, the binder may include at least one of polyvinyl alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyimide, polyamideimide, styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinylidene fluoride, polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), aqueous acrylic resin, carboxymethyl cellulose (CMC), or sodium carboxymethyl cellulose (CMC-Na), etc.

[0031] The separator membrane in this application is not particularly limited as long as it can achieve the purpose of this application. For example, at least one of polyolefin (PO) membranes mainly composed of polyethylene (PE) and polypropylene (PP), polyester membranes (such as polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide membranes (PI), polyamide membranes (PA), spandex or aramid membranes, woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, separator papers, rolled membranes, spun membranes, etc. For example, the separator membrane may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, membrane or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide, etc. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are not particularly limited. For example, they may be selected from at least one of alumina, silica, magnesia, 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 and barium sulfate, etc. The binder is not particularly limited. For example, it may be selected from one or a combination of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinyl pyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate salt, polyvinyl pyrrolidone, polyethylene ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene), etc.

[0032] The lithium-ion secondary battery of the present application further includes an electrolyte, which may be at least one of a gel electrolyte, a solid electrolyte, and an electrolytic solution. The electrolytic solution includes a lithium salt and a non-aqueous solvent. In some embodiments of the present application, the lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, or lithium difluoroborate. For example, LiPF6 may be selected as the lithium salt because it can provide high ionic conductivity and improve the cycling characteristics. The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof. The above carbonate compound may be a linear carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound, or a combination thereof. Examples of the above linear carbonate compounds are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VEC), and combinations thereof. Examples of the fluorinated carbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethyl ethylene carbonate, and combinations thereof. Examples of the above carboxylate compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, and combinations thereof. Examples of the above ether compounds are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof. Examples of the above other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters, and combinations thereof.

[0033] The fourth aspect of the present application provides an electrochemical device, including the positive electrode sheet provided by the present application, and this electrochemical device has good energy density. The electrochemical device of the present application is not particularly limited, and it can include any device that undergoes an electrochemical reaction. In some embodiments, the electrochemical device can include, but is not limited to: lithium metal secondary batteries, lithium ion secondary batteries (lithium ion batteries), lithium polymer secondary batteries, or lithium ion polymer secondary batteries, etc.

[0034] The present application also provides an electronic device, including the electrochemical device described in the embodiments of the present application, and this electronic device has good energy density. The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, laptop computers, pen input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal TVs, portable cleaners, portable CD players, minidiscs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium ion capacitors, etc.

[0035] The preparation process of the electrochemical device is well-known to those skilled in the art, and the present application has no special limitations. For example, the electrochemical device can be manufactured through the following process: overlapping the positive electrode sheet and the negative electrode sheet via a separator, and after winding, folding, etc. as required, placing them in a housing, injecting the electrolyte into the housing and sealing it, where the separator used is the above-mentioned separator provided by the present application. In addition, an overcurrent protection element, a guide plate, etc. can be placed in the housing as required to prevent the pressure inside the electrochemical device from rising and overcharging and discharging.

[0036] The present application provides a positive electrode lithium supplement material, a positive electrode sheet containing this material, and an electrochemical device. The positive electrode lithium supplement material includes: a matrix of xLi2O·yM, and carbon present on this matrix; where x > 0, 0.4x ≤ y ≤ 2x, and M includes at least one of Mn, Fe, Co, Ni, Cu, Cr, or V. This positive electrode lithium supplement material has strong chemical stability and can effectively improve the particle agglomeration phenomenon during the slurry mixing process. Applying this positive electrode lithium supplement material in the positive electrode sheet can achieve the supplement of active lithium and effectively improve the energy density of the electrochemical device. Brief Description of the Drawings

[0037] In order to more clearly illustrate the technical solutions of the present application and the prior art, the following briefly introduces the drawings required for use in the embodiments and the prior art. Obviously, the drawings in the following description are only some embodiments of the present application.

[0038] Figure 1 XRD (X-ray diffraction) pattern of the positive electrode lithium supplement material of Example 1 of the present application;

[0039] Figure 2 SEM (scanning electron microscope) image of the positive electrode lithium supplement material of Example 1 of the present application;

[0040] Figure 3 EDS (X-ray energy spectrum analysis) spectrum of cobalt element in the positive electrode lithium supplement material of Example 1 of the present application;

[0041] Figure 4 EDS spectrum of oxygen element in the positive electrode lithium supplement material of Example 1 of the present application;

[0042] Figure 5 EDS spectrum of carbon element in the positive electrode lithium supplement material of Example 1 of the present application. Detailed implementation manners

[0043] To make the objectives, technical solutions, and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other technical solutions obtained by those of ordinary skill in the art based on the embodiments in the present application fall within the scope of protection of the present application.

[0044] It should be noted that in the specific implementation manners of the present application, a lithium-ion secondary battery is taken as an example of the electrochemical device to explain the present application. However, the electrochemical device of the present application is not limited to lithium-ion secondary batteries.

[0045] Figure 1 The XRD pattern of the positive electrode lithium supplement material of Example 1 of the present application is shown. Among them, Figure 1 in (a) is the pattern of the positive electrode lithium supplement material, Figure 1 in (b) is the Co standard diffraction card, Figure 1 in (c) is the Li2O standard diffraction card. As Figure 1 shown, in the (a) pattern, it can be seen that diffraction peaks at 2θ of 44.2° and 51.5° appear, corresponding to the diffraction peaks of Co; diffraction peaks at 2θ of 33.1°, 38.4°, 55.4°, 66.0°, and 69.4° appear, corresponding to the diffraction peaks of Li2O, indicating that Co and Li2O exist in the positive electrode lithium supplement material of Example 1 of the present application.

[0046] Figure 2 The SEM image of the positive electrode lithium supplement material of Example 1 of the present application is shown. As Figure 2 shown, the particle size distribution of the positive electrode lithium supplement material is uniform.Figure 3 The EDS spectrum of cobalt element in the cathode lithium supplement material of Example 1 of the present application is shown, indicating that the cathode lithium supplement material of the present application contains cobalt element and is uniformly distributed in the cathode lithium supplement material. Figure 4 The EDS spectrum of oxygen element in the cathode lithium supplement material of Example 1 of the present application is shown, indicating that the cathode lithium supplement material of the present application contains oxygen element and is uniformly distributed in the cathode lithium supplement material. Figure 5 The EDS spectrum of carbon element in the cathode lithium supplement material of Example 1 of the present application is shown, indicating that the cathode lithium supplement material of the present application contains carbon element and is uniformly distributed in the cathode lithium supplement material.

[0047] Example

[0048] Hereinafter, examples and comparative examples are given to illustrate the embodiments of the present application more specifically. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0049] Testing methods and equipment:

[0050] First charge specific capacity test:

[0051] <Preparation of coin cell>

[0052] The cathode lithium supplement material to be tested, conductive agent conductive carbon black (Super P) and binder polyvinylidene fluoride (PVDF) are mixed according to a mass ratio of 80:10:10, N-methylpyrrolidone (NMP) is added as a solvent, and after stirring and blending, a slurry with a solid content of 40% is obtained. The slurry is coated on the current collector aluminum foil with a thickness of 100 μm by a doctor blade, and after drying in a vacuum drying oven at 130 °C for 12 h, it is cut into a disc with a diameter of 1 cm by a punching machine in a dry environment. In a glove box, a lithium metal sheet is used as the counter electrode, the separator membrane is selected as the ceglard composite membrane, and the electrolyte is added to assemble a coin cell. The electrolyte is an organic solution obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a mass ratio of 30:50:20, and then lithium salt lithium hexafluorophosphate is added to the organic solvent and dissolved and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0053] <Test of first charge specific capacity>

[0054] The present application uses the Wuhan Blue Electric CT2001A system to test the charge specific capacity. The coin cell to be tested containing the cathode lithium supplement material is left standing in an environment of 25 ± 3 °C for 30 min, and is charged at a constant current of 0.1C (the theoretical gram capacity of the cathode lithium supplement material is calculated as 600 mAh / g) until the voltage reaches 4.45 V, and then charged at a constant voltage until the current reaches 0.025C, and the first charge capacity is recorded.

[0055] The specific charge capacity of the coin cell with the positive electrode lithium supplement material = the first charge capacity / the mass of the positive electrode lithium supplement material.

[0056] First discharge capacity test:

[0057] Let the secondary lithium-ion battery to be tested containing the positive electrode lithium supplement material stand still in an environment of 25 ± 3 °C for 30 min, then charge it at a constant current of 600 mA (the rated capacity is calculated as 2000 mAh) until the voltage reaches 4.4 V, and then charge it at a constant voltage until the current reaches 50 mA. After standing still for 5 min, discharge it at a constant current of 600 mA until the cut-off voltage of 3.0 V, and record the first discharge capacity.

[0058] Example 1

[0059] <Preparation of the positive electrode lithium supplement material>

[0060] Disperse 128.17 g of naphthalene in 1 L of tetrahydrofuran solvent, slowly add 5.55 g of lithium metal fragments, and react evenly to obtain a lithium naphthalene solution; weigh 24.08 g of the oxide Co3O4, slowly add it to the above lithium naphthalene solution, stir and react evenly, then filter and dry to obtain a matrix of 4Li2O·3Co; ball-mill and mix 10 g of the above matrix of 4Li2O·3Co with 0.05 g of the inorganic carbon source carbon black, and disperse evenly to obtain a mixture; calcine the above mixture in an inert atmosphere at 600 °C for 8 h to obtain a positive electrode lithium supplement material with carbon existing on the matrix of 4Li2O·3Co. Based on the total mass of the positive electrode lithium supplement material, the mass percentage of carbon is 0.5%.

[0061] <Preparation of the positive electrode sheet>

[0062] Mix the positive electrode active material lithium cobalt oxide (LiCoO2), the positive electrode lithium supplement material prepared above, the conductive agent SuperP, and the binder PVDF according to a mass ratio of 95:2:1.5:1.5, add NMP as a solvent, and prepare a slurry with a solid content of 75%, and stir evenly. Coat the slurry evenly on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, and dry it at 130 °C to obtain a positive electrode sheet with a coating thickness of 110 μm. After the above steps are completed, the single-sided coating of the positive electrode sheet is completed. Then, repeat the above steps on the other surface of the positive electrode sheet to obtain a positive electrode sheet with the positive electrode active material double-sided coated. After coating, cut the positive electrode sheet into a specification of 74 mm × 867 mm and weld the tab for use.

[0063] <Preparation of the negative electrode sheet>

[0064] Graphite, negative electrode active material SiO, conductive agent carbon black nanofiber, and binder polyvinyl alcohol (PAA) were mixed in a mass ratio of 78:15:3:4. Deionized water was added as a solvent to prepare a slurry with a solid content of 60%, and the slurry was stirred evenly. Then, an appropriate amount of deionized water was added to adjust the viscosity of the slurry to 5000 Pa·s, and a negative electrode slurry was prepared. The slurry was evenly coated on a negative electrode current collector copper foil with a thickness of 8 μm and dried at 110 °C. After cold pressing, a negative electrode plate with a single-sided coated active material layer with an active material layer thickness of 100 μm was obtained. After the above steps were completed, these steps were also completed on the back of the negative electrode plate in the same manner, that is, a negative electrode plate with double-sided coating was obtained. After coating, the negative electrode plate was cut into a size of 76 mm × 851 mm and the tab was welded for use.

[0065] <Preparation of electrolyte>

[0066] In a dry argon atmosphere, organic solvents EC, EMC, and DEC were mixed in a mass ratio of 30:50:20 to obtain an organic solution. Then, lithium salt lithium hexafluorophosphate was added to the organic solvent and dissolved and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0067] <Preparation of separator>

[0068] A polypropylene (PP) film with a thickness of 14 μm (provided by Celgard) was used.

[0069] <Preparation of lithium ion secondary battery>

[0070] The positive electrode, separator, and negative electrode prepared above were stacked in sequence, and the separator was placed in the middle of the positive and negative electrodes to play a role in isolation, and then wound to obtain an electrode assembly. The electrode assembly was placed in an aluminum-plastic film packaging bag, dehydrated at 80 °C, injected with the prepared electrolyte, and then subjected to processes such as vacuum packaging, standing, forming, and shaping to obtain a lithium ion secondary battery.

[0071] In Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, Example 10, Example 11, Example 12, Example 13, Example 14, Example 15, and Example 16, the preparation steps of <Preparation of positive electrode lithium supplement material>, <Preparation of positive electrode plate>, <Preparation of negative electrode plate>, <Preparation of electrolyte>, <Preparation of separator>, and <Preparation of lithium ion secondary battery> were the same as those in Example 1, and the changes in relevant preparation parameters are shown in Table 1:

[0072] Table 1

[0073]

[0074] Example 17

[0075] <Preparation of negative electrode sheet>

[0076] Mix the negative electrode active material graphite, nano-conductive carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose in a mass ratio of 95:2:2:1, add deionized water as a solvent, and formulate into a slurry with a solid content of 70%, and stir evenly. Coat the slurry evenly on the negative electrode current collector copper foil with a thickness of 8 μm, dry it at 110 °C, and obtain a negative electrode sheet with a single-sided coated active material layer with an active material layer thickness of 150 μm after cold pressing. After the above steps are completed, these steps are also completed on the back of the negative electrode sheet in the same way, that is, a double-sided coated negative electrode sheet is obtained. After coating is completed, cut the negative electrode sheet into a specification of 76 mm × 851 mm and weld the tab for use.

[0077] The preparation of the positive electrode lithium supplement material, the preparation of the positive electrode sheet, the preparation of the electrolyte, the preparation of the separator, and the preparation of the lithium-ion secondary battery are the same as those in Example 1.

[0078] In Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4, the preparation steps of the positive electrode sheet, the negative electrode sheet, the electrolyte, the separator, and the lithium-ion secondary battery are all the same as those in Example 1. In Comparative Example 2, Comparative Example 3 and Comparative Example 4, the preparation of the positive electrode lithium supplement material is the same as that in Example 1, and the changes in relevant preparation parameters are shown in Table 2:

[0079] Table 2

[0080]

[0081] Note: " / " in Table 2 indicates that the corresponding preparation parameter does not exist.

[0082] Comparative Example 5

[0083] <Preparation of positive electrode lithium supplement material>

[0084] Mix metal lithium fragments and oxide Co3O4 in a molar ratio of 8:1 to obtain a first mixture; sinter the first mixture at 180 °C for 4 h under an argon protection atmosphere to obtain a second mixture; mix the second mixture with a mixed gas with a volume ratio of Ar, O2 and HF = 3:0.05:96.95 and react to obtain the positive electrode lithium supplement material 2.1Li2O·Co·0.5CoO 0.05 F 0.1 。

[0085] The preparation of the positive electrode sheet, the negative electrode sheet, the electrolyte, the separator, and the lithium-ion secondary battery is the same as that in Example 1.

[0086] The preparation parameters of Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, Example 10, Example 11, Example 12, Example 13, Example 14, Example 15, Example 16, Example 17, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Comparative Example 5 are shown in Table 3:

[0087]

[0088]

[0089] It can be seen from Example 1, Example 6, Example 7, Example 8, Example 9, Example 10, Example 11, Example 12, Comparative Example 1, and Comparative Example 5 that the present application uses inorganic carbon sources with the same composition and content to coat substrates with different compositions to form different cathode lithium supplement materials. Although the substrate compositions are different, as long as the substrate composition is within the scope of the present application, the chemical stability of the cathode lithium supplement material can be effectively improved, and the particle agglomeration phenomenon during the slurry mixing process of the cathode slurry can be effectively inhibited. Moreover, when the above cathode lithium supplement materials are applied to the cathode electrode sheet, the effective supplement of active lithium can be realized, and the energy density of the lithium-ion secondary battery can be effectively improved.

[0090] It can be seen from Example 1, Example 2, Example 3, Comparative Example 2, and Comparative Example 3 that the cathode lithium supplement material with the carbon content of the present application can effectively improve the first charge specific capacity of the cathode lithium supplement material, can realize the effective supplement of active lithium, and can effectively improve the energy density of the lithium-ion secondary battery.

[0091] The calcination temperature, calcination time of the cathode lithium supplement material, and the type of inorganic carbon source usually also affect the first charge specific capacity of the cathode lithium supplement material. It can be seen from Example 1, Example 4, and Example 5 that as long as the above preparation parameters are within the scope of the present application, the first charge specific capacity of the cathode lithium supplement material and the energy density of the lithium-ion secondary battery can be effectively improved.

[0092] It can be seen from Example 1, Example 13, Example 14, Example 15, Example 16, and Comparative Example 4 that when the content of the cathode lithium supplement material is within the scope of the present application, the first charge specific capacity of the cathode lithium supplement material and the energy density of the lithium-ion secondary battery can be effectively improved. Especially when the mass percentage content of the cathode lithium supplement material is preferably 3% to 10%, for example, Example 13, Example 14, Example 15, and Example 16, the energy density of the lithium-ion secondary battery can be more effectively improved.

[0093] Based on the above analysis, it can be seen that the positive electrode lithium supplement material provided by this application includes a matrix of xLi2O·yM and carbon existing on the matrix. The chemical stability of this positive electrode lithium supplement material is strong, and it can effectively improve the phenomenon of particle agglomeration during the slurry mixing process. Applying this positive electrode lithium supplement material to an electrochemical device can effectively supplement active lithium and effectively improve the energy density of the electrochemical device.

[0094] The above are only the preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application shall be included within the scope of protection of this application.

Claims

1. A positive electrode sheet, the positive electrode sheet comprising a positive electrode active material layer, the positive electrode active material layer comprising a positive electrode lithium supplement material, wherein the positive electrode lithium supplement material consists of a matrix of xLi2O·yM and carbon present on the matrix; Among them, x > 0, 0.4x ≤ y ≤ 2x, M comprises at least one of Mn, Fe, Co, Ni, Cu, Cr or V; based on the total mass of the positive electrode lithium supplement material, the mass percentage of the carbon is 0.5% to 3%, and based on the total mass of the positive electrode active material layer, the mass percentage of the positive electrode lithium supplement material is 1% to 3%; and wherein, the positive electrode lithium supplement material is prepared by a method comprising the following steps: (1) Disperse naphthalene in a solvent, slowly add lithium metal fragments or powder, and react uniformly to obtain a naphthalene lithium solution; (2) Slowly add oxide M a O b to the above-mentioned lithium naphthalide solution. After stirring the reaction evenly, filter and dry to obtain the matrix of xLi2O·yM; (3) Ball-mill and mix the matrix with an inorganic carbon source, and disperse uniformly to obtain a mixture; (4) Calcinate the mixture in an inert atmosphere to obtain the positive electrode lithium supplement material; Among them, the molar ratio of the naphthalene to the lithium metal is 1:(0.6 to 1), and the molar ratio of the naphthalene to the oxide M a O b is 1:(0.1 to 0.5), and the ratio of the number of moles of the naphthalene to the mass of the inorganic carbon source is 1:(0.05 to 0.3) mol / g.

2. The positive electrode sheet according to claim 1, wherein, the M comprises at least one of Mn, Fe, Co or Ni; the valence state of the M is 0 valence.

3. The positive electrode sheet according to claim 1, wherein, The first charge specific capacity of the positive electrode lithium supplement material ≥ 450 mAh / g.

4. The positive electrode plate according to claim 1, wherein, The solvent comprises at least one of tetrahydrofuran or ethylene glycol dimethyl ether; The oxide M a O b comprises at least one of MnO, Mn2O3, MnO2, FeO, Fe2O3, CoO, Co2O3, Co3O4, NiO, Ni2O3, Cu2O, CuO, CrO, Cr2O3, CrO3, VO, V2O3, VO2 or V2O5; The inorganic carbon source comprises at least one of carbon black, carbon gel, Ketjen black, acetylene black, carbon nanotubes or graphene; In step (4), the calcination temperature is 600 °C to 700 °C, and the calcination time is 4 h to 8 h.

5. An electrochemical device, which comprises the positive electrode sheet according to any one of claims 1 to 4.

6. An electronic device, which comprises the electrochemical device according to claim 5.

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