Positive active material, positive pole piece, cylindrical battery monomer, battery and electric device

Abstract

The invention relates to a positive electrode active material, a positive electrode plate, a cylindrical battery monomer, a battery and a power utilization device, the positive electrode active material comprises a core part and a coating layer, the core part comprises a lithium-containing transition metal oxide, the coating layer coats at least part of the surface of the core part, the coating layer comprises a polymer, and the polymer is a polymer. The polymer comprises one or more of a fluorine-containing polymer and an oxygen-containing polymer. When the positive electrode active material is applied to the battery, the expansion degree of the battery can be reduced, and the cycle performance of the battery can be improved.

Description

Positive electrode active material, positive electrode sheet, cylindrical battery cell, battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application 202410486790.2, filed on April 22, 2024, entitled "Positive electrode active material, positive electrode sheet, cylindrical battery cell, battery and power device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to a positive electrode active material, a positive electrode sheet, a cylindrical battery cell, a battery, and an electrical device. Background Technology

[0004] Batteries have high capacity and other characteristics, so they are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric airplanes, electric boats, electric toy cars, electric toy boats, electric toy airplanes and power tools, etc.

[0005] A battery includes a positive electrode. During charging, the positive electrode expands continuously, resulting in a high degree of battery expansion and potentially deteriorating the battery's cycle performance. Summary of the Invention

[0006] This application provides a positive electrode active material, a positive electrode sheet, a cylindrical battery cell, a battery, and an electrical device. In the embodiments of this application, when the positive electrode active material is applied to the battery, it can reduce the degree of battery expansion and improve the battery's cycle performance.

[0007] In a first aspect, embodiments of this application provide a positive electrode active material, which includes a core and a coating layer. The core includes a lithium-containing transition metal oxide, and the coating layer covers at least a portion of the surface of the core. The coating layer includes a polymer, which includes one or more of fluoropolymers and oxygen-containing polymers.

[0008] Therefore, the theoretical specific capacity of the lithium transition metal oxide in this embodiment is relatively high, which can effectively improve the energy density of the battery. A coating layer is provided on the surface of the core. The coating layer can cover part or all of the surface of the core. The coating layer includes a polymer, which can include one or more of fluoropolymers and oxygen-containing polymers. The polymer can effectively connect the positive electrode active material and the additives such as binders in the positive electrode sheet, so that the additives can change synchronously with the volume change of the positive electrode active material, especially when the positive electrode active material shrinks, thereby effectively reducing the overall volume expansion of the positive electrode sheet, reducing the full charge expansion of the battery cell, and improving the cycle performance of the battery cell.

[0009] In some embodiments, the fluoropolymer includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, and a terpolymer of tetrafluoroethylene-hexafluoropropylene.

[0010] The aforementioned fluoropolymer has strong adhesion to the positive electrode active material, and can effectively bond with the binders in the positive electrode film, thereby enhancing the bonding force between the parts and forming synchronous contraction and expansion. This makes it easier for the additives in the positive electrode film to change synchronously with the volume change of the positive electrode active material.

[0011] In some embodiments, the oxygen-containing polymer includes one or more of ether polymers and ester polymers.

[0012] The aforementioned oxygen-containing polymers possess excellent flexibility, which enhances the flexibility and ductility of the positive electrode film. Furthermore, they can react with the binder in the positive electrode film to reduce crystallinity, allowing the entire positive electrode film to deform in accordance with the volume changes of the positive electrode active material, thereby reducing expansion caused by volume changes and interfacial contact problems between components.

[0013] In some embodiments, the ether polymer includes one or more of polyethylene glycol and polypropylene glycol.

[0014] In some embodiments, the ester polymer includes one or more of polyvinyl acetate and polymethyl methacrylate.

[0015] In some embodiments, the polymer content in the positive electrode active material is 0.15% to 1.0% by mass. When the polymer content is within the above range, the core can be effectively coated, allowing the positive electrode active material and binder to shrink and expand at the same frequency, reducing the overall expansion rate of the positive electrode film, reducing the expansion degree of the battery cell, and improving the cycle performance of the battery cell.

[0016] In some embodiments, the polymer content in the positive electrode active material is 0.15% to 0.7% by mass. When the polymer content is within the above range, the overall expansion rate of the positive electrode film can be further reduced, the expansion degree of the battery cell can be reduced, and the cycle performance of the battery cell can be improved.

[0017] In some embodiments, the coating layer also includes a fast ion conductor. Fast ion conductors facilitate the rapid movement of active ions, such as lithium ions, enhancing their migration ability and allowing them to quickly extract from the cathode active material. This reduces micro-stress within the particles caused by uneven intercalation and deintercalation of active ions, decreases anisotropy, and thus reduces the risk of volume expansion in the cathode active material.

[0018] In some embodiments, the fast ion conductor in the positive electrode active material has a mass content of 0.5% to 2.5%. A mass content of fast ion conductor within this range further enables the rapid extraction of active ions from the positive electrode active material, reducing micro-stress caused by uneven intercalation and deintercalation of active ions within the particles, reducing anisotropy, and thus reducing the risk of volume expansion of the positive electrode active material.

[0019] In some embodiments, the fast ion conductor in the positive electrode active material is present in a mass content of 0.5% to 2.0%. Having a fast ion conductor within this range further reduces the risk of volume expansion of the positive electrode active material.

[0020] In some embodiments, the coating layer includes a first layer and a second layer. The first layer covers the surface of the core and includes a fast ion conductor. The second layer is disposed on the side of the first layer away from the core and includes a polymer. The polymer is located in the outer layer and can effectively connect the positive electrode active material and the additives in the positive electrode film layer. The fast ion conductor is located in the layer closer to the core, which is more conducive to guiding active ions to quickly escape from the core and reducing the risk of volume expansion of the positive electrode active material.

[0021] In some embodiments, lithium-containing transition metal oxides include those with the general formula Li x A y Ni a Co b Mn c M (1-a-b-c) Q z The compounds contain the following properties: 0 < x ≤ 2.1, 0 ≤ y ≤ 2.1, and 0.9 ≤ x + y ≤ 2.1; 0 < a < 1, 0 < b < 1, 0 ≤ c < 1, and 0.1 ≤ a + b + c ≤ 1; 1.8 ≤ z ≤ 3.5; A includes one or more of Na, K, and Mg; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, and Se; Q includes one or more of O and F. The theoretical specific capacity of the above lithium-containing transition metal oxides is relatively high, which is beneficial for improving the energy density of battery cells.

[0022] In some implementations, 0.6 ≤ a ≤ 1. The theoretical specific capacity of the aforementioned lithium-containing transition metal oxides is relatively high, which is beneficial for improving the energy density of individual battery cells.

[0023] In some embodiments, the volume average particle size D of the positive electrode active material v50 is 5μm to 15μm. When the volume average particle size of the positive electrode active material is within the above range, the active surface of the positive electrode active material is relatively large, and its contact area with other additives in the positive electrode film is large. The polymer on the surface of the positive electrode active material can improve the adhesion between the positive electrode active material and additives, and reduce the volume expansion of the positive electrode sheet.

[0024] In some embodiments, the volume average particle size D of the positive electrode active material v 50 is 7μm to 12μm. When the volume average particle size of the positive electrode active material is within the above range, the polymer on the surface of the positive electrode active material can improve the adhesion between the positive electrode active material and additives, and further reduce the volume expansion of the positive electrode sheet.

[0025] Secondly, embodiments of this application also propose a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector, the positive electrode film layer including a positive active material as described in any embodiment of the first aspect of this application.

[0026] In some embodiments, the positive electrode film layer further includes a positive electrode binder, which includes one or more of fluoropolymers and acrylate resins. The aforementioned positive electrode binder can effectively cooperate with the polymer in the positive electrode active material, improving the connection between the positive electrode active material and the positive electrode binder, achieving synchronous volume changes between the positive electrode active material and the positive electrode binder, and reducing the degree of expansion of the positive electrode sheet.

[0027] In some embodiments, the fluorinated polymer includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, and a copolymer of tetrafluoroethylene-hexafluoropropylene; and / or

[0028] In some embodiments, the acrylate resin includes one or more of polymethyl fluorinated acrylate and polyacrylate.

[0029] Thirdly, embodiments of this application also propose a cylindrical battery cell, which includes a positive electrode as described in any embodiment of the second aspect of this application.

[0030] In some implementations, the full-charge expansion rate of the positive electrode is less than or equal to 6%. The relatively small expansion rate of the positive electrode is beneficial for reducing the overall expansion rate of the battery cell.

[0031] In some implementations, the full-charge expansion rate of the positive electrode is less than or equal to 4.9%. The relatively small expansion rate of the positive electrode is beneficial for reducing the overall expansion rate of the battery cell.

[0032] In some embodiments, the cylindrical battery cell includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. The negative electrode active material is a silicon-based material, and based on the mass of the negative electrode active material, the mass content of silicon in the silicon-based material in the negative electrode film layer is between 1% and 50%. When the mass content of silicon is within the above range, the theoretical specific capacity of the negative electrode active material is relatively high, which can effectively improve the energy density of the battery cell.

[0033] In some embodiments, the cylindrical battery cell further includes a housing, the housing comprising a casing and an end cap, the casing having an opening and the end cap closing the opening; the casing includes an integrally formed sidewall and an end wall, the end wall and the end cap being axially opposed along the cylindrical battery cell, the end cap being connected to the sidewall.

[0034] In some embodiments, the cylindrical battery cell further includes electrode terminals, which are insulated from the end wall; the positive electrode includes a positive electrode tab, which is electrically connected to the electrode terminal; the cylindrical battery cell includes a negative electrode, which includes a negative electrode tab, which is electrically connected to the end cap.

[0035] In some embodiments, the cylindrical battery cell further includes a housing, the dimension of which along the axial direction of the cylindrical battery cell is 1.3 to 2.5 times the dimension of which along the radial direction of the cylindrical battery cell is.

[0036] In some embodiments, the housing has a dimension of 50 mm to 150 mm along the axial direction.

[0037] In some embodiments, the outer casing has a radial dimension of 40 mm to 80 mm.

[0038] Fourthly, this application also proposes a battery, which includes a cylindrical battery cell according to any embodiment of the third aspect of this application.

[0039] Fifthly, embodiments of this application also propose an electrical device including a battery as described in any embodiment of the fourth aspect of this application. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0041] Figure 1 is a schematic diagram of one embodiment of the battery cell of this application.

[0042] Figure 2 is an exploded view of the embodiment of the battery cell in Figure 1.

[0043] Figure 3 is a schematic diagram of one embodiment of the battery module of this application.

[0044] Figure 4 is a schematic diagram of one embodiment of the battery of this application.

[0045] Figure 5 is a schematic diagram of one embodiment of an electrical device that uses the battery cell of this application as a power source.

[0046] The accompanying drawings may not be drawn to scale.

[0047] The reference numerals in the attached drawings are explained as follows: 1. Electrical device; 2. Battery; 3. Controller; 4. Motor; 5. Housing; 5a. First housing section; 5b. Second housing section; 5c. Receiving space; 6. Battery module; 7. Battery cell; 10. Electrode assembly; 111. First electrode tab; 112. Second electrode tab; 12. Main body section; 20. Outer shell; 21. Housing; 211. End wall; 212. Side wall; 22. End cap; 30. Electrode terminal; 40. Current collector. Detailed Implementation

[0048] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, positive electrode sheet, cylindrical battery cell, battery, and power device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0049] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0050] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0051] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0052] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0053] A battery cell includes an electrode assembly, which can be cylindrical, flat, or other shapes. When the electrode assembly is cylindrical, the battery cell is a cylindrical battery cell. When the electrode assembly is flat, the battery cell is a prismatic battery cell.

[0054] The electrode assembly in a cylindrical battery cell is usually a wound structure. The remaining space in the wound structure is small. During the charging process of the battery cell, the positive electrode active material in the positive electrode sheet contained in the electrode assembly may expand. Specifically, in the early stage of charging, a large number of active ions are released from the positive electrode active material. The migration of a large number of ions with the same charge will lead to an increase in repulsion, and the degree of expansion inside the positive electrode active material will increase. In the later stage of charging, the number of active ions released from the positive electrode active material decreases, the repulsion between ions with the same charge decreases, and the positive electrode active material tends to shrink.

[0055] In the early stages of charging, the significant expansion of the positive electrode active material causes additives such as binders attached to its surface to shift position along with the expansion. In the later stages of charging, the positive electrode active material shrinks, but the binder, with its limited deformation capacity, may not shift position due to this shrinkage. During the next charge cycle, the positive electrode active material expands further, causing the binder to continue shifting position, resulting in further expansion of the positive electrode sheet. This expansion increases with the number of charging cycles, leading to increased overall expansion of the battery cell and negatively impacting its reliability.

[0056] In addition, the volume expansion of the positive electrode sheet increases the compressive force between the electrodes, causing wrinkles and damage to the positive electrode sheet, which may lead to a decrease in the cycle performance of the battery cell.

[0057] In view of the above problems, this application proposes a positive electrode active material, which includes a core mainly composed of lithium transition metal oxide, and a polymer disposed on the surface of the core. The polymer can effectively connect the positive electrode active material and the additives in the positive electrode sheet, so that the additives can change synchronously with the volume change of the positive electrode active material, thereby effectively reducing the volume expansion of the positive electrode sheet, reducing the expansion degree of the battery cell, and improving the cycle performance of the battery cell. The positive electrode active material will be described in detail below.

[0058] Positive electrode active material

[0059] This application proposes a positive electrode active material.

[0060] The positive electrode active material includes a core and a coating layer. The core includes a lithium-containing transition metal oxide, and the coating layer covers at least a portion of the surface of the core. The coating layer includes a polymer, which includes one or more of fluoropolymers and oxygen-containing polymers.

[0061] Lithium-containing transition metal oxides have a relatively high theoretical specific capacity, which can effectively improve the energy density of the battery. A coating layer is provided on the surface of the core. The coating layer can cover part or all of the surface of the core. The coating layer includes a polymer, which can include one or more of fluoropolymers and oxygen-containing polymers. The polymer can effectively connect the positive electrode active material and the additives such as binders in the positive electrode sheet, so that the additives can change synchronously with the volume change of the positive electrode active material, especially when the positive electrode active material shrinks. This effectively reduces the overall volume expansion of the positive electrode sheet, reduces the full charge expansion of the battery cell, and improves the cycle performance of the battery cell.

[0062] Polymers include various types. For example, polymers with strong adhesion to the positive electrode active material can effectively bond with binders in the positive electrode film, enhancing the bonding force between different parts and forming synchronous contraction and expansion, making the additives in the positive electrode film more likely to change synchronously with the volume change of the positive electrode active material. In some embodiments, the polymer may include fluoropolymers; exemplaryly, fluoropolymers include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTEE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer; optionally, fluoropolymers include one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTEE).

[0063] For example, the polymer's excellent flexibility enhances the flexibility and ductility of the positive electrode film. Furthermore, it can react with binders in the positive electrode film, such as polyvinylidene fluoride (PVDF), to reduce crystallinity. This allows the entire positive electrode film to deform in response to volume changes in the positive electrode active material, reducing expansion caused by volume changes and minimizing interfacial contact problems between components. In some embodiments, the polymer may include an oxygen-containing polymer.

[0064] For example, oxygen-containing polymers may include one or more of ether polymers and ester polymers.

[0065] For example, ether polymers include one or more of polyethylene glycol and polypropylene glycol. Ether polymers have good flexibility and can reduce the crystallinity of binders such as polyvinylidene fluoride (PVDF) in the positive electrode film by disrupting hydrogen bonds and CF bonds in the binder, making it easier for the positive electrode active material and binder to shrink and expand at the same frequency.

[0066] For example, ester polymers include one or more of polyvinyl acetate and polymethyl methacrylate. Ester polymers have good flexibility and can undergo hydrogen bond recombination during the preparation of the positive electrode slurry, enabling them to crosslink with binders such as polyvinylidene fluoride (PVDF) in the positive electrode film layer. This improves the connection between the positive electrode active material and the binder, allowing the positive electrode active material and the binder to shrink and expand at the same frequency.

[0067] In some embodiments, the polymer content in the positive electrode active material is 0.15% to 1% by mass, optionally 0.15% to 0.7%, such as 0.15%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any combination of two of the above values.

[0068] When the polymer mass content is within the above range, it can effectively coat the core, enabling the positive electrode active material and binder to shrink and expand at the same frequency, reducing the overall expansion rate of the positive electrode film, reducing the expansion degree of the battery cell, and improving the cycle performance of the battery cell.

[0069] In some embodiments, the coating layer may also include a fast ion conductor. Fast ion conductors facilitate the rapid movement of active ions, such as lithium ions, enhancing their migration ability and allowing them to quickly extract from the cathode active material. This reduces micro-stress within the particles caused by uneven intercalation and deintercalation of active ions, decreases anisotropy, and thus reduces the risk of volume expansion in the cathode active material.

[0070] For example, fast ion conductors include one or more of lithium titanate, lithium aluminate, lithium cobalt oxide, lithium tungstate, lithium cerium oxide, lithium phosphate, lithium vanadium phosphate, lithium borate, lithium strontium oxide, lithium yttrium oxide, lithium lanthanum zirconate, lithium lanthanum titanate, and aluminum fluoride.

[0071] For example, fast ion conductors include one or more of lithium titanate, lithium aluminate, lithium cobalt oxide, lithium tungstate, lithium cerium oxide, lithium phosphate, lithium vanadium phosphate, lithium borate, lithium strontium oxide, lithium yttrium oxide, lithium lanthanum zirconate, lithium lanthanum titanate, and aluminum fluoride.

[0072] In some embodiments, the fast ion conductor has a mass content of 0.5% to 2.5% in the positive electrode active material, optionally from 0.5% to 2.0%, such as 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, or any range of two of the above values.

[0073] When the mass content of fast ion conductors is within the above range, it can further enable the active ions in the positive electrode active material to be rapidly extracted, reduce the micro-stress caused by the uneven intercalation and deintercalation of active ions inside the particles, reduce anisotropy, and thus reduce the risk of volume expansion of the positive electrode active material.

[0074] The coating layer can be a single-layer structure or a multi-layer composite structure. In the case of a single-layer coating layer, the fast-ion conductor and the polymer can reside in the same coating layer. In the case of a multi-layer composite coating layer, the fast-ion conductor and the polymer can reside in different layers; for example, the polymer can be located in a layer closer to the core, and the fast-ion conductor in a layer away from the core; or, for example, the fast-ion conductor can be located in a layer closer to the core, and the polymer in a layer away from the core.

[0075] For example, the coating layer may include a first layer and a second layer, the first layer covering the surface of the core and including a fast ion conductor; the second layer is disposed on the side of the first layer away from the core and includes a polymer.

[0076] The polymer is located in the outer layer, which can effectively connect the positive electrode active material and the additives in the positive electrode film layer; the fast ion conductor is located in the layer near the core, which is more conducive to guiding the active ions to quickly escape from the core and reducing the risk of volume expansion of the positive electrode active material.

[0077] In the embodiments of this application, the microstructure and material of the coating layer are known in the art and can be prepared using equipment and methods known in the art. According to JY / T 010-1996 "General Rules for Analytical Scanning Electron Microscopy" and GB / T17359-2012 "Quantitative Analysis by Microbeam Analysis and Energy Dispersive Spectroscopy", the analysis and testing are performed using scanning electron microscopy (SEM), argon ion polishing (CP), and energy dispersive spectroscopy (EDS).

[0078] In the embodiments of this application, the functional groups of the polymer have the meanings known in the art and can be determined using commonly used equipment and methods in the art. Infrared spectrophotometry (IR) can be used for detection. Specifically, the polymer is tested using a Thermo Nicolet Nexus 670 attenuated total reflectance Fourier transform infrared spectrometer (FTIR-ATR), and then tested according to standard GB / T6040-2002. The test range is 600–4000 cm⁻¹ using the ATR method. -1 Repeatability: ±2cm -1 Resolution: Better than 4cm -1 ; Transmission depth 0.2~0.6μm.

[0079] In the embodiments of this application, the structure of the polymer is known in the art and can be determined using commonly used equipment and methods in the art. Nuclear magnetic resonance (NMR) testing can be used. Specifically, 1H NMR and 13C NMR are performed on a Varian Mercury Plus-400 NMR spectrometer at a test temperature of 20°C, with TMS as an internal standard, CDCl3 as a solvent, and a proton resonance frequency of 400MHz.

[0080] In some embodiments, lithium-containing transition metal oxides include those with the general formula Li x A y Ni a Co b Mn c M (1-a-b-c) Q z Compounds wherein 0 < x ≤ 2.1, 0 ≤ y ≤ 2.1, and 0.9 ≤ x + y ≤ 2.1; 0 < a < 1, 0 < b < 1, 0 ≤ c < 1, and 0.1 ≤ a + b + c ≤ 1; 1.8 ≤ z ≤ 3.5; A includes one or more of Na, K, and Mg; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, and Se; Q includes one or more of O and F.

[0081] Optionally, 0.6 ≤ a < 1; further optionally, 0.8 ≤ a < 1; further optionally, 0.8 ≤ a ≤ 0.95. The theoretical specific capacity of the above-mentioned lithium-containing transition metal oxides is relatively high, which is beneficial to improving the energy density of battery cells.

[0082] a can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, or a range consisting of any two of the above values.

[0083] 0 < b < 1. b can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, or a range consisting of any two of the above values.

[0084] 0 < c < 1. c can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, or a range consisting of any two of the above values.

[0085] Specifically, lithium-containing transition metal oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 02 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1O2(NCM811), LiNi 0.80 Co 0.15 Al 0.05 One or more of O2.

[0086] During the charge and discharge process, battery cells are accompanied by the deintercalation and deintercalation of active ions, such as Li, and their molar content varies when the battery cells are discharged to different states. The molar content of Li in the examples of positive electrode active materials in the embodiments of this application refers to the material's initial state, i.e., the state before the materials are added. When the positive electrode active material is used in a battery system, the molar content of Li may change after charge and discharge cycles.

[0087] In the embodiments of this application, the molar content of oxygen (O) in the positive electrode active materials is only a theoretical value. Oxygen release from the crystal lattice will cause the molar content of oxygen (O) to change. In reality, the molar content of oxygen (O) will fluctuate.

[0088] In some embodiments, the positive electrode active material is in particulate form, with a volume average particle size D. v 50 is 5μm to 15μm, and can be selected from 7μm to 12μm, for example 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm or any range of two of the above values.

[0089] The positive electrode active material includes polymers. Polymers can effectively connect positive electrode active materials and binders with different particle sizes. When the volume average particle size of the positive electrode active material is within the above range, the active surface of the positive electrode active material is relatively large, and its contact area with other additives in the positive electrode film layer is large. The polymer on the surface of the positive electrode active material can improve the bonding performance between the positive electrode active material and additives, and reduce the volume expansion of the positive electrode sheet.

[0090] In the embodiments of this application, the volume average particle size D v50 refers to the particle size corresponding to 50% of the volume distribution. This can be detected using equipment and methods known in the art. Freshly prepared positive electrode active material can be used as a sample, or a fresh battery cell can be fully charged to 0% SOC, the positive electrode sheet can be removed, the positive current collector removed, and the positive electrode film layer retained. The positive electrode film layer is then immersed in N-methylpyrrolidone (NMP) to wash away the binder, leaving the positive electrode active material. After drying, the positive electrode active material is tested according to the testing standard GB / T 19077-2016 using a Mastersizer 3000 laser particle size analyzer to determine the volume average particle size (Dv50). In the embodiments of this application, a fresh battery cell can be a battery cell that has just left the factory (not yet charged / discharge cycled after formation) or a battery cell assembled in an electrical device and used for less than 10 cycles.

[0091] In this application embodiment, the positive electrode active material can be prepared by the following steps, the preparation method including:

[0092] Step 100: Provide a lithium-containing transition metal oxide;

[0093] Step 200: A coating layer is formed on the surface of a lithium transition metal oxide, the coating layer comprising a polymer.

[0094] In some implementations, step 200 may include:

[0095] Step 210: The lithium-containing transition metal oxide and the polymer are mixed and then heat-treated to melt the polymer and coat the surface of the lithium-containing transition metal oxide. After cooling, a coating layer is formed.

[0096] It should be noted that the heat treatment temperature is above the polymer's melting temperature, causing the polymer to change from a solid state to a fluid state, thus enabling it to more fully coat the surface of the lithium-containing transition metal oxide.

[0097] The heat treatment temperature is lower than the carbonization temperature of the polymer, so the polymer basically only undergoes a physical state change and basically does not undergo a chemical reaction.

[0098] In some embodiments, the polymer may include one or more of fluoropolymers and oxygen-containing polymers.

[0099] For example, the heat treatment temperature can be from 200°C to 600°C, and optionally from 300°C to 550°C.

[0100] For example, the heat treatment time can be 3 hours to 10 hours, and optionally 5 hours to 8 hours.

[0101] For example, the heating rate of the heat treatment can be from 0.5°C / min to 5°C / min, and can be selected from 1°C / min to 3°C / min.

[0102] For example, the atmosphere for heat treatment is at least one protective gas selected from nitrogen, argon, etc.

[0103] In some embodiments, in step 200, the coating layer further includes a fast ion conductor.

[0104] For example, step 200 may include:

[0105] Step 220: After mixing the lithium-containing transition metal oxide and the fast ion conductor source and heat-treating them, the fast ion conductor source can form a fast ion conductor layer. The fast ion conductor layer coats the surface of the lithium-containing transition metal oxide to obtain intermediate particles.

[0106] Step 210: After mixing the intermediate particles and the polymer, heat treatment is performed to melt the polymer and coat the surface of the lithium transition metal oxide. After cooling, the polymer and the fast ion conductor layer form a coating layer.

[0107] For example, in step 220, the fast ion conductor source may include at least one of oxides, hydroxides, carbonates, phosphates, fluorides, etc.

[0108] For example, in step 220, the processing conditions for the lithium-containing transition metal oxide and fast ion conductor source are a heat treatment temperature of 500°C to 700°C and a heat treatment time of 3h to 10h.

[0109] Step 100: The lithium-containing transition metal oxide can be prepared according to methods and equipment known in the art, such as co-precipitation, solid-phase method, etc.

[0110] In some implementations, step 100 may include:

[0111] Step 110: Prepare a mixed salt solution A of nickel, cobalt, and manganese salts at a certain concentration. The molar ratio of Ni:Co:Mn in mixed salt solution A is a:b:c, where 0 < a < 1, 0 < b < 1, and 0 ≤ c < 1. Prepare precipitant solution B and complexing agent solution C. Pump mixed solution A, precipitant solution B, and complexing agent solution C into a reaction vessel. Control the pH and reaction temperature of the materials in the reaction vessel to carry out a co-precipitation reaction. After the material particles in the vessel grow to the target particle size, the ternary material precursor is obtained after the reaction is completed.

[0112] Step 120: The ternary material precursor synthesized in step 110 is thoroughly mixed with a lithium source and a compound containing element M according to the molar ratio of the elements in the final product. The resulting mixture is sintered at high temperature to obtain an uncoated lithium-containing transition metal oxide.

[0113] Step 110,

[0114] The precipitant in precipitant solution B may include one or more of sodium hydroxide, sodium carbonate, potassium carbonate, and potassium hydroxide;

[0115] The complexing agent in solvent C may include one or more of the following: ammonia, ammonium chloride, ammonium sulfate, urea, citric acid, EDTA, etc.

[0116] The pH range in the reactor is controlled between 10.5 and 12.5, and the reaction temperature is between 40°C and 80°C.

[0117] Step 110, the volume average particle size D of the ternary material precursor v 50 ranges from 6μm to 18μm, with options from 8μm to 12μm.

[0118] Step 120: Element M may include one or more of the following: B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, Se, etc., and compounds containing element M may include one or more of the following: oxides, hydroxides, carbonates, sulfates, nitrates, chlorides, fluorides, etc., containing element M.

[0119] Step 120: The lithium source may include one or more of the following: LiOH·H2O, Li2CO3, Li2SO4, LiNO3, LiC2O4, and CH3COOLi.

[0120] The molar ratio of the lithium source to the metal in the ternary material precursor is fed according to the molar ratio of the final product.

[0121] In step 120, the sintering temperature is 600℃ to 800℃, and can be selected as 650℃ to 750℃;

[0122] In step 120, the sintering time is 8 hours to 18 hours, and can be selected as 10 hours to 15 hours;

[0123] In step 120, the heating rate is 0.5℃ / min to 5℃ / min, preferably 1℃ / min to 3℃ / min;

[0124] In step 120, the sintering atmosphere is air or oxygen.

[0125] Positive electrode

[0126] This application also proposes a positive electrode sheet.

[0127] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes any positive electrode active material in the embodiments of this application. For example, the positive current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0128] The positive electrode active material and other additives in the positive electrode film can be effectively bonded together, so that the additives can change synchronously with the volume change of the positive electrode active material, thereby effectively reducing the volume expansion of the positive electrode sheet, reducing the expansion degree of the battery cell, and improving the cycle performance of the battery cell.

[0129] In some embodiments, the positive electrode film layer includes an additive, which includes a positive electrode binder.

[0130] This application does not impose any particular limitation on the type of positive electrode binder. The positive electrode binder includes one or more of fluoropolymers and acrylate resins. Optionally, the positive electrode binder includes a fluoropolymer. The above-mentioned positive electrode binder can effectively cooperate with the polymer in the positive electrode active material, improve the connection ability between the positive electrode active material and the positive electrode binder, achieve synchronous volume change of the positive electrode active material and the positive electrode binder, and reduce the expansion degree of the positive electrode sheet.

[0131] As an example, fluorinated polymers may include one or more of polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, and a copolymer of tetrafluoroethylene-hexafluoropropylene. As an example, acrylate resins include one or more of polymethyl fluoride and polyacrylate.

[0132] In some implementations, the mass content of the positive electrode binder is ≤5% based on the mass of the positive electrode film.

[0133] In some embodiments, the positive electrode film layer further includes a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode conductive agent is ≤5%.

[0134] The positive electrode film layer includes a positive electrode active material, which may be a positive electrode active material known in the art for use in battery cells. As an example, the positive electrode active material may include one or more of the following materials: layered structure positive electrode active materials (e.g., ternary, lithium nickel oxide / sodium, lithium cobalt oxide / sodium, lithium manganese oxide / sodium, lithium-rich / sodium layered and rock salt phase layered materials, etc.), olivine-type phosphate active materials, spinel structure positive electrode active materials (e.g., spinel lithium manganese oxide, spinel lithium nickel manganese oxide, lithium-rich spinel lithium manganese oxide and lithium nickel manganese oxide, etc.).

[0135] In the embodiments of this application, the aforementioned positive electrode active materials can also be modified compounds, which can be doped and / or surface-coated modified by doping the positive electrode active materials. For example, doping can be performed by doping with transition metal elements, or coating can be performed by coating the material surface with a carbon layer.

[0136] In some embodiments, the positive electrode active material includes a core and a coating layer, the core comprising a lithium-containing transition metal oxide, and the coating layer covering at least a portion of the surface of the core, the coating layer comprising a polymer.

[0137] Optionally, lithium-containing transition metal oxides include those with the general formula Li x A y Ni a Co b Mn c M (1-a-b-c) Q z Compounds wherein 0 < x ≤ 2.1, 0 ≤ y ≤ 2.1, and 0.9 ≤ x + y ≤ 2.1; 0 < a < 1, 0 < b < 1, 0 ≤ c < 1, and 0.1 ≤ a + b + c ≤ 1; 1.8 ≤ z ≤ 3.5; A includes one or more of Na, K, and Mg; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, and Se; Q includes one or more of O and F.

[0138] Optionally, 0.6 ≤ a < 1; further optionally, 0.8 ≤ a < 1; further optionally, 0.8 ≤ a ≤ 0.95. The theoretical specific capacity of the above-mentioned lithium-containing transition metal oxides is relatively high, which is beneficial to improving the energy density of battery cells.

[0139] In some implementations, the mass content of the positive electrode active material is 80% to 98% based on the mass of the positive electrode film.

[0140] In some implementations, the positive electrode is opaque when folded three times or more. The positive electrode can also be opaque when folded three, four, five, or six times, etc.

[0141] The flexibility of the positive electrode film can be characterized by visually inspecting the light to determine whether the positive electrode sheet is translucent. Specifically, the positive electrode sheet can be folded in half multiple times. The first fold is recorded as the first fold, the second fold in the opposite direction is recorded as the second fold, the third fold in the opposite direction is recorded as the third fold, and so on. After each fold, observe whether the crease is translucent.

[0142] In some embodiments, the cohesive force of the positive electrode film is greater than or equal to 0.7 MPa, and can be selected from 0.72 MPa to 0.85 MPa, for example 0.70 MPa, 0.71 MPa, 0.72 MPa, 0.73 MPa, 0.74 MPa, 0.75 MPa, 0.76 MPa, 0.77 MPa, 0.78 MPa, 0.79 MPa, 0.80 MPa, 0.81 MPa, 0.82 MPa, 0.83 MPa, 0.84 MPa, 0.85 MPa, or any range of two of the above values.

[0143] In this embodiment, the cohesive force of the positive electrode film can be tested using equipment and methods known in the art. Specifically, the positive electrode sheet is cut into test specimens with dimensions of 20*100mm² for later use. The side of the specimen to be tested is adhered with double-sided tape and compacted with a pressure roller to ensure that the double-sided tape is completely adhered to the positive electrode film in the specimen. The other side of the double-sided tape of the specimen is adhered to the stainless steel surface. One end of the specimen is bent in the opposite direction at a bending angle of 180°. A high-speed rail tensile testing machine is used. One end of the stainless steel is fixed to the lower clamp of the tensile testing machine, and the bent end of the specimen is fixed to the upper clamp. The angle of the specimen is adjusted to ensure that the upper and lower ends are in a vertical position. Then, the specimen is stretched at a speed of 50mm / min until the specimen is completely peeled off from the substrate. The displacement and force during the process are recorded. It is generally believed that the force when the forces are balanced is the cohesive force of the positive electrode film. The cohesive force of the positive electrode film can be used to characterize the adhesion force inside the positive electrode film.

[0144] In some embodiments, the full-charge expansion rate of the positive electrode is less than or equal to 6%, and can be selected as less than or equal to 4.9%, for example, 6%, 5.5%, 5%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, 1%, 0.5%, 0.2%, 0.1%, 0.05%, 0.02%, 0.01%, or any combination of two of the above values. A relatively small expansion rate of the positive electrode is beneficial for reducing the overall expansion rate of the battery cell.

[0145] In some embodiments, the positive current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer substrate and a metal material layer formed on at least one surface of the polymer substrate. As an example, the metal material layer may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0146] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0147] battery cell

[0148] This application also proposes a battery cell.

[0149] The battery cell includes a positive electrode as described in any embodiment of this application. The positive electrode exhibits relatively small volume expansion, which reduces the degree of expansion of the battery cell and improves its cycle performance.

[0150] [Negative electrode plate]

[0151] A single battery cell also includes a negative electrode plate.

[0152] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0153] The negative electrode active material may be any negative electrode active material known in the art for use in battery cells. As an example, the negative electrode active material may include, but is not limited to, one or more of carbon materials (e.g., carbon materials include at least one of natural graphite, artificial graphite, soft carbon, and hard carbon), silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide, and tin alloys.

[0154] In some implementations, the negative electrode active material includes silicon and carbon.

[0155] Carbon exists in one or more forms, either synthetic or natural graphite. Silicon exists in the form of silicon-based materials.

[0156] In some embodiments, the silicon content in the silicon-based material of the negative electrode film is 1% to 50% by mass, optionally 1% to 32%, for example 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 50%, or any combination of two of the above values. When the silicon content is within the above range, the theoretical specific capacity of the negative electrode active material is relatively high, which can effectively improve the energy density of the battery cell.

[0157] The combination of silicon with the aforementioned mass content and layered transition metal oxides, especially when high silicon content is combined with high nickel content (0.6≤a<1) layered transition metal oxides, can further improve the energy density of the battery cell.

[0158] When the battery cell is cylindrical, a wound electrode assembly is typically used. Wound electrode assemblies have limited residual space, particularly between the positive electrode and the separator, and even less, if any, between the negative electrode and the separator. During charging, active ions from the positive electrode material embed into the negative electrode material, causing it to expand. Since the negative electrode material contains a large amount of silicon, and silicon expands more significantly, the residual space in the wound electrode assembly is further reduced. In this situation, if the positive electrode expands excessively, it will further exacerbate the overall expansion of the electrode assembly, making the battery cell expansion even more severe. However, in the embodiments of this application, the surface of the positive electrode material is coated with a polymer. Under the action of the polymer, the expansion of the positive electrode is reduced, thereby reducing the overall expansion of the battery cell and improving its cycle performance.

[0159] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose particular limitations on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the negative electrode conductive agent is ≤5% based on the total weight of the negative electrode film layer.

[0160] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose particular limitations on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass content of the negative electrode binder is ≤5 wt% based on the total weight of the negative electrode film layer.

[0161] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass content of other additives is ≤2% based on the total weight of the negative electrode film.

[0162] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer substrate and a metal material layer formed on at least one surface of the polymer substrate. As an example, the metal material in the metal material layer may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0163] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0164] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0165] Electrolyte

[0166] In some implementations, the battery cell also includes an electrolyte.

[0167] During the charging and discharging process of a single battery cell, active ions repeatedly insert and extract between the positive and negative electrode plates, while the electrolyte acts as a conductor for these active ions. The embodiments of this application do not impose any particular restrictions on the type of electrolyte; it can be selected according to actual needs.

[0168] The electrolyte solution includes an electrolyte salt and a solvent. The types of the electrolyte salt and the solvent are not particularly limited and can be selected according to actual needs.

[0169] When the battery cell in the embodiments of this application is a lithium-ion battery, as an example, the electrolyte salt may include, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0170] When the battery cell in the embodiments of this application is a sodium-ion battery, as an example, the electrolyte salt may include, but is not limited to, one or more of the following: sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium dioxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodioxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0171] As an example, the solvent may include, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0172] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0173] The qualitative and quantitative analysis of each substance or element in this application can be performed using suitable equipment and methods known to those skilled in the art. Relevant testing methods can be referenced from domestic and international testing standards and enterprise standards. Furthermore, those skilled in the art can adaptively modify certain testing steps / instrument parameters from the perspective of testing accuracy to obtain more accurate results. One testing method can be used for qualitative or quantitative analysis, or several testing methods can be used in combination for qualitative or quantitative determination.

[0174] In the embodiments of this application, the types and contents of inorganic components / lithium salt concentrations in the electrolyte are well-known in the art and can be detected using equipment and methods known in the art. For example, the concentrations of inorganic components / lithium salts in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography analysis using standard JY / T020-1996 "General Rules for Ion Chromatography Analysis". In the embodiments of this application, freshly prepared electrolyte can be used as a sample, or a fully discharged battery (discharged to the lower limit cutoff voltage so that the battery's state of charge is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be used as a sample for detection by ion chromatography analysis.

[0175] In the embodiments of this application, the types and contents of organic components in the electrolyte are defined in the art and can be detected using equipment and methods known in the art. For example, the organic components in the electrolyte can be qualitatively and quantitatively analyzed by gas chromatography using GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents". In the embodiments of this application, freshly prepared electrolyte can be used as a sample, or a fully discharged battery (discharged to the lower limit cutoff voltage so that the battery's state of charge is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be used as a sample for detection using ion chromatography.

[0176] [Isolation membrane]

[0177] The battery cell also includes a separator.

[0178] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0179] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0180] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly by a winding process and / or a stacking process, and can be selected as a wound electrode assembly.

[0181] The embodiments of this application do not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape, with a cylindrical shape being a possible choice. As shown in Figures 1 and 2, a cylindrical battery cell 7 is used as an example.

[0182] In some embodiments, the battery cell 7 may include a housing 20.

[0183] In some embodiments, the casing 20 of the battery cell 7 can be a rigid casing, such as a hard plastic casing, an aluminum casing, a steel casing, etc. The casing 20 of the battery cell 7 can also be a pouch, such as a pouch-type pouch. The material of the pouch can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0184] The outer shell 20 is a hollow structure, and the outer shell 20 can be used to encapsulate the electrode assembly 10 and the electrolyte.

[0185] The method for preparing the battery cell 7 according to the embodiments of this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a battery cell 7. As an example, the positive electrode, the separator, and the negative electrode can be formed into an electrode assembly 10 by a winding process and / or a stacking process. The electrode assembly 10 is placed in a housing 20, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, shaping, and other processes, the battery cell 7 is obtained.

[0186] In some embodiments, the housing 20 includes a housing 21 and an end cap 22, the housing 21 having an opening and the end cap 22 closing the opening.

[0187] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 is a cylindrical structure, a cylindrical housing can be selected; if the electrode assembly 10 is a cuboid structure, a cuboid housing can be selected. Optionally, both the electrode assembly 10 and the housing 21 are cylindrical. In this case, the battery cell 7 is a cylindrical battery cell, the axial direction of the electrode assembly 10 is parallel to the axial direction of the cylindrical battery cell, and the radial direction of the electrode assembly 10 is parallel to the radial direction of the cylindrical battery cell.

[0188] In some embodiments, the housing 21 includes a sidewall 212 and an endwall 211 connected to the sidewall 212. The endwall 211 and the end cap 22 are opposite each other along the axial direction of the battery cell 7. The end cap 22 is connected to the sidewall 212, and the sidewall 212 is disposed around the electrode assembly 10.

[0189] In some embodiments, the dimension of the housing 20 along the axial direction of the electrode assembly 10 is 1.3 to 2.5 times the dimension of the housing 20 along the radial direction of the electrode assembly 10, for example, 1.3 times, 1.4 times, 1.5 times, 1.6 times, 1.7 times, 1.8 times, 1.9 times, 2.0 times, 2.1 times, 2.2 times, 2.3 times, 2.4 times, 2.5 times, or any combination of two of the above values.

[0190] In some embodiments, the axial dimension of the housing 20 is from 50 mm to 150 mm, for example, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, 110 mm, 120 mm, 130 mm, 140 mm, 150 mm or any combination of two of the above values.

[0191] In some embodiments, the radial dimension of the housing 20 is 40 mm to 80 mm. For example, the radial dimension of the battery cell 7 is 50 mm, 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, 70 mm, 75 mm, 80 mm, or any combination of two of the above values.

[0192] In some embodiments, end wall 211 and side wall 212 may have the same polarity.

[0193] In some embodiments, the end wall 211 and the side wall 212 may be integrally formed, that is, the housing 21 is a one-piece component. Of course, the end wall 211 and the side wall 212 may also be two separate components, which are then connected together by welding, riveting, bonding or other methods.

[0194] From the external shape of the electrode assembly 10, the electrode assembly 10 includes a main body 12, a first electrode tab 111, and a second electrode tab 112, which protrude from the main body 12. The first electrode tab 111 is the portion of the first electrode sheet that is not coated with an active material layer, and the second electrode tab 112 is the portion of the second electrode sheet that is not coated with an active material layer. The first electrode tab 111 and the second electrode tab 112 are used to draw current from the main body 12. The first electrode sheet and the second electrode sheet have opposite polarities; in other words, one of the first electrode sheet and the second electrode sheet is a positive electrode sheet, and the other of the first electrode sheet and the second electrode sheet is a negative electrode sheet.

[0195] Taking the first tab 111 as the negative electrode tab and the second tab 112 as the positive electrode tab as an example, the portion of the negative electrode current collector in the negative electrode sheet that is not coated with an active material layer is the negative electrode tab. The active material coated on the negative electrode current collector in the negative electrode sheet constitutes the negative electrode film layer. The negative electrode film layer and the negative electrode current collector coated with active material are not considered part of the main body 12. Similarly, the portion of the positive electrode current collector in the positive electrode sheet that is not coated with an active material layer is the positive electrode tab. The active material coated on the positive electrode current collector in the positive electrode sheet constitutes the positive electrode film layer. The positive electrode film layer and the positive electrode current collector coated with active material are part of the main body 12.

[0196] In some embodiments, the battery cell 7 includes a first electrode lead-out portion and a second electrode lead-out portion, the first electrode lead-out portion being electrically connected to a first tab 111, and the second electrode lead-out portion being electrically connected to a second tab 112.

[0197] In the axial direction of the main body 12, the first electrode lead-out portion and the second electrode lead-out portion may also be located on both sides of the electrode assembly 10, or the first electrode lead-out portion and the second electrode lead-out portion may be located on the same side of the electrode assembly 10. For example, the second electrode lead-out portion includes an electrode terminal 30 insulated on the end wall 211, and the first electrode lead-out portion is the end wall 211.

[0198] The first tab 111 and the second tab 112 can extend from the same side of the main body 12, or they can extend from opposite sides respectively.

[0199] The first electrode tab 111 and the second electrode tab 112 may be respectively disposed on both sides of the main body 12 along the axial direction. In other words, the first electrode tab 111 and the second electrode tab 112 are respectively disposed at both ends of the electrode assembly 10 along the axial direction.

[0200] Optionally, the first tab 111 is wound multiple times around the central axis of the electrode assembly 10, and the first tab 111 includes multiple tab layers. After winding, the first tab 111 is generally cylindrical, with gaps between adjacent tab layers. Embodiments of this application can process the first tab 111 to reduce the gaps between tab layers, facilitating connection between the first tab 111 and other conductive structures. For example, embodiments of this application can flatten the first tab 111 so that the end regions of the first tab 111 away from the main body 12 are gathered together; the flattening process forms a dense end face at the end of the first tab 111 away from the main body 12, reducing the gaps between tab layers and facilitating connection between the first tab 111 and other conductive structures. Alternatively, embodiments of this application can also fill the gaps between adjacent tab layers with conductive material to reduce the gaps between tab layers.

[0201] Optionally, the second tab 112 is wound around the central axis of the electrode assembly 10 multiple times, and the second tab 112 includes multiple tab layers. Exemplarily, the second tab 112 is also flattened to reduce the gaps between the tab layers of the second tab 112.

[0202] The first tab 111 is electrically connected to the end cap 22. The first tab 111 can be directly electrically connected to the end cap 22, or it can be indirectly electrically connected to the end cap 22 through other conductive structures. The end cap 22 is electrically connected to the end wall 211.

[0203] The second tab 112 is electrically connected to the electrode terminal 30 of the battery cell 7, and the electrode terminal 30 is insulated from the end wall 211. The second tab 112 can be directly electrically connected to the electrode terminal 30, or it can be indirectly electrically connected to the electrode terminal 30 through other conductive structures.

[0204] In some embodiments, the second tab 112 can be directly connected to the electrode terminal 30, for example, by welding, abutting, or other means. Alternatively, the second tab 112 can also be indirectly connected to the electrode terminal 30 via other conductive components (e.g., current collector 40) to achieve electrical connection between the second tab 112 and the electrode terminal 30.

[0205] The electrode terminal 30 is insulated from the end wall 211. Therefore, the electrode terminal 30 and the end wall 211 can have different polarities and can serve as different output poles.

[0206] The end wall 211 may be provided with an electrode lead-out hole. The electrode terminal 30 is insulated on the end wall 211 and installed in the electrode lead-out hole. The electrode lead-out hole facilitates the lead-out of the electrical energy of the electrode assembly 10 to the outside of the housing 21.

[0207] The central axis of the electrode assembly 10 is a virtual straight line. The central axis of the electrode assembly 10 can pass through the electrode lead-out hole or be offset from the electrode lead-out hole. This application does not limit this.

[0208] The electrode terminal 30 can be fixed to the end wall 211. The electrode terminal 30 can be fixed as a whole to the outside of the end wall 211, or it can extend into the inside of the housing 20 through the electrode lead-out hole.

[0209] When the first tab 111 is the negative tab and the second tab 112 is the positive tab, the end wall 211 is the negative output terminal of the battery cell 7, and the electrode terminal 30 is the positive output terminal of the battery cell 7.

[0210] As shown in Figure 3, in some embodiments of this application, the battery cell 7 according to the implementation of this application can be assembled into a battery module 6. The number of battery cells 7 contained in the battery module 6 can be one or more, and the specific number can be adjusted according to the application and capacity of the battery module 6.

[0211] If there are multiple battery cells 7, they can be connected in series, parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells 7 are connected in both series and parallel configurations. Multiple battery cells 7 can be directly connected in series, parallel, or in a mixed configuration, and then the entire assembly of the multiple battery cells 7 is housed within the housing of the battery module 6. Alternatively, multiple battery cells 7 can first be connected in series, parallel, or in a mixed configuration to form the battery module 6, and then the multiple battery modules 6 can be connected in series, parallel, or in a mixed configuration to form a whole, which is then housed within the housing. Multiple battery cells 7 can be electrically connected via a busbar component, which includes a first connecting member and a second connecting member. The first connecting member is used to connect to the end wall 211 of the battery cell 7, and the second connecting member is used to connect to the electrode terminal 30 of the battery cell 7.

[0212] The first connecting member can be connected to the end wall 211 by welding, bonding or other means to achieve electrical connection between the first connecting member and the end wall 211.

[0213] The second connecting member can be connected to the electrode terminal 30 by welding, bonding, riveting or other means to achieve electrical connection between the first connecting member and the electrode terminal 30.

[0214] In this embodiment, by using the end wall 211 and the electrode terminal 30 as the output poles, the structure of the battery cell 7 can be simplified while ensuring the current carrying capacity of the battery cell 7. Since the end wall 211 and the electrode terminal 30 are located at the same end of the battery cell 7, the first connecting member and the second connecting member can be assembled onto the same side of the battery cell 7, thus simplifying the assembly process and improving the efficiency of assembling multiple battery cells 7 into a group.

[0215] Optionally, the battery module 6 may also include a receiving portion with a receiving space in which multiple battery cells 7 are received.

[0216] As shown in Figure 4, in some embodiments, the battery module 6 can also be assembled into a battery 2, and the number of battery modules 6 contained in the battery 2 can be adjusted according to the application and capacity of the battery pack.

[0217] The battery 2 may include a housing 5 and a plurality of battery modules 6 disposed within the housing 5. The housing 5 includes a first housing portion 5a and a second housing portion 5b, and the housing 5 has a receiving space 5c. The first housing portion 5a is used to cover the second housing portion 5b, forming a closed space for accommodating the battery modules 6. The plurality of battery modules 6 can be arranged in the housing 5 in any manner.

[0218] The first housing portion 5a and the second housing portion 5b overlap each other, and together they define a receiving space 5c for accommodating a single battery cell. The second housing portion 5b can be a hollow structure with one open end, and the first housing portion 5a can be a plate-like structure. The first housing portion 5a covers the open side of the second housing portion 5b to form a housing 5 with the receiving space 5c. Alternatively, both the first housing portion 5a and the second housing portion 5b can be hollow structures with one open side, with the open side of the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the receiving space 5c. Of course, the first housing portion 5a and the second housing portion 5b can be of various shapes, such as cylinders, cuboids, etc.

[0219] To improve the sealing performance after the first housing part 5a and the second housing part 5b are connected, a sealing element, such as sealant or sealing ring, can also be provided between the first housing part 5a and the second housing part 5b.

[0220] Assuming that the first box section 5a covers the top of the second box section 5b, the first box section 5a can also be called the upper box cover, and the second box section 5b can also be called the lower box.

[0221] Electrical appliances

[0222] A third aspect of this application provides an electrical device, which includes at least one of the battery cell, battery module, or battery pack described in this application. The battery cell, battery module, or battery pack can be the power source of the electrical device or the energy storage unit of the electrical device. The electrical device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, and power tool, etc. Vehicles can be gasoline-powered vehicles, natural gas-powered vehicles, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.; spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc.; electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc.; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the above-described electrical device.

[0223] Electrical devices can be equipped with individual battery cells, battery modules, or battery packs depending on their usage requirements.

[0224] Figure 5 is a schematic diagram of an example electrical device 1. This electrical device 1 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device 1, a battery pack or battery module can be used.

[0225] The electrical device 1 has a battery 2 installed inside it. The battery 2 can be located at the bottom, head, or tail of the electrical device 1. The battery 2 can be used to supply power to the electrical device 1. For example, the battery 2 can be used as the operating power source of the electrical device 1, and it can also be used as the driving power source of the electrical device 1, replacing or partially replacing fuel oil or natural gas to provide driving power for the electrical device 1.

[0226] Electrical device 1 may also include controller 3 and motor 4. Controller 3 is used to control battery 2 to supply power to motor 4, for example, to meet the power needs of electrical device 1 during startup, navigation and driving.

[0227] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0228] Example

[0229] The following examples describe the disclosure of the present invention in more detail. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present invention will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0230] Example 1

[0231] 1. Preparation of positive electrode sheet

[0232] The positive electrode sheet includes a positive current collector and a positive electrode film layer. The positive electrode film layer is located on both sides of the positive current collector. The positive current collector is an aluminum foil. The positive electrode film layer is formed by uniformly coating the surface of the positive current collector aluminum foil with a positive electrode slurry (solvent is N-methylpyrrolidone NMP), and then drying and cold pressing it. The positive electrode film layer includes positive active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) in a weight ratio of 96.5:2:1.5.

[0233] The positive electrode active material includes a core and a coating layer covering the surface of the core. The core includes materials with the molecular formula LiNi. 0.92 Co 0.07 Mn 0.01The compound of O2 (NCM9271) has a coating layer consisting of a first layer and a second layer. The preparation steps of the positive electrode active material are as follows:

[0234] After mixing the core and the fast ion conductor source cobalt oxide, the mixture is treated at 600°C for 5 hours. The fast ion conductor source forms a fast ion conductor that coats the surface of the core, forming the first layer. The first layer and the core constitute the intermediate particles.

[0235] After mixing the intermediate particles with polyethylene glycol, the mixture is heat-treated at 300°C. The polyethylene glycol melts and coats the core surface. After cooling to room temperature, the polyethylene glycol forms a second layer.

[0236] 2. Preparation of negative electrode sheet

[0237] The negative electrode sheet includes a negative current collector and a negative electrode film layer. The negative electrode film layer is located on both sides of the negative current collector. The negative current collector is a copper foil. The negative electrode film layer is formed by uniformly coating the surface of the copper foil of the negative current collector with negative electrode slurry (solvent is deionized water), and then drying and cold pressing. The negative electrode film layer includes negative electrode active material, styrene-butadiene rubber (SBR) binder, sodium carboxymethyl cellulose (CMC-Na) thickener, and acetylene black conductive agent in a weight ratio of 96.2:1.8:1.2:0.8.

[0238] The negative electrode active materials include artificial graphite and silicon-based materials (specifically silicon oxides), and the silicon content in the negative electrode film is 3%.

[0239] 3. Separating membrane

[0240] The release liner is a polypropylene (PP) film layer.

[0241] 4. Preparation of electrolyte

[0242] The electrolyte includes an organic solvent and a lithium salt. The organic solvent consists of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1. The lithium salt is 1 mol / L lithium hexafluorophosphate.

[0243] 5. Preparation of battery cells

[0244] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The positive electrode, separator, and negative electrode are then wound to obtain a cylindrical electrode assembly. The cylindrical electrode assembly is placed in an outer casing, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a cylindrical battery cell is obtained.

[0245] Example 2-1 to Example 2-5

[0246] Battery cells were prepared using a method similar to that of Example 1, except that the material of the second layer of the coating in the positive electrode active material was adjusted.

[0247] Examples 3-1 to 3-5

[0248] Battery cells were prepared using a method similar to that of Example 1, except that the mass content of the second layer of the coating in the positive electrode active material was adjusted.

[0249] Examples 4-1 to 4-3

[0250] Battery cells were prepared using a method similar to that of Example 1, except that the material of the first layer of the coating in the positive electrode active material was adjusted.

[0251] Examples 5-1 to 5-4

[0252] Battery cells were prepared using a method similar to that of Example 1, except that the mass content of the first layer of the coating in the positive electrode active material was adjusted.

[0253] Examples 6-1 and 6-2

[0254] Battery cells were prepared using a method similar to that of Example 1, except that the volume average particle size of the positive electrode active material was adjusted.

[0255] Examples 7-1 and 7-2

[0256] Battery cells were prepared using a method similar to that of Example 1, except that the material of the core in the positive electrode active material was adjusted.

[0257] In Example 7-1, the core comprises a compound with the molecular formula LiN. i0.8 Co 0.1 Mn 0.1 Compounds of O2;

[0258] In Example 7-2, the core comprises a compound with the molecular formula LiNi. 0.95 Co 0.04 Mn 0.01 Compounds of O2.

[0259] Comparative Example 1

[0260] Battery cells were prepared using a method similar to that of Example 1. The difference from Example 1 is that the positive electrode active material did not have a coating layer. The positive electrode active material included materials with the molecular formula LiNi. 0.92 Co 0.07 Mn 0.01 Compounds of O2 (NCM9271).

[0261] Comparative Example 2

[0262] Battery cells were prepared using a method similar to that of Example 1. The difference from Example 1 is that the positive electrode active material includes a core and a coating layer covering the surface of the core. The core comprises a material with the molecular formula LiNi. 0.92 Co 0.07 Mn 0.01 The O2 (NCM9271) compound, with a coating layer including a first layer, and the preparation steps of the positive electrode active material are as follows:

[0263] After mixing the core and the fast ion conductor source cobalt oxide, the mixture is treated at 600°C for 5 hours. The fast ion conductor source forms a fast ion conductor that coats the surface of the core, forming the first layer. The first layer and the core constitute the positive electrode active material.

[0264] Comparative Example 3

[0265] Battery cells were prepared using a method similar to that of Example 1, except that the material of the second layer of the coating in the positive electrode active material was adjusted.

[0266] Performance testing

[0267] 1. Positive electrode full-charge expansion rate test

[0268] Multiple battery cells were prepared according to the method in Example 1. One of the multiple battery cells was fully charged to 4.25V at 0.33C and then charged at a constant voltage of 4.25V until the current was ≤0.05mA. Subsequently, the battery cell was disassembled and the positive electrode sheet was removed. Its thickness was measured as a, in μm.

[0269] One of the multiple battery cells was fully discharged to 2.8V at 0.33C. The battery cell was then disassembled and the positive electrode was removed. Its thickness was measured as b, in μm.

[0270] The full-charge expansion rate of the positive electrode is [(ab) / b]. × 100%.

[0271] Other embodiments and comparative examples were tested according to the test method for the full-charge expansion rate of the positive electrode sheet in Example 1.

[0272] 2. Cycle performance of individual battery cells at 25℃

[0273] In a constant temperature environment of 25°C, the battery cells prepared in the examples and comparative examples were charged to 4.25V at 1C, and then charged at 4.25V at a constant voltage until the current was ≤0.05mA. After standing for 5 minutes, they were discharged to 2.8V at 1C. The capacity was recorded as Dn (n=0, 1, 2……). The previous process was repeated until the capacity decayed to 80%, and the number of cycles was recorded.

[0274] 3. Cycle performance of individual battery cells at 45℃

[0275] In a constant temperature environment of 45°C, the battery cells prepared in the examples and comparative examples were charged to 4.25V at 1C, and then charged at 4.25V at a constant voltage until the current was ≤0.05mA. After standing for 5 minutes, they were discharged to 2.8V at 1C. The capacity was recorded as Dn (n=0, 1, 2……). The previous process was repeated until the capacity decayed to 80%, and the number of cycles was recorded.

[0276] 4. Energy density of a single battery cell

[0277] The battery cells prepared in the example were charged at a constant current of 1C to 4.25V, then charged at a constant voltage of 0.05C, left to stand for 30 minutes, and then discharged at 1C to 2.8V. The discharge capacity D0 was recorded. The volume of the battery cells was measured and the volume V0 was recorded. The energy density of the battery cells was D0 / V0 (capacity per unit volume).

[0278] The volumetric energy density of the battery cell in Example 1 is 650Wh / L;

[0279] The volumetric energy density of the battery cell in Example 7-1 is 600Wh / L;

[0280] The volumetric energy density of the battery cell in Example 7-2 is 700Wh / L.

[0281] Test Results

[0282] The test results are shown in Table 1.

[0283] Table 1

[0284] As can be seen from Table 1,

[0285] In Comparative Example 1, the positive electrode active material was not coated, and the full-charge expansion rate of the positive electrode sheet in Comparative Example 1 was relatively high, and the cycle performance was poor.

[0286] In Comparative Example 2, the positive electrode active material includes a fast ion conductor layer, which can effectively improve the lithium ion extraction rate, reduce the degree of expansion to a certain extent, and improve cycle performance. Comparative Example 3, based on Comparative Example 2, also includes a polyaniline layer. The addition of the polyaniline layer may worsen the impedance, leading to a deterioration in battery performance and a decrease in cycle performance.

[0287] In this embodiment, a coating layer is provided on the surface of the core. The coating layer includes a first layer, which includes a fluoropolymer and an oxygen-containing polymer. The first layer can effectively connect the positive electrode active material and the binder, so that the binder can change synchronously with the volume change of the positive electrode active material, thereby effectively reducing the volume expansion of the positive electrode sheet, reducing the expansion degree of the battery cell, and improving the cycle performance of the battery cell.

[0288] By adjusting the materials of the polymer and / or the fast ion conductor, the volume expansion of the positive electrode sheet can be effectively controlled, and the cycle performance of the battery cell can be effectively improved. For example, polyethylene glycol can reduce the brittleness of PVDF and effectively connect the positive electrode active material and PVDF, allowing the PVDF to change synchronously with the volume change of the positive electrode active material. In Examples 1, 3-1 to 3-5, by adjusting the polymer coating amount (polymer mass content), especially when the polymer mass content is between 0.15% and 1.00%, the volume expansion of the positive electrode sheet is small, and the cycle performance is effectively improved.

[0289] Examples 1 and 5-1 to 5-4 show that by adjusting the coating amount (mass content of fast ion conductor), especially when the mass content of fast ion conductor is between 0.50% and 2.50%, the volume expansion of the positive electrode is small, and the cycle performance is effectively improved. As the content of fast ion conductor increases, the volume ratio of the core decreases, and the improvement in energy density is limited. Therefore, when the mass content of fast ion conductor is between 0.50% and 2.50%, both cycle performance and energy density of the battery can be balanced.

[0290] The coating layer is suitable for cores of different materials and / or different particle sizes. The volume average particle size of the positive electrode active material formed after the coating layer coats the core is 5μm to 15μm, especially 7μm to 12μm, and can be further selected as 9μm to 12μm. The volume expansion of the positive electrode sheet is small and the cycle performance is effectively improved.

[0291] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting this application, and that the embodiments can be changed, substituted and modified without departing from the spirit, principles and scope of this application.

Claims

1. A positive electrode active material, comprising a core and a coating layer, the core comprising a lithium-containing transition metal oxide, the coating layer covering at least a portion of the surface of the core, the coating layer comprising a polymer, the polymer comprising one or more of fluoropolymers and oxygen-containing polymers.

2. The positive electrode active material according to claim 1, wherein, The fluoropolymers include one or more of polyvinylidene fluoride, polytetrafluoroethylene, ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

3. The positive electrode active material according to claim 1 or 2, wherein, The oxygen-containing polymers include one or more of ether polymers and ester polymers.

4. The positive electrode active material according to claim 3, wherein, The ether polymer includes one or more of polyethylene glycol and polypropylene glycol; and / or The ester polymers include one or more of polyvinyl acetate and polymethyl methacrylate.

5. The positive electrode active material according to any one of claims 1 to 4, wherein, The polymer has a mass content of 0.15% to 1.0% in the positive electrode active material.

6. The positive electrode active material according to claim 5, wherein, The polymer has a mass content of 0.15% to 0.7% in the positive electrode active material.

7. The positive electrode active material according to any one of claims 1 to 6, wherein, The coating layer also includes a fast ion conductor.

8. The positive electrode active material according to claim 7, wherein, The fast ion conductor has a mass content of 0.5% to 2.5% in the positive electrode active material.

9. The positive electrode active material according to claim 8, wherein, The fast ion conductor has a mass content of 0.5% to 2.0% in the positive electrode active material.

10. The positive electrode active material according to any one of claims 7 to 9, wherein, The coating layer includes: A first layer, covering the surface of the core, the first layer including the fast ion conductor; and The second layer is disposed on the side of the first layer opposite to the core, and the second layer includes the polymer.

11. The positive electrode active material according to any one of claims 1 to 10, wherein, The lithium-containing transition metal oxide includes those with the general formula Li x A y Ni a Co b Mn c M (1-a-b-c) Q z Compounds wherein 0 < x ≤ 2.1, 0 ≤ y ≤ 2.1, and 0.9 ≤ x + y ≤ 2.1; 0 < a < 1, 0 < b < 1, 0 ≤ c < 1, and 0.1 ≤ a + b + c ≤ 1; 1.8 ≤ z ≤ 3.5; A includes one or more of Na, K, and Mg; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, and Se; Q includes one or more of O and F.

12. The positive electrode active material according to claim 11, wherein, 0.6≤a≤1。 13. The positive electrode active material according to any one of claims 1 to 12, wherein, The volume average particle size D of the positive electrode active material v 50 ranges from 5μm to 15μm.

14. The positive electrode active material according to claim 13, wherein, The volume average particle size D of the positive electrode active material v 50 ranges from 7μm to 12μm.

15. A positive electrode sheet, comprising a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector, the positive electrode film layer comprising a positive electrode active material as described in any one of claims 1 to 14.

16. The positive electrode sheet according to claim 15, wherein, The positive electrode film layer further includes a positive electrode binder, which includes one or more of fluoropolymers and acrylate resins.

17. The positive electrode sheet according to claim 16, wherein, The fluorinated polymer includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer; and / or The acrylate resins include one or more of polymethyl fluorinated acrylate and polyacrylate.

18. A cylindrical battery cell, comprising a positive electrode sheet as described in any one of claims 15 to 17.

19. The cylindrical battery cell according to claim 18, wherein, The full-charge expansion rate of the positive electrode is less than or equal to 6%.

20. The cylindrical battery cell according to claim 19, wherein, The full-charge expansion rate of the positive electrode is less than or equal to 4.9%.

21. The cylindrical battery cell according to any one of claims 18 to 20, comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material, the negative electrode active material comprising a silicon-based material, wherein the silicon content in the negative electrode film layer is 1% to 50% by mass.

22. The cylindrical battery cell according to any one of claims 18 to 21, further comprising a housing, the housing comprising a casing and an end cap, the casing having an opening, the end cap covering the opening; The housing includes an integrally formed sidewall and an endwall, the endwall and the end cap being opposite each other along the axial direction of the cylindrical battery cell, and the end cap being connected to the sidewall.

23. The cylindrical battery cell according to claim 22, wherein the battery cell further comprises electrode terminals, the electrode terminals being insulated from the end wall; The positive electrode plate includes a positive electrode tab, which is electrically connected to the electrode terminal; The cylindrical battery cell includes a negative electrode sheet, the negative electrode sheet includes a negative electrode tab, and the negative electrode tab is electrically connected to the end cap.

24. The cylindrical battery cell according to any one of claims 18 to 23, further comprising a housing, wherein the dimension of the housing along the axial direction of the cylindrical battery cell is 1.3 to 2.5 times the dimension of the housing along the radial direction of the cylindrical battery cell.

25. The cylindrical battery cell according to claim 24, wherein, The outer casing has a dimension of 50 mm to 150 mm along the axial direction; and / or The outer casing has a radial dimension of 40 mm to 80 mm.

26. A battery comprising a cylindrical battery cell as claimed in any one of claims 18 to 25.

27. An electrical device comprising the battery as claimed in claim 26.

Images