Battery cell, battery device, energy storage device, energy storage system and electric device

Abstract

The present application relates to the technical field of batteries, and particularly relates to a battery cell, a battery device, an energy storage device, an energy storage system and an electric device. Provided in the present application is a battery cell, comprising an electrode assembly. The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator. The negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer arranged on at least one side of the negative electrode current collector. The negative electrode material layer comprises a negative electrode active material. The negative electrode active material comprises amorphous carbon-coated graphite. The amorphous carbon-coated graphite comprises a graphite inner core and an amorphous carbon coating layer on the surface of the graphite inner core, wherein the interlayer spacing of crystal planes (002) of the amorphous carbon is D1, the interlayer spacing of crystal planes (002) of the graphite inner core is D2, and 1.0<D1 / D2≤1.1. The positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer arranged on at least one side of the positive electrode current collector. The positive electrode material layer comprises a positive electrode active material. The positive electrode active material comprises a carbon-coated lithium iron phosphate material. In the Raman spectrum of the carbon-coated lithium iron phosphate material, Id / Ig≤1.5.

Description

Battery cell, battery device, energy storage device, energy storage system and power consumption device

[0001] Cross-reference to related applications

[0002] This application is based on an application with a CN application number of 202510117678.6 and a filing date of January 24, 2025, and claims its priority. The content of this CN is hereby incorporated into this application as a whole. Technical field

[0003] This application relates to the technical field of batteries, particularly to battery cells, battery devices, energy storage devices, energy storage systems and power consumption devices. Background technique

[0004] Energy storage batteries are the core equipment of energy storage systems, mainly using chemical reactions for energy storage. Energy storage requires a battery structure with large capacity, long cycle life, high safety and high energy efficiency. Currently, the market has higher and higher requirements for the lifespan of energy storage products. Summary of the invention

[0005] To solve the cycle life problem of battery cells, a first embodiment of this application provides a battery cell, including an electrode assembly. The electrode assembly includes a positive electrode tab, a negative electrode tab and a separator. The negative electrode tab includes a negative electrode current collector and a negative electrode material layer provided on at least one side of the negative electrode current collector. The negative electrode material layer contains a negative electrode active material. The negative electrode active material includes graphite coated with amorphous carbon. The graphite coated with amorphous carbon includes a graphite core and an amorphous carbon coating layer on the surface of the graphite core. Among them, the layer spacing of the (002) crystal plane of the amorphous carbon is D1, and the layer spacing of the (002) crystal plane of the graphite core is D2. 1.0 < D1 / D2 ≤ 1.1 is satisfied between D1 and D2. The positive electrode tab includes a positive electrode current collector and a positive electrode material layer provided on at least one side of the positive electrode current collector. The positive electrode material layer contains a positive electrode active material. The positive electrode active material includes lithium iron phosphate material coated with carbon. In the Raman spectrum of the lithium iron phosphate material coated with carbon, the ratio of the peak intensity Id of the D peak to the peak intensity Ig of the G peak satisfies Id / Ig ≤ 1.5.

[0006] The battery cell of this application includes graphite coated with amorphous carbon in the negative electrode tab. An amorphous carbon layer is formed on the surface of the graphite particles. The double-layer structure carbon material obtained by coating the surface of highly graphitized graphite material with low-degree graphitized amorphous carbon can, on the one hand, make the highly graphitized graphite have a large discharge capacity and at the same time have good rate performance.

[0007] The interlayer spacing of amorphous carbon materials is larger than that of graphite, which improves the diffusion performance of lithium ions within them. This is equivalent to forming a lithium-ion buffer layer on the outer surface of graphite, thereby improving the high-current charge-discharge performance of graphite materials. Simultaneously, by controlling the difference between the interlayer spacing of amorphous carbon and the interlayer spacing of the graphite core, i.e., controlling D1 / D2 ≤ 1.1, the resistance to lithium ion removal from the amorphous carbon coating layer can be reduced. Furthermore, the contact between amorphous carbon and solvents prevents graphite layer stripping caused by the co-intercalation of solvent molecules, expanding the range of electrolyte systems and improving the cycle stability of the electrode material.

[0008] The regularity of amorphous carbon-coated graphite can be represented by the ratio of the interlayer spacing D1 of the (002) crystal planes of the amorphous carbon to the interlayer spacing D2 of the (002) crystal planes of the graphite core. Within a certain range, D1 / D2 ensures the stability of the graphite's interlayer structure and reduces the diffusion resistance of lithium ions, facilitating lithium ion insertion and extraction during charging and discharging. Furthermore, the battery cell of this application includes carbon-coated lithium iron phosphate material in its positive electrode. Carbon coating effectively improves the surface electronic contact of lithium iron phosphate material, increases its electronic conductivity, and thus improves its rate performance and cycle performance. When the graphitization degree of the carbon coating layer is high, the conductivity of the carbon-coated lithium iron phosphate material can be further improved, and the reaction between the carbon coating layer and the electrolyte can be suppressed.

[0009] Therefore, by simultaneously introducing the aforementioned negative electrode active materials and positive electrode active materials into the battery, on the one hand, the active lithium consumption during battery cycling is reduced, and on the other hand, the kinetic performance of the battery is improved. Together, they can reduce the active lithium consumption and electrochemical polarization of the battery, thereby improving cycle life.

[0010] In some embodiments, according to claim 1, the ratio of the peak intensity Id of the D peak to the peak intensity Ig of the G peak in the Raman spectrum of the carbon-coated lithium iron phosphate material satisfies 0.9 ≤ Id / Ig ≤ 1.3.

[0011] In some embodiments, the negative electrode material layer includes a first negative electrode material layer and a second negative electrode material layer, wherein the first negative electrode material layer is disposed on at least one side of the negative electrode current collector, and the second negative electrode material layer is disposed on the side of the first negative electrode material layer away from the negative electrode current collector, wherein the ratio of the thickness t2 of the second negative electrode material layer to the thickness t1 of the first negative electrode material layer satisfies 2 / 3 ≤ t2 / t1 ≤ 1.5; and / or the porosity of the second negative electrode material layer is greater than the porosity of the first negative electrode material layer.

[0012] In some embodiments, the thickness t1 of the first negative electrode material layer and the thickness t2 of the second negative electrode material layer are each independently selected from 57 μm to 87 μm; and / or, the porosity of the first negative electrode material layer and the porosity of the second negative electrode material layer are each independently selected from 25% to 36%.

[0013] In some embodiments, the lithium iron phosphate material contains one or more doping elements selected from Ti, V, Mg, Zr, and Y.

[0014] In some embodiments, the positive electrode sheet has a coating areal density of 19.4–26.7 mg / cm³. 2 In some embodiments, the compaction density of the positive electrode material layer is 2.38–2.70 g / cm³. 3 .

[0015] In some embodiments, the battery cell further includes an electrolyte comprising a solvent, the solvent comprising a cyclic carbonate. In some embodiments, the solvent comprises ethylene carbonate (EC), optionally comprising 15%-25% of the mass of the electrolyte. In some embodiments, the solvent comprises propylene carbonate (PC), optionally comprising 1%-8% of the mass of the electrolyte.

[0016] The second embodiment of this application provides a battery device including a plurality of battery cells provided in the first embodiment of this application.

[0017] The third embodiment of this application provides an energy storage device, including a plurality of battery cells provided in the first embodiment of this application or a plurality of battery devices provided in the second embodiment of this application, wherein the battery cells or the battery devices are used to store or provide electrical energy.

[0018] The fourth embodiment of this application provides an energy storage system, including a power conversion device and an energy storage device provided in the third embodiment of this application, wherein the power conversion device is used to electrically connect a power generation device and the energy storage device.

[0019] The fifth embodiment of this application provides an electrical device, including a battery cell provided in the first embodiment of this application, a battery device provided in the second embodiment of this application, an energy storage device provided in the third embodiment of this application, or an energy storage system provided in the fourth embodiment of this application, wherein the battery cell or the battery device is used to store or provide electrical energy. Attached Figure Description

[0020] 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.

[0021] Figure 1 is a schematic diagram of a battery cell according to one embodiment of this application.

[0022] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1.

[0023] Figure 3 is a schematic diagram of a battery module according to one embodiment of this application.

[0024] Figure 4 is a schematic diagram of a battery pack according to one embodiment of this application.

[0025] Figure 5 is an exploded view of a battery pack according to an embodiment of this application, as shown in Figure 5.

[0026] Figure 6 is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to an embodiment of this application.

[0027] The accompanying drawings are not drawn to scale.

[0028] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 End cap. Detailed Implementation

[0029] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0030] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode active material and its manufacturing method, positive electrode sheet, negative electrode sheet, secondary battery, battery module, battery pack, and power-consuming 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.

[0031] 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.

[0032] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0033] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0034] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates 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.

[0035] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or contained.

[0036] Unless otherwise specified, the term "or" is inclusive in this application. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0037] [Battery cell]

[0038] In the embodiments of this application, the battery cell can be a secondary battery, which refers to a battery cell that can activate the active material through charging after discharging.

[0039] The battery cell can be a lithium-ion battery, a sodium lithium-ion battery, a magnesium-ion battery, etc., and the embodiments of this application are not limited thereto.

[0040] Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. During the charge and discharge process of the battery, active ions (such as lithium ions) intercalate and deintercalate between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows active ions to pass through. The electrolyte is between the positive electrode plate and the negative electrode plate, mainly to conduct active ions.

[0041] To solve the cycle life problem of the battery cell, a first embodiment of this application provides a battery cell, including an electrode assembly. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator; the negative electrode plate includes a negative current collector and a negative electrode material layer disposed on at least one side of the negative current collector. The negative electrode material layer contains a negative electrode active material, and the negative electrode active material includes graphite coated with amorphous carbon. The graphite coated with amorphous carbon includes a graphite core and an amorphous carbon coating layer on the surface of the graphite core. Among them, the layer spacing of the (002) crystal plane of the amorphous carbon is D1, and the layer spacing of the (002) crystal plane of the graphite core is D2, and 1.0 < D1 / D2 ≤ 1.1 is satisfied between D1 and D2; the positive electrode plate includes a positive current collector and a positive electrode material layer disposed on at least one side of the positive current collector. The positive electrode material layer contains a positive electrode active material, and the positive electrode active material includes a carbon-coated lithium iron phosphate material. In the Raman spectrum of the carbon-coated lithium iron phosphate material, the ratio of the peak intensity Id of the D peak to the peak intensity Ig of the G peak satisfies Id / Ig ≤ 1.5.

[0042] The battery cell of this application includes graphite coated with amorphous carbon in the negative electrode plate. An amorphous carbon layer is formed on the surface of the graphite particles. The double-layer structure carbon material obtained by coating the surface of the highly graphitized graphite material with low-degree graphitized amorphous carbon can, on the one hand, endow the highly graphitized graphite with a large discharge capacity and at the same time have good rate performance.

[0043] The interlayer spacing of amorphous carbon materials is larger than that of graphite, which improves the diffusion performance of lithium ions within them. This is equivalent to forming a lithium-ion buffer layer on the outer surface of graphite, thereby improving the high-current charge-discharge performance of graphite materials. Simultaneously, by controlling the difference between the interlayer spacing of amorphous carbon and the interlayer spacing of the graphite core, i.e., controlling D1 / D2 ≤ 1.1, the resistance to lithium ion removal from the amorphous carbon coating layer can be reduced. Furthermore, the contact between amorphous carbon and solvents prevents graphite layer stripping caused by the co-intercalation of solvent molecules, expanding the range of electrolyte systems and improving the cycle stability of the electrode material.

[0044] The regularity of amorphous carbon-coated graphite can be represented by the ratio of the interlayer spacing D1 of the (002) crystal plane of the amorphous carbon to the interlayer spacing D2 of the (002) crystal plane of the graphite core. Within a certain range, D1 / D2 can ensure the stability of the interlayer structure of graphite, while reducing the diffusion resistance of lithium ions, which is beneficial to the insertion and extraction of lithium ions during the charging and discharging process.

[0045] The interlayer spacing of the (002) crystal planes of the amorphous carbon coating and the interlayer spacing of the (002) crystal planes of the graphite core can be measured using a transmission electron microscope. The coating is randomly measured three times, and the average value is recorded as D1; ​​the graphite core is randomly measured three times, and the average value is recorded as D2. The ratio of D1 / D2 is calculated.

[0046] Amorphous carbon-coated graphite can be prepared by existing methods. An exemplary preparation method includes: mixing graphite powder with a binder (e.g., bitumen) to cover the surface of the graphite powder with the binder, then adding amorphous carbon powder, kneading the resulting mixture to soften the binder, thereby dispersing and stabilizing the amorphous carbon powder in the binder; and then performing heat treatment at high temperature in a non-oxidizing atmosphere to decompose and carbonize the binder, obtaining amorphous carbon-coated graphite. Before and after preparation, the interlayer spacing D1 of the (002) crystal plane of the amorphous carbon and the interlayer spacing D2 of the (002) crystal plane of the graphite core remain almost unchanged. Therefore, D1 and D2 can be controlled.

[0047] Meanwhile, the battery cell of this application includes carbon-coated lithium iron phosphate material in the positive electrode. Carbon coating can effectively improve the surface electronic contact of lithium iron phosphate material, increase the electronic conductivity of the material, and thus improve the rate performance and cycle performance of the material. When the graphitization degree of the carbon coating layer is high, the conductivity of the carbon-coated lithium iron phosphate material can be further improved, and the reaction between the carbon coating layer and the electrolyte can be suppressed.

[0048] The degree of graphitization of the carbon coating layer on the surface of lithium iron phosphate can be characterized by Raman spectroscopy. The D and G peaks in the Raman spectrum are characteristic peaks of carbon atom crystals, located at 1360±5 cm⁻¹, respectively. -1 and 1580±5cm-1 Nearby. The D peak represents the defects of the carbon atom crystal, which is inversely proportional to the degree of order of the carbon structure; the G peak represents the in-plane stretching vibration of the sp2 hybridization of carbon atoms, representing the graphitization degree of the carbon structure. The graphitization degree of the carbon coating layer can be reflected by the intensity ratio of the D peak to the G peak of Raman.

[0049] In the Raman spectrum of carbon-coated lithium iron phosphate, when the ratio of the peak intensity Id of the D peak to the peak intensity Ig of the G peak satisfies Id / Ig ≤ 1.5, the graphitization degree of the carbon coating layer on the surface of lithium iron phosphate is relatively high, and the electron conduction performance is good, which can improve the kinetic performance of the battery monomer.

[0050] Therefore, introducing the above-mentioned negative electrode active material and positive electrode active material into the battery simultaneously reduces the consumption of active lithium during the battery cycle on the one hand and improves the kinetic performance of the battery on the other hand. Collaboratively, it can reduce the consumption of active lithium and electrochemical polarization of the battery, thereby achieving the effect of improving the cycle life.

[0051] In some embodiments, in the amorphous carbon-coated graphite included in the negative electrode sheet, the layer spacing D1 of the (002) crystal plane of the amorphous carbon is 0.345 nm to 0.376 nm.

[0052] In some embodiments, in the amorphous carbon-coated graphite included in the negative electrode sheet, the layer spacing D2 of the (002) crystal plane of the graphite core is 0.342 nm.

[0053] In some embodiments, D1 / D2 satisfies 1.0 < D1 / D2 ≤ 1.01, 1.01 < D1 / D2 ≤ 1.03, 1.03 < D1 / D2 ≤ 1.06, 1.06 < D1 / D2 ≤ 1.08 or 1.08 < D1 / D2 ≤ 1.10.

[0054] In some embodiments, Id / Ig satisfies 0.6 ≤ Id / Ig ≤ 1.5, for example, 0.6 ≤ Id / Ig ≤ 0.9, 0.9 ≤ Id / Ig ≤ 1.1, 1.1 ≤ Id / Ig ≤ 1.3 or 1.3 ≤ Id / Ig ≤ 1.5.

[0055] In some embodiments, Id / Ig satisfies 0.9 ≤ Id / Ig ≤ 1.3. When Id / Ig is within the above range, there is a better balance ratio between carbon defects and carbon graphitization.

[0056] Refer to the standard GB / T 40219-2021, and use a LabRAM HR Evolution type laser micro-Raman spectrometer to obtain the Raman spectrum of the material. Among them, a solid laser with a wavelength of 523 nm is used as the light source, the beam diameter is 1.2 μm, and the power is 1 mW; the measurement mode is macro Raman; a CCD detector is used.

[0057] The lithium iron phosphate active material powder was compressed into tablets, and three points were randomly selected on the tablets for testing. The average value of the three sets of measurements was then taken.

[0058] [Negative electrode plate]

[0059] The negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector, the negative electrode material layer including a negative electrode active material.

[0060] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0061] In some embodiments, the negative electrode material layer includes a first negative electrode material layer and a second negative electrode material layer, wherein the first negative electrode material layer is disposed on at least one side of the negative electrode current collector, and the second negative electrode material layer is disposed on the side of the first negative electrode material layer away from the negative electrode current collector, and the ratio of the thickness t2 of the second negative electrode material layer to the thickness t1 of the first negative electrode material layer satisfies 2 / 3 ≤ t2 / t1 ≤ 1.5; and / or in some embodiments, the porosity of the second negative electrode material layer is greater than the porosity of the first negative electrode material layer.

[0062] In some embodiments, the porosity of the two layers can be adjusted by modifying the formulations of the coating slurry for the first and second negative electrode layers. For example, the coating slurry for the second negative electrode layer can have a higher conductive carbon content and a lower graphite content compared to the coating slurry for the first negative electrode layer. After coating and cold pressing, the compaction density of the second negative electrode layer will be slightly lower than that of the first negative electrode layer, thereby increasing the porosity of the second negative electrode layer.

[0063] In some embodiments, the ratio of the thickness t2 of the second negative electrode material layer to the thickness t1 of the first negative electrode material layer satisfies 2 / 3≤t2 / t1≤1 or 1≤t2 / t1≤1.5.

[0064] In some embodiments, the thickness t1 of the first negative electrode material layer and the thickness t2 of the second negative electrode material layer are each independently selected from 57μm to 87μm, for example 57μm to 60μm, 60μm to 65μm, 65μm to 70μm, 70μm to 72μm, 72μm to 80μm or 80μm to 87μm.

[0065] In some embodiments, the porosity of the first negative electrode material layer and the porosity of the second negative electrode material layer are each independently selected from 25% to 36%, for example 25% to 26%, 26% to 28%, 28% to 30%, 30% to 32%, or 32% to 36%.

[0066] The interfacial impedance of a single-layer coating is greater than that of a multi-layer coating. Using a multi-layer negative electrode material can, on the one hand, reduce the binder content in each layer's formulation, thus lowering the interfacial impedance; on the other hand, it can also improve the uniformity of binder distribution within the electrode, thereby improving current density.

[0067] The design employs a tiered porosity distribution with a sparser top and a denser bottom, which is more conducive to the full wetting of the electrolyte. The role of the electrolyte is to conduct lithium ions, which helps to accelerate the conduction speed of ions on the negative electrode surface, ultimately improving the dynamics of the battery cells and increasing cycle life.

[0068] The thickness of the first negative electrode material layer and the thickness of the second negative electrode material layer can be measured using the following methods:

[0069] Take a cross-section of the negative electrode sheet and observe it using tomographic SEM. A clear boundary line between the two coating layers can be seen. Using the boundary line as a baseline, measure the thickness from the boundary line to the current collector surface, which is the thickness of the first active layer; measure the thickness from the boundary line to the upper surface of the electrode sheet, which is the thickness of the second active layer.

[0070] The porosity of the negative electrode sheet can be measured using the following methods:

[0071] A cross-section of the negative electrode sheet was taken, and the double-layer coating structure of the negative electrode sheet was observed using tomographic SEM. A cross-sectional SEM image of a randomly selected field of view was taken, ensuring it contained the complete first and second active layers. The total area S1 of the first active layer and the total area R1 occupied by the first active material in the first active layer were measured. The porosity of the first active layer was defined as (1-R1 / S1)×100%. The total area S2 of the second active layer and the total area R2 occupied by the second active material in the second active layer were measured. The porosity of the second active layer was defined as (1-R2 / S2)×100%.

[0072] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0073] In some embodiments, the negative electrode material layer may optionally include a binder. As an example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0074] In some embodiments, the negative electrode material layer may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0075] In some embodiments, the negative electrode material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0076] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0077] [Positive electrode plate]

[0078] In some embodiments, the positive electrode may be a positive electrode sheet, which may include a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material is disposed on either or both of the two opposite surfaces of the positive current collector.

[0079] As an example, the positive current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0080] In some embodiments, the positive electrode active material includes carbon-coated lithium iron phosphate material, wherein the lithium iron phosphate material contains one or more doping elements selected from Ti, V, Mg, Zr, and Y. In some embodiments, the lithium iron phosphate contains one or more doping elements selected from Ti and V. Using lithium iron phosphate doped with the above-mentioned elements can lower the lithium-ion transport barrier, increase the lithium-ion diffusion rate, thereby improving the battery's kinetic performance and cycle performance. Ti and V doping exhibit superior performance in improving lithium-ion diffusion compared to other element doping methods.

[0081] In some embodiments, the mass percentage of dopant elements in the lithium iron phosphate material is 0.02% to 0.4% (e.g., 0.02% to 0.1%, 0.1% to 0.2%, 0.2% to 0.3%, or 0.3% to 0.4%).

[0082] In some embodiments, the carbon-coated lithium iron phosphate material includes carbon-coated LiFePO4 and carbon-coated LiFe 1- y Ti y / 2 PO4, carbon-coated LiFe 1-x V x / 2 One or more of PO4, wherein x is 0.0005 to 0.013 and y is 0.0006 to 0.014. In some embodiments, the carbon-coated lithium iron phosphate material includes carbon-coated LiFePO4, carbon-coated LiFe... 0.992 Ti 0.004 PO4, carbon-coated LiFe 0.994 V 0.003 One or more of PO4. In some embodiments, the positive electrode active material may also include positive electrode active materials known in the art for lithium-ion batteries. The positive electrode active material may include at least one of the following materials: lithium phosphate, lithium transition metal oxide, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium phosphate include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4, also referred to as LFP), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (such as LiNi). 1 / 3 Co1 / 3 Mn 1 / 3 O2, also known as NCM 333 LiNi 0.5 Co 0.2 Mn 0.3 O2, also known as NCM 523 LiNi 0.5 Co 0.25 Mn 0.25 O2, also known as NCM 211 LiNi 0.6 Co 0.2 Mn 0.2 O2, also known as NCM 622 LiNi 0.8 Co 0.1 Mn 0.1 O2, also known as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.05 Al 0.05 At least one of O2 and its modified compounds. Modified compounds refer to substances obtained by modification methods such as doping or coating based on the above-mentioned substances.

[0083] In the examples of positive electrode active materials in this application, the molar content of oxygen is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of oxygen will fluctuate.

[0084] In some embodiments, the positive electrode sheet has a coating areal density of 19.4–26.7 mg / cm³. 2 By adopting the aforementioned areal density, the high energy density requirements of individual battery cells can be met while maintaining their kinetic performance and ensuring their lifespan. Therefore, this areal density achieves a balance between energy density and performance. Energy storage batteries have high requirements for both energy density and lifespan. Using the aforementioned areal density, while achieving high energy density, it minimizes the risk of lithium-ion transport path elongation, thus maintaining the battery's kinetic performance and resulting in a battery with both high energy density and long lifespan.

[0085] In some embodiments, the coating surface density of the positive electrode sheet is 19.4–19.5 mg / cm³. 2 19.5~21.0mg / cm 2 21.0~22.1mg / cm 2 22.1~24.0mg / cm 2 24.0~26.6mg / cm 2Or 26.6~26.7mg / cm 2 .

[0086] The surface density of the positive electrode is the weight of the positive electrode material coated on a unit area of ​​current collector. The method for measuring the surface density of the positive electrode is as follows: Take a 2cm×2cm double-sided coated positive electrode and measure its weight, which is recorded as M0mg; then obtain a 2cm×2cm positive current collector by scraping off the positive electrode material layer and measure its weight, which is recorded as M1mg. Then the surface density of the positive electrode material layer is (M0-M1) / 2 / 4.

[0087] In some embodiments, the positive electrode material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0088] In some embodiments, the positive electrode material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0089] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0090] In some embodiments, the compaction density of the positive electrode material layer is 2.38–2.70 g / cm³. 3 Within the aforementioned range, the compaction density of the cathode material layer can meet the high energy density requirements of the battery cell while avoiding cracks or even breakage due to excessive elongation of the cathode current collector, which would affect manufacturing yield and battery cell reliability. Therefore, maintaining the compaction density of the cathode material layer within this range is beneficial for meeting the energy density, reliability, and manufacturability requirements of the battery cell.

[0091] In some embodiments, the compaction density of the positive electrode material layer is 2.38–2.40 g / cm³. 3 2.40~2.50g / cm 3 Or 2.50~2.70g / cm 3 .

[0092] The compaction density of the positive electrode material layer is the weight of the positive electrode active material per unit volume of positive electrode sheet. The test method is as follows:

[0093] Take a 2cm×2cm double-coated positive electrode sheet, measure its weight and record it as M0 mg, and measure its thickness and record it as T0 cm; then obtain a 2cm×2cm positive current collector by scraping off the positive electrode material layer, measure its weight and record it as M1 mg, and measure its thickness and record it as T1 cm; then the coating surface density of the positive electrode sheet = (M0-M1) / 2 / 4, the thickness of the positive electrode material layer = T0-T1; the compaction density of the positive electrode material layer = coating surface density of the positive electrode sheet / thickness of the positive electrode material layer.

[0094] [Electrolytes]

[0095] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0096] In some embodiments, the battery cell further includes an electrolyte comprising a solvent, the solvent comprising a cyclic carbonate.

[0097] In some embodiments, the electrolyte contains ethylene carbonate (EC), and in some embodiments, the mass of ethylene carbonate accounts for 15%-25% (e.g., 15%-18%, 18%-20%, or 20%-25%) of the electrolyte mass. Ethylene carbonate has a high dielectric constant and good lithium salt dissolution and electrolysis capabilities. Adding ethylene carbonate within the above-mentioned mass percentage range can, on the one hand, utilize its high dielectric constant and good lithium salt dissolution and electrolysis capabilities, and on the other hand, control the impact of excessive addition on electrolyte viscosity and conductivity, maintaining rapid lithium ion migration, avoiding increased battery polarization, and thus contributing to extended battery life.

[0098] In some embodiments, the electrolyte contains propylene carbonate (PC), and in some embodiments, the mass of propylene carbonate accounts for 1%-8% (e.g., 1%-2%, 2%-4%, 4%-5%, or 5%-8%) of the electrolyte mass. Propylene carbonate can improve the lithium salt dissociation capability. Adding propylene carbonate within the above-mentioned mass percentage range can, on the one hand, improve the lithium salt dissociation capability and lower the low-temperature freezing point of the electrolyte, thereby improving the low-temperature performance of the battery; on the other hand, it can make propylene carbonate compatible with graphite, so that after addition, it is less likely to be embedded in the graphite on the graphite side of the negative electrode along with lithium ions, reducing the possibility of graphite stripping and helping to maintain battery life.

[0099] In some embodiments, the electrolyte further includes solvents other than cyclic carbonates, including but not limited to one or more of chain carbonates, nitrile solvents, ketone solvents, and sulfone solvents, such as methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, tetrahydrofuran, ethylene glycol dimethyl ether, dioxolane, acetone, acetonitrile, and butyronitrile.

[0100] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0101] In some embodiments, the electrolyte may optionally include additives. As examples, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0102] [shell]

[0103] The battery cell of this application may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly for encapsulating the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0104] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations.

[0105] In some embodiments, the housing includes an end cap and a housing, the housing having an opening, and the end cap covering the opening. The housing may have one or more openings. The end cap may also have one or more.

[0106] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab or indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0107] In some embodiments, a pressure relief mechanism is provided on the casing. The pressure relief mechanism is used to release the internal gas of the battery cell.

[0108] As an example, the internal pressure or temperature of a battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell reaches the predetermined threshold, the pressure relief mechanism is activated or a weak structure in the pressure relief mechanism is broken, thereby creating an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the battery cell.

[0109] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0110] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0111] The term "actuation" as used in this application refers to the activation or actuation of the pressure relief mechanism to a certain state, thereby releasing the internal pressure and temperature of the battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is activated, the high-temperature, high-pressure substances inside the battery cell are discharged as waste from the activated portion. This method allows for pressure and temperature relief of the battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0112] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for venting gas inside the battery cell.

[0113] The emissions from battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of separators, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0114] [Isolation membrane]

[0115] In some embodiments, the secondary battery 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.

[0116] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can 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 can be the same or different, without particular limitation.

[0117] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0118] Figure 1 shows a square-structured battery cell 5 as an example.

[0119] In some embodiments, referring to FIG2, the housing may include a housing 51 and an end cap 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the end cap 53 can be closed by covering the opening. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0120] [Battery Device]

[0121] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0122] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0123] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0124] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0125] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0126] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0127] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0128] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0129] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0130] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0131] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0132] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0133] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0134] Figure 6 shows an example of an electrical device. This device 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 the individual battery cells, a battery pack or battery module can be used. [Example]

[0135] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0136] General testing methods:

[0137] Test the following parameters using the method described above:

[0138] In the negative electrode active material, the interlayer spacing D1 of the (002) crystal plane of amorphous carbon and the interlayer spacing D2 of the (002) crystal plane of graphite core; in the Raman spectrum of carbon-coated lithium iron phosphate material, the ratio of the peak intensity Id of the D peak to the peak intensity Ig of the G peak Id / Ig; the thickness t2 of the second negative electrode material layer and the thickness t1 of the first negative electrode material layer; the porosity of the second negative electrode material layer and the porosity of the first negative electrode material layer; the coating surface density of the positive electrode material layer; and the compaction density of the positive electrode material layer.

[0139] The cycle performance of individual battery cells was tested using the following method:

[0140] At 25℃, the battery cells were subjected to charge-discharge cycle tests on a charge-discharge tester with a cycle rate of 0.5P (i.e., both the charge and discharge rates are 0.5P). The charging voltage ranged from 2.5V to 3.65V. The capacity retention rate after the cycles was calculated. The capacity retention rate after the 25℃ cycle is: Capacity retention rate after the nth cycle = (Discharge capacity after the nth cycle / Discharge capacity in the first cycle) × 100%.

[0141] General preparation method:

[0142] Preparation of lithium iron phosphate materials

[0143] 0.1 mol lithium carbonate, 0.2 mol ferrous oxalate, 0.2 mol ammonium dihydrogen phosphate powder, and 0.015 mol glucose were uniformly dispersed in 50 ml of anhydrous ethanol and ball-milled at 400 rpm for 12 h. The ball-milled powder was then dried to obtain a mixed precursor powder. The precursor powder was then placed in a sintering furnace, an inert atmosphere was introduced, and the temperature was raised to 600 °C at a rate of 2 °C / min and held for 14 h to obtain carbon-coated lithium iron phosphate material.

[0144] 0.1 mol lithium carbonate, 0.1984 mol ferrous oxalate, 0.2 mol ammonium dihydrogen phosphate powder, 0.0008 mol tetrabutyl titanate, and 0.015 mol glucose were uniformly dispersed in 50 ml of anhydrous ethanol and ball-milled at 400 rpm for 12 h. The ball-milled powder was then dried to obtain a mixed precursor powder. The precursor powder was then placed in a sintering furnace, and an inert reducing atmosphere was introduced. The temperature was raised to 600 °C at a rate of 2 °C / min and held for 14 h to obtain carbon-coated titanium-doped lithium iron phosphate material.

[0145] 0.1 mol lithium carbonate, 0.1988 mol ferrous oxalate, 0.2 mol ammonium dihydrogen phosphate powder, 0.0006 mol ammonium metavanadate, and 0.015 mol glucose were uniformly dispersed in 50 ml of anhydrous ethanol and ball-milled at 400 rpm for 12 h. The ball-milled powder was then dried to obtain a mixed precursor powder. The precursor powder was then placed in a sintering furnace, and an inert reducing atmosphere was introduced. The temperature was raised to 600 °C at a rate of 2 °C / min and held for 14 h to obtain carbon-coated vanadium-doped lithium iron phosphate material.

[0146] Example 1

[0147] Preparation of the positive electrode sheet

[0148] Carbon-coated Ti-doped lithium iron phosphate material was used as the positive electrode active material and mixed with conductive agent Super P and binder polyvinylidene fluoride (PVDF) at a mass ratio of 97:1:2. N-methylpyrrolidone solvent was added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on both sides of the positive electrode current collector aluminum foil, and then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0149] Preparation of the negative electrode sheet

[0150] (1) The first active material (amorphous carbon-coated graphite, commercially available) is mixed with conductive agent Super-P, dispersant CMC and binder SBR in an appropriate amount of deionized water at a mass ratio of 96.4:0.4:1.0:2.2 to form a uniform negative electrode slurry A1.

[0151] (2) The second active material (amorphous carbon-coated graphite, commercially available) is mixed with conductive agent Super-P, dispersant CMC and binder SBR in an appropriate amount of deionized water at a mass ratio of 96.0:0.7:1.1:2.2 to form a uniform negative electrode slurry A2.

[0152] (3) The negative electrode paste A1 is coated on the negative electrode current collector copper foil, and the negative electrode paste A2 is coated on A1. After drying, cold pressing, electrode tab die cutting and slitting, a double-coated negative electrode sheet is obtained.

[0153] Preparation of Electrolyte

[0154] In an argon-filled glove box (water content <10ppm, oxygen content <1ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and propylene carbonate (PC) were mixed in a mass ratio of 20:75:5 to obtain an electrolyte solvent. Then, fully dried lithium salt LiPF6 was added to the above solvent and mixed to prepare an electrolyte with a lithium salt concentration of 1mol / L.

[0155]

Isolation Film

[0156] Polyethylene film is used as the separation membrane.

[0157] [Preparation of battery cells]

[0158] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes for isolation. After winding, a bare electrode assembly is obtained. Positive and negative tabs are then welded on to obtain the electrode assembly. The electrode assembly is then assembled into a casing, and the prepared electrolyte is injected. The battery is then encapsulated, allowed to stand, formed, shaped, and its capacity tested to finally produce a lithium-ion battery.

[0159] Compared with Example 3, Examples 12 and 13 changed t1, t2 and their ratio, while other conditions remained the same.

[0160] Table 3

[0161] As can be seen from Table 3, under the condition that other conditions are fixed, t2 / t1 satisfies 2 / 3≤t2 / t1≤1.5, and the battery has a good cycle life.

[0162] Compared with Example 3, Example 14 changed the porosity of the first active material layer and the porosity of the second active material layer, while other conditions remained the same.

[0163] Table 4

[0164] As can be seen from Table 4 and Example 3, under the condition that other conditions are fixed, the porosity of the second negative electrode material layer is greater than that of the first negative electrode material layer. That is, the tiered distribution design with sparse upper and dense lower pores is beneficial to accelerate the conduction speed of ions on the negative electrode surface, and ultimately improves the dynamics of the battery cell and enhances the cycle life.

[0165] Compared with Example 3, Examples 15-18 changed the content of ethylene carbonate or propylene carbonate in the electrolyte, while other conditions remained the same.

[0166] Table 5

[0167] As can be seen from Table 5, under the condition that other conditions are fixed, using an electrolyte containing 15%-25% ethylene carbonate and / or 1%-8% propylene carbonate can improve the lithium salt dissolution and electrolysis capabilities, which is beneficial to make the electrolyte have sufficient conductivity and improve the cycle life of the battery.

[0168] Compared with Example 3, Examples 19-22 changed the coating surface density of the positive electrode sheet and the compaction density of the positive electrode material layer, while other conditions remained the same.

[0169] Table 6

[0170] As shown in Table 6, under the condition that other factors remain constant, the coating surface density of the positive electrode sheet is 19.5–26.6 mg / cm³. 2 This can maintain the dynamic performance of the battery cells, which is beneficial to obtaining good battery cell life. The compaction density of the positive electrode material layer is 2.38–2.7 g / cm³. 3 It helps maintain the energy density and reliability of individual battery cells and improves the cycle life of the battery.

[0171] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, comprising an electrode assembly, the electrode assembly including a positive electrode, a negative electrode, and a separator; the negative electrode including a negative current collector and a negative electrode material layer disposed on at least one side of the negative current collector, the negative electrode material layer comprising a negative electrode active material, the negative electrode active material including amorphous carbon-coated graphite, the amorphous carbon-coated graphite comprising a graphite core and an amorphous carbon coating layer on the surface of the graphite core, wherein... The interlayer spacing of the (002) crystal plane of the amorphous carbon is D1, and the interlayer spacing of the (002) crystal plane of the graphite core is D2, wherein D1 and D2 satisfy a distance of 1.

0. <D1 / D2≤1.1; The positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one side of the positive current collector. The positive electrode material layer contains a positive electrode active material, which includes carbon-coated lithium iron phosphate material. In the Raman spectrum of the carbon-coated lithium iron phosphate material, the ratio of the peak intensity Id of the D peak to the peak intensity Ig of the G peak satisfies Id / Ig≤1.

5.

2. The battery cell according to claim 1, wherein, In the Raman spectrum of the carbon-coated lithium iron phosphate material, the ratio of the peak intensity Id of the D peak to the peak intensity Ig of the G peak satisfies 0.9 ≤ Id / Ig ≤ 1.

3.

3. The battery cell according to claim 1 or 2, wherein, The negative electrode material layer includes a first negative electrode material layer and a second negative electrode material layer. The first negative electrode material layer is disposed on at least one side of the negative electrode current collector, and the second negative electrode material layer is disposed on the side of the first negative electrode material layer away from the negative electrode current collector. The ratio of the thickness t2 of the second negative electrode material layer to the thickness t1 of the first negative electrode material layer satisfies 2 / 3 ≤ t2 / t1 ≤ 1.5; and / or the porosity of the second negative electrode material layer is greater than the porosity of the first negative electrode material layer.

4. The battery cell according to any one of claims 1-3, wherein, The thickness t1 of the first negative electrode material layer and the thickness t2 of the second negative electrode material layer are each independently selected from 57 μm to 87 μm; and / or, the porosity of the first negative electrode material layer and the porosity of the second negative electrode material layer are each independently selected from 25% to 36%.

5. The battery cell according to any one of claims 1-4, wherein, The lithium iron phosphate material contains one or more doping elements selected from Ti, V, Mg, Zr, and Y.

6. The battery cell according to any one of claims 1-5, wherein, In the positive electrode sheet, the coating surface density is 19.4–26.7 mg / cm³. 2 .

7. The battery cell according to any one of claims 1-6, wherein, The compaction density of the positive electrode material layer is 2.38–2.70 g / cm³. 3 .

8. The battery cell according to any one of claims 1-7, wherein, The battery cell also includes an electrolyte, which includes a solvent, and the solvent includes cyclic carbonates.

9. The battery cell according to claim 8, wherein, The solvent includes ethylene carbonate (EC), and optionally, the ethylene carbonate accounts for 15%-25% of the mass of the electrolyte.

10. The battery cell according to claim 8 or 9, wherein, The solvent includes propylene carbonate (PC), and optionally, the mass of the propylene carbonate accounts for 1%-8% of the mass of the electrolyte.

11. A battery device comprising a plurality of battery cells according to any one of claims 1-10.

12. An energy storage device comprising a plurality of battery cells according to any one of claims 1-10 or a plurality of battery devices according to claim 11, wherein the battery cells or the battery devices are used to store or provide electrical energy.

13. An energy storage system comprising a power conversion device and an energy storage device according to claim 12, wherein the power conversion device is used to electrically connect a power generation device and the energy storage device.

14. An electrical device comprising a battery cell according to any one of claims 1-10, a battery device according to claim 11, an energy storage device according to claim 12, or an energy storage system according to claim 13, wherein the battery cell or the battery device is used to store or provide electrical energy.

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