Battery cell, battery device, power consuming device, and energy storage device

Abstract

The application provides a battery monomer, a battery device, a power consumption device and an energy storage device. The battery monomer is a soft package battery monomer, which comprises an electrode assembly and an electrolyte. The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator. The separator is located between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector. The negative electrode film layer comprises a negative electrode active material. The negative electrode active material comprises graphite. The graphitization degree of the graphite is 94% to 98%. In a full charge state, the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.23 g / cm 3 . The battery monomer has excellent energy density and cycle stability.

Description

Technical Field

[0001] The present application relates to the technical field of battery cells, and in particular to a battery cell, a battery device, an electrical device, and an energy storage device. Background Art

[0002] In recent years, battery cells have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] As the market demands for longer driving ranges for electric devices, higher requirements are being placed on the energy density of battery cells. However, while achieving improved energy density, this often leads to a deterioration in cycle stability, which has become a technical problem that urgently needs to be addressed in this field. Summary of the Invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell, a battery device, an electrical device and an energy storage device, wherein the battery cell has both excellent energy density and cycle life.

[0005] The first aspect of the present application provides a battery cell, which is a soft-pack battery cell, including an electrode assembly and an electrolyte, wherein the electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet; the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material, wherein the negative electrode active material includes graphite, wherein the graphitization degree of the graphite is 94% to 98%, and when the battery cell is fully charged, the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.23g / cm 3 .

[0006] The embodiments of the present application achieve comprehensive improvements in energy density and cycle life by using graphite with a graphitization degree within the above range and a negative electrode film layer with a compaction density within the above range in a soft-pack battery cell.

[0007] In any embodiment, the graphite has a degree of graphitization of 94% to 96%.

[0008] Graphite with a degree of graphitization within the above range enables the battery cell to have excellent energy density while further improving the cycle stability.

[0009] In any embodiment, when the battery cell is fully charged, the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.17g / cm 3 .

[0010] The battery cell with the compaction density of the negative electrode film layer within the above range has excellent energy density and further improved cycle stability.

[0011] In any embodiment, the single-side coating mass of the negative electrode film layer is 0.11 g / 1540.25 mm 2 Up to 0.16g / 1540.25mm 2 .

[0012] In any embodiment, the single-side coating mass of the negative electrode film layer is 0.12 g / 1540.25 mm 2 to 0.135g / 1540.25mm 2 .

[0013] The negative electrode film layer with a single-sided coating quality within the above range has a thin thickness and a low number of pores. Under the same injection coefficient, it is more conducive to improving the infiltration of the electrolyte into the pores of the film layer and increasing the content of free electrolyte. The proportion of electrolyte effectively participating in the reaction is higher, thereby further reducing the probability of lithium deposition on the negative electrode sheet due to insufficient electrolyte in the film layer, local loss of electrolyte in the late cycle, and subsequent deterioration of the cycle life. The cycle stability of the battery cell is further improved while having excellent energy density.

[0014] In any embodiment, the cold pressed density of the negative electrode film layer is 1.45 g / cm 3 Up to 1.6g / cm 3 .

[0015] The cold pressed density of the negative electrode film layer is within the above range, and the battery cell has both excellent energy density and cycle life.

[0016] In any embodiment, the negative electrode active material has a first charge gram capacity of 379 mAh / g to 385 mAh / g.

[0017] In any embodiment, the negative electrode active material has an initial discharge capacity of 345 mAh / g to 360 mAh / g.

[0018] The initial charge and discharge gram capacity of the negative electrode active material is within the above range, so that the battery cell has excellent energy density.

[0019] In any embodiment, the negative electrode active material has a Dv50 of 14 μm to 23 μm.

[0020] In any embodiment, the negative electrode active material has a Dv10 of 6 μm to 18 μm.

[0021] In any embodiment, the negative electrode active material has a Dv90 of 17 μm to 49 μm.

[0022] In any embodiment, the negative electrode active material has a Dv99 of 40 μm to 50 μm.

[0023] In some embodiments, the specific surface area of ​​the negative electrode active material is 1.4 m 2 / g to 1.6m 2 / g.

[0024] The volume distribution particle size and specific surface area of ​​the negative electrode active material are within the above ranges, so that the negative electrode active material has both low reactivity and a short lithium ion solid phase migration path, and the battery cell has both excellent energy density and cycle life.

[0025] In any embodiment, the negative electrode film layer includes a first negative electrode film layer arranged on at least one side of the negative electrode current collector and a second negative electrode film layer arranged on the side of the first negative electrode film layer away from the negative electrode current collector, and the mass proportion of the binder in the first negative electrode film layer is greater than the mass proportion of the binder in the second negative electrode film layer.

[0026] The negative electrode slurry used in high-energy-density battery cells often contains a high content of active material. When applied to the surface of the current collector, it is prone to powder loss and separation from the current collector after drying. In addition, during the drying and solvent removal step of the aqueous negative electrode slurry, the binder tends to float up as the solvent evaporates, resulting in insufficient binder content in the lower film layer and a significant deterioration in the cohesion between the active material particles and the adhesion between the active material particles and the copper foil substrate. In the embodiment of the present application, the mass proportion of the binder in the first negative electrode film layer is greater than the mass proportion of the binder in the second negative electrode film layer. This helps to improve the adhesion between the negative electrode film layer and the current collector, the cohesion of the negative electrode film layer, and restrain the expansion of the negative electrode active material, thereby further improving the cycle stability of the battery cell.

[0027] In any embodiment, based on the total mass of the first negative electrode film layer, the mass proportion of the binder is 1%-3%.

[0028] In any embodiment, based on the total mass of the first negative electrode film layer, the mass proportion of the binder is 1.5%-2.3%.

[0029] The mass proportion of the binder in the first negative electrode film layer is within the above range. The first negative electrode film layer takes into account the bonding force between the active material particles and the copper foil substrate and the cohesive force of the film layer. The battery cell has both excellent cycle life and energy density.

[0030] In any embodiment, based on the total mass of the second negative electrode film layer, the mass proportion of the binder is 0.3%-1.5%, and can be optionally 0.3%-0.8%.

[0031] The mass proportion of the binder in the second negative electrode film layer is within the above range, the second negative electrode film layer has both excellent cohesion and energy density, and the battery cell has both excellent cycle life and energy density.

[0032] In any embodiment, based on the total mass of the first negative electrode film layer, the mass proportion of graphite is 70%-97%.

[0033] In any embodiment, based on the total mass of the second negative electrode film layer, the mass proportion of graphite is 80%-98%.

[0034] The mass proportion of graphite in the first negative electrode film layer and the second negative electrode film layer is within the above range, and the battery cell has both excellent energy density and cycle life.

[0035] In any embodiment, the ratio of the thickness of the first negative electrode film layer to the thickness of the second negative electrode film layer is 3:7 to 6:4.

[0036] The high binder content in the first negative electrode film layer and the high graphite content in the second negative electrode film layer, combined with the first and second negative electrode film layers having a thickness ratio within the above range, are conducive to further improving the energy density and cycle stability of the battery cell while meeting the processing technology of the electrode.

[0037] In any embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. When the battery cell is fully charged, the compaction density of the positive electrode film layer is 2.35 g / cm 3 Up to 2.55g / cm 3 .

[0038] In any embodiment, the cold pressed density of the positive electrode film layer is 2.4 g / cm 3 Up to 2.6g / cm 3 .

[0039] The positive electrode film layer with a compaction density within the above range has both excellent liquid retention capacity and thin film thickness, so that the battery cell further has excellent energy density and cycle life.

[0040] In any embodiment, the single-sided coating mass of the positive electrode film layer is 0.26 g / 1540.25 mm 2 Up to 0.35g / 1540.25mm 2 .

[0041] The positive electrode film layer with a single-sided coating mass within the above range enables the battery cell to further have both excellent energy density and cycle life.

[0042] In any embodiment, the positive electrode film layer includes a positive electrode active material, wherein the positive electrode active material includes: an olivine-structured lithium-containing phosphate, and a carbon coating layer located on at least a portion of the surface of the lithium-containing phosphate.

[0043] The carbon coating layer is beneficial to improving the electronic conductivity of lithium-containing phosphates and improving the solid-phase transmission rate of electrons, thereby further improving the energy density and cycle performance of the battery cell.

[0044] In any embodiment, the lithium-containing phosphate comprises a component as shown in Formula I,

[0045] Li x A y Me a M b P 1-c X c Y z Formula I,

[0046] Among them, 0.5≤x≤1.3, 0≤y≤1.3, 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.4, 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes one or more of Na, K and Mg; Me includes one or more of Mn, Fe, Co and Ni; M includes one or more of Mn, Ti, Ba, Co, Mg, Al, Ni and Sn; X includes one or more of S, Si, Cl, B, C, N and P; Y includes one or more of O and F.

[0047] The lithium-containing phosphate with an olivine structure having the above components has good structural stability, and further improves the cycle stability of the battery cell.

[0048] In any embodiment, the positive electrode active material includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, lithium cobalt phosphate and modified forms of any of the foregoing substances, wherein the modified form includes one or more of doping modification and coating modification.

[0049] In any embodiment, the positive electrode active material has a first charge gram capacity of 150 mAh / g to 170 mAh / g.

[0050] In any embodiment, the positive electrode active material has an initial discharge capacity of 140 mAh / g to 165 mAh / g.

[0051] Positive electrode active materials with initial charge and discharge gram capacity within the above range are beneficial to further improving the energy density of battery cells.

[0052] In some embodiments, in a cumulative distribution curve of the number of particles obtained from a cross section of the positive electrode film along the thickness direction of the electrode sheet, the number distribution particle size D10 of the particles is 0.2 μm to 1.2 μm.

[0053] In any embodiment, in a cumulative distribution curve of the number of particles obtained from a cross section of the positive electrode film layer along the thickness direction of the electrode sheet, the number distribution particle size D50 of the particles is 0.8 μm to 2 μm.

[0054] In any embodiment, in a cumulative distribution curve of the number of particles obtained from a cross section of the positive electrode film along the thickness direction of the electrode sheet, the number distribution particle size D90 of the particles is 1 μm to 10 μm.

[0055] In any embodiment, in a cumulative distribution curve of the number of particles obtained from a cross section of the positive electrode film layer along the thickness direction of the electrode sheet, the number distribution particle size D99 of the particles is 8 μm to 20 μm.

[0056] In any embodiment, the specific surface area of ​​the positive electrode active material is 11 m 2 / g to 14m 2 / g.

[0057] The number distribution particle size and specific surface area of ​​the positive electrode active material are within the above range, so that the positive electrode active material has excellent particle grading, low reactivity and polarization effect, which is conducive to reducing the breakage of active material particles under the same compaction density and reducing the degree of side reactions between the electrolyte. The battery cell further takes into account excellent energy density and cycle life.

[0058] In any embodiment, the electrolyte includes a lithium salt, and the lithium salt includes one or more of lithium difluorophosphate LiPO2F2, lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium bis(oxalatoborate) LiBOB, and lithium perchlorate LiClO4.

[0059] In any embodiment, the lithium salt comprises lithium difluorophosphate LiPO2F2.

[0060] Adding the above-mentioned lithium salts to the electrolyte is beneficial to improving the stability of the negative electrode solid electrolyte interface film (SEI film), alleviating the repeated rupture and generation of the SEI film caused by the expansion of the negative electrode active material particles, thereby further improving the cycle life of the battery cell. Among them, lithium difluorophosphate LiPO2F2 has excellent effect in improving the cycle life of the battery cell, low cost and mildness, and is suitable for the industrial preparation of battery cells.

[0061] In any embodiment, the lithium salt further includes one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium hexafluoroarsenate (LiAsF6).

[0062] The above-mentioned lithium salts have high solubility and dissociation, which makes the electrolyte have excellent conductivity, provides a transmission channel for lithium ions, and enables the additive lithium salts to play a role in forming the SEI film, thereby further improving the cycle life of the battery cell.

[0063] In any embodiment, the concentration of the lithium salt in the electrolyte is 0.5 mol / L to 2 mol / L.

[0064] When the concentration of the lithium salt is within the above range, the electrolyte has both excellent ionic conductivity and wettability, thereby further improving the cycle stability of the battery cell of the embodiment of the present application.

[0065] In any embodiment, based on the total mass of the lithium salt, the mass proportion of lithium difluorophosphate LiPO2F2 is 2% to 30%.

[0066] In any embodiment, based on the total mass of the lithium salt, the mass proportion of lithium difluorophosphate LiPO2F2 is 5% to 15%.

[0067] Based on the total mass of lithium salt, the mass proportion of lithium difluorophosphate LiPO2F2 is within the above range. The battery cell has both an electrolyte with excellent electrical conductivity and a stable SEI film, thereby further improving the cycle life of the battery cell.

[0068] In any embodiment, the electrolyte further includes an additive, and the additive includes one or more of a carbonate additive and a sulfur-containing additive.

[0069] In any embodiment, the carbonate additive includes one or more of vinylene carbonate (VC) and fluorinated ethylene carbonate (FEC).

[0070] Carbonate additives can evolve into organic components in the SEI film, improving the toughness of the SEI film, thereby further improving the stability of the SEI film during the battery cell cycle, reducing side reactions between the electrolyte and the negative electrode film layer, and facilitating further improvement of the cycle life of the battery cell.

[0071] In any embodiment, the sulfur-containing additive includes one or more of vinyl sulfate, vinyl sulfite, propylene sulfate, vinyl methyl sulfate, vinyl methyl sulfite, vinyl ethylene sulfate, and sulfonate esters.

[0072] Sulfur-containing additives can evolve into sulfur-containing inorganic components in the SEI film, further improving the thermal stability of the SEI film at high temperatures, which is beneficial to further improve the cycle stability of the battery cell.

[0073] In any embodiment, the electrolyte further includes a solvent, the solvent includes a carbonate solvent, and the carbonate solvent includes one or more of chain carbonates, cyclic carbonates, and fluorinated carbonates.

[0074] In any embodiment, the linear carbonate includes one or more of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), and ethylmethyl carbonate (MEC).

[0075] In any embodiment, the cyclic carbonate includes one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinyl ethylene carbonate (VEC).

[0076] In any embodiment, the fluorinated carbonates include one or more of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

[0077] In any embodiment, the isolation film includes a base film, a first functional layer located on both sides of the base film, and a second functional layer located between the base film and at least one side of the first functional layer, the first functional layer includes polymer particles, and the second functional layer includes an inorganic substance.

[0078] The inorganic matter in the second functional layer can improve the wettability and heat resistance of the isolation membrane to the electrolyte. The polymer in the first functional layer can improve the processing performance and stability of the isolation membrane, and prevent the isolation membrane from moving in the battery cell and causing internal short circuit. The above isolation membrane can further improve the cycle stability and safety performance of the battery cell.

[0079] In any embodiment, the second functional layer is located between the base film and the first functional layer on the side close to the positive electrode plate, and the single layer thickness of the second functional layer is 1 μm-3 μm.

[0080] The impedance of the positive electrode active material is relatively large, and it generates more heat during the charging and discharging process. The second functional layer close to the positive electrode side helps to further reduce the thermal shrinkage of the separator. The positive electrode current collector aluminum foil is more likely to produce burrs during the die-cutting process. The second functional layer facing the positive electrode helps to improve the toughness and strength of the separator, preventing burrs from puncturing the separator and causing internal short circuits, thereby further improving the cycle stability and safety performance of the battery cell.

[0081] In any embodiment, the second functional layer is located between the base film and the first functional layer close to the negative electrode plate, and the single layer thickness of the second functional layer is 1 μm-3 μm.

[0082] In a lithium phosphate positive electrode active material system with lower heat generation, the second functional layer of the separator can also be placed close to the negative electrode side, which helps to improve the wetting effect of the separator on the negative electrode side on the electrolyte, thereby reducing the formation of lithium dendrites on the negative electrode side and helping to prevent lithium dendrites from piercing the separator, thereby further improving the cycle stability and safety performance of the battery cell.

[0083] In any embodiment, the second functional layer is located between the base film and the first functional layers on both sides, and the thickness of a single layer of the second functional layer is 1 μm-2 μm.

[0084] When the thickness of the second functional layer is within the above range, the isolation membrane has both excellent wettability and a short lithium ion diffusion distance, which is beneficial to further improve the cycle stability and energy density of the battery cell.

[0085] In any embodiment, the polymer particles include one or more of fluorine-containing polymer particles and non-fluorine-containing polymer particles; wherein the fluorine-containing polymer particles include one or more of vinylidene fluoride homopolymers and vinylidene fluoride copolymers, and the non-fluorine-containing polymer particles include acrylic copolymers.

[0086] In any embodiment, the inorganic material includes one or more of alumina monohydrate, aluminum oxide, silicon oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide.

[0087] In any embodiment, the filling coefficient of the battery cell is 1.8g / Ah-3g / Ah, and can be optionally 2.2g / Ah-2.7g / Ah.

[0088] Since the space utilization rate of soft-pack battery cells is higher, the injection coefficient is controlled within the above range, so that the injected electrolyte provides the battery cells with excellent cycle life while improving the weight energy density. It also alleviates the excessive SEI film impedance caused by excessive additives, which worsens the charging DCR, and reduces the effects of gas production caused by the reaction of electrolyte components and the subsequent bulging of the soft-pack shell with low mechanical strength, thereby improving the safety performance and usage stability of the battery cells.

[0089] A second aspect of the present application provides a battery device, comprising the battery cell provided in the first aspect of the present application, wherein the battery device comprises at least one of a battery module, a battery pack, and an energy storage battery.

[0090] The third aspect of the present application further provides an electrical device, which includes the battery device provided in the second aspect of the present application, and the battery device is used to provide electrical energy.

[0091] The fourth aspect of the present application further provides an energy storage device, which includes the battery device provided in the second aspect of the present application, and the battery device is used to store electrical energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0092] Figure 1 is a schematic diagram of a battery cell according to one embodiment of the present application;

[0093] Figure 2 yes Figure 1 A partial cross-sectional view of a battery cell according to an embodiment of the present application is shown;

[0094] Figure 3 FIG2 is a schematic diagram of an electrical device using a battery cell according to an embodiment of the present application as a power source.

[0095] Description of reference numerals:

[0096] 1. Electrode assembly; 2. Positive electrode tab; 3. Negative electrode tab; 4. Tab heat sealant; 5. Shell. DETAILED DESCRIPTION

[0097] Below, the embodiments of the battery cells, battery devices, electrical devices and energy storage devices of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0098] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0099] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0100] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0101] Unless otherwise specified, all steps of the present 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 may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0102] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0103] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0104] Graphite with a high degree of graphitization has a high specific capacity and, as a negative electrode active material, helps increase the energy density of battery cells. However, highly graphitized graphite undergoes a more significant volume change when lithium is released from the battery, which in turn increases the expansion force of the battery cells. This increases the compressive force on the positive and negative electrode sheets, squeezing out the electrolyte in the membrane layer, which in turn compromises the cycling stability of the battery cells. This problem is particularly pronounced in pouch cells with higher energy densities. Producing pouch cells that balance high energy density and cycle life is a pressing technical challenge in this field.

[0105] Based on this, the first aspect of the present application provides a battery cell, which is a soft-pack battery cell, including an electrode assembly and an electrolyte, the electrode assembly including a positive electrode sheet, a negative electrode sheet and a separator, the separator being located between the positive electrode sheet and the negative electrode sheet; the negative electrode sheet including a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector, the negative electrode film layer including a negative electrode active material, the negative electrode active material including graphite, the graphitization degree of the graphite being 94% to 98%, and the compaction density of the negative electrode film layer being 1.1 g / cm when the battery cell is fully charged. 3 to 1.23g / cm 3 .

[0106] Soft-pack battery cells have high space utilization, and the flexible shell material used is lighter and thinner than hard shell materials such as aluminum shells and steel shells, which is conducive to improving the energy density of battery cells. Graphite with a high degree of graphitization means that the carbon layers in the material are more regularly arranged and have fewer lattice defects, which is conducive to the insertion and extraction of lithium ions, reduces the migration resistance of electrons, and reduces the irreversible consumption of lithium ions, making it have excellent specific capacity, which is further conducive to improving the energy density of battery cells. However, since the interlayers of graphite with a high degree of graphitization are more tightly bonded, the volume expansion of graphite after lithium ions are embedded in the graphite interlayers is more significant, which can easily lead to the extrusion of electrolyte stored in the pore space inside the negative electrode film layer. The lack of electrolyte in the film layer hinders the transmission of lithium ions, which can easily cause the growth of lithium dendrites on the surface of the negative electrode plate, causing a decrease in the cycle life of the battery cell. In addition, the increase in thickness of the negative electrode film layer due to expansion will also squeeze the positive electrode film layer and the separator, which also has the problem of electrolyte extrusion, further detrimental to the cycle life of the battery cell. Moreover, due to the limited space for soft-pack battery cells to accommodate electrolytes and their easy swelling, the risk of swelling is easily caused when there is more electrolyte. Under the same capacity, the electrolyte in soft-pack battery cells is less than that in hard-shell batteries. This makes it more likely that there will be a lack of electrolyte in the membrane layer and difficulty in reabsorption after the electrolyte is squeezed out, which further leads to insufficient electrolyte infiltration in the membrane layer, seriously deteriorating the cycle life. The applicant found through research that the negative electrode film layer with a lower compaction density is more loosely stacked. The loose membrane structure can provide space for the volume change of high-graphitization graphite during lithium insertion and extraction, thereby reducing the probability of the electrolyte in the negative electrode film layer being squeezed out, and reducing the change in the thickness of the negative electrode film layer, thereby alleviating the squeezing of the positive electrode film layer and the separator, reducing the extrusion of the electrolyte in the positive electrode film layer and the separator, and the negative electrode film layer with a lower compaction density has a larger porosity, which is conducive to improving its ability to retain and reabsorb the electrolyte, further alleviating the problem of insufficient electrolyte in the negative electrode film layer, so that the cycle life of the battery cell is significantly improved. In summary, the embodiments of the present application achieve comprehensive improvements in energy density and cycle life by using graphite with a degree of graphitization within the above range and a negative electrode film layer with a compaction density within the above range in the soft-pack battery cell.

[0107] A soft-pack battery cell refers to a basic unit whose shell is made of flexible material and can realize the mutual conversion of chemical energy and electrical energy.

[0108] The term "degree of graphitization" refers to an indicator that measures the degree to which carbon atoms form a close-packed hexagonal graphite crystal structure.

[0109] In this application, the degree of graphitization of the graphite material can be tested using methods known in the art, such as using an X-ray diffractometer (e.g., a Bruker D8 Discover), with reference to JIS K0131-1996 and JB / T 4220-2011, to obtain the average interlayer spacing d002 of the (002) crystal plane in the crystal structure of the graphite material. The degree of graphitization can then be calculated using the formula g = (0.344 - d002) / (0.344 - 0.3354) × 100%. In the above formula, d002 is the average interlayer spacing of the (002) crystal plane in the crystal structure of the graphite material expressed in nanometers (nm). The negative electrode active material can be freshly prepared or scraped from the negative electrode film layer after disassembling the battery cell. For example, place the battery cell at 25°C, discharge the battery cell at a constant current of 0.33C to 2.0V, let it stand for 5 minutes, and then discharge it at a constant current of 0.04C to 2.0V, which is recorded as a full discharge state. Disassemble the battery cell to take out the negative electrode plate, dissolve the negative electrode plate, and centrifuge it at 3000r / min for more than 30 minutes to remove the binder in the film layer. Graphite will be deposited in the lower layer of the sediment, and the conductive agent will be on the upper layer of the sediment. Take the graphite in the lower layer for graphitization test.

[0110] Those skilled in the art can control the graphitization degree of graphite through any known process. As an example, using petroleum coke as raw material, heat treatment was performed at 2400°C-2800°C, with a gradient of 200°C, for 2 hours to obtain graphite materials with different degrees of graphitization. The graphite obtained at 2400°C had a graphitization degree of 83%, the graphite obtained at 2600°C had a graphitization degree of 88%, and the graphite obtained at 2800°C had a graphitization degree of 90%. In addition to controlling the treatment temperature, the raw materials used in the graphitization treatment, the treatment time, and other processes will all affect the graphitization degree of the product.

[0111] In some embodiments, the graphite may have a degree of graphitization of 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, or any range therebetween.

[0112] The compacted density of the negative electrode film layer in a fully charged battery cell is well known in the art and can be measured using methods known in the art. For example, a battery cell is charged at 25°C at a constant current of 0.33C to 3.65V, and then charged at a constant voltage of 3.65V to 0.05C. At this point, the battery cell is fully charged. The negative electrode sheet is then disassembled and the compacted density of the negative electrode film layer is measured. The compacted density of the negative electrode film layer is calculated as the single-sided coating mass of the negative electrode film layer divided by the single-sided thickness of the negative electrode film layer, as measured after disassembly.

[0113] In this application, “single-sided coating mass of the negative electrode film layer” refers to the mass of the negative electrode film layer per unit area on one side of the current collector.

[0114] In this application, the single-sided coating quality of the negative electrode film layer can be tested using methods known in the art. For example, the negative electrode sheet can be removed from a disassembled battery (if the negative electrode sheet is coated on both sides, the negative electrode film layer can be wiped off one side first), punched into small discs with an area of ​​S1, and the mass of each disc is measured and recorded as M1. The negative electrode film layer of the weighed negative electrode sheet is then wiped off, and the mass of the negative electrode current collector is weighed and recorded as M0. The single-sided coating quality of the positive electrode sheet = (M1 - M0) / S1.

[0115] The thickness of the negative electrode film layer is well known in the art and can be measured using methods known in the art, such as a micrometer (e.g., Mitutoyo 293-100, with an accuracy of 0.1 μm). It is understood that when a battery cell is fully charged, the compaction density of the negative electrode film layer will differ from the design compaction density of the battery cell. Due to actual operational influences, the compaction density of the negative electrode film layer when a battery cell is fully charged is often lower than the design cold-pressed compaction density of the battery cell.

[0116] In some embodiments, the compaction density of the negative electrode film layer can be 1.1 g / cm 3 , 1.11g / cm 3 , 1.12g / cm 3 , 1.13g / cm 3 , 1.14g / cm 3 , 1.15g / cm 3 , 1.16g / cm 3 , 1.17g / cm 3 , 1.18g / cm 3 , 1.19g / cm 3 , 1.2g / cm 3 , 1.21g / cm 3 , 1.22g / cm 3 , 1.23g / cm 3 or any range of values ​​between them.

[0117] In some embodiments, the graphite has a degree of graphitization of 94% to 96%.

[0118] Graphite with a degree of graphitization within the above range enables the battery cell to have excellent energy density while further improving the cycle stability.

[0119] In some embodiments, when the battery cell is fully charged, the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.17g / cm 3 .

[0120] The battery cell with the compaction density of the negative electrode film layer within the above range has excellent energy density and further improved cycle stability.

[0121] In some embodiments, the single-side coating mass of the negative electrode film layer is 0.11 g / 1540.25 mm 2 Up to 0.16g / 1540.25mm 2 .

[0122] In some embodiments, the single-sided coating mass of the negative electrode film layer is 0.12 g / 1540.25 mm 2 to 0.135g / 1540.25mm 2 .

[0123] In some embodiments, the single-side coating mass of the negative electrode film layer is 0.11 g / 1540.25 mm 2 , 0.12g / 1540.25mm 2 、0.13g / 1540.25mm 2 、0.14g / 1540.25mm 2 、0.15g / 1540.25mm 2 、0.16g / 1540.25mm 2 or any range of values ​​between them.

[0124] The negative electrode film layer with a single-sided coating quality within the above range has a thin thickness and a low number of pores. Under the same injection coefficient, it is more conducive to improving the infiltration of the electrolyte into the pores of the film layer and increasing the content of free electrolyte. The proportion of electrolyte effectively participating in the reaction is higher, thereby further reducing the probability of lithium deposition on the negative electrode sheet due to insufficient electrolyte in the film layer, local loss of electrolyte in the late cycle, and subsequent deterioration of the cycle life. The cycle stability of the battery cell is further improved while having excellent energy density.

[0125] In some embodiments, the cold pressed density of the negative electrode film layer is 1.45 g / cm 3 Up to 1.6g / cm 3 .

[0126] In some embodiments, the cold pressed density of the negative electrode film layer is 1.45 g / cm 3 , 1.48g / cm 3 , 1.51g / cm 3 、1.54g / cm 3 、1.57g / cm 3 , 1.6g / cm 3 or any range of values ​​between them.

[0127] The cold pressed density of the negative electrode film layer is within the above range, and the battery cell has both excellent energy density and cycle life.

[0128] In some embodiments, the first charge gram capacity of the negative electrode active material is 379 mAh / g to 385 mAh / g.

[0129] In this application, the initial charge-discharge gram capacity of the negative electrode active material can be tested using methods known in the art. For example, the negative electrode active material, conductive agent carbon black, and polyvinylidene fluoride (PVDF) are thoroughly stirred in an appropriate amount of NMP solvent at a mass ratio of 91.6:1.8:6.6 to form a uniform negative electrode slurry. The negative electrode slurry is evenly coated on the surface of the negative electrode current collector copper foil, dried, and cold-pressed. Next, a lithium metal sheet is used as the counter electrode, and a polypropylene (PP) film is used as the separator. An electrolyte is then injected. The electrolyte formulation used is as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 1:1:1 to form an organic solvent. LiPF6 is then dissolved in the organic solvent to prepare an electrolyte solution with a concentration of 1.0 mol / L. CR2430 button cells are assembled in an argon-protected glove box. At 25°C, charge at a 0.1C rate to an upper cutoff voltage of 3.8V, then charge at a constant voltage until the current is less than 0.05C. Record the initial charge capacity as Cn. After 30 minutes of rest, discharge at a 0.1C rate to a lower cutoff voltage of 2.0V. Record the initial discharge capacity as Cm. The initial charge capacity in grams of the negative electrode active material = initial charge capacity Cn / mass m of the negative electrode active material, and the initial discharge capacity in grams = initial discharge capacity Cm / mass m of the negative electrode active material. It is understood that the initial charge capacity in grams and the initial discharge capacity in grams of the negative electrode active material can also be obtained by disassembling the battery, obtaining the negative electrode sheet, and assembling it into a button cell according to the method described above, followed by testing.

[0130] In some embodiments, the first charge gram capacity of the negative electrode active material is 379 mAh / g, 380 mAh / g, 381 mAh / g, 382 mAh / g, 383 mAh / g, 384 mAh / g, 385 mAh / g, or any range therebetween.

[0131] In some embodiments, the first discharge capacity of the negative electrode active material is 345 mAh / g to 360 mAh / g.

[0132] In some embodiments, the first discharge capacity of the negative electrode active material is 345 mAh / g, 348 mAh / g, 351 mAh / g, 354 mAh / g, 357 mAh / g, 360 mAh / g, or any range therebetween.

[0133] The initial charge and discharge gram capacity of the negative electrode active material is within the above range, so that the battery cell has excellent energy density.

[0134] In some embodiments, the negative active material has a Dv50 of 14 μm to 23 μm.

[0135] "Dv10, Dv50, Dv90, and Dv99" are well-known in the art and represent the particle sizes corresponding to the 10%, 50%, 90%, and 99% cumulative volume distribution percentages, respectively. These can be measured using instruments and methods known in the art. For example, they can be conveniently measured using a laser particle size analyzer, as per GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK. The negative electrode active material can be freshly prepared or scraped from the negative electrode film layer after disassembly of the battery cell. For example, discharge the battery to 0% SOC, then disassemble and take out the negative electrode, scrape a certain amount of powder on the electrode with a blade, and then use deionized water to clean it repeatedly by shaking for 5 to 10 times. After drying, sinter it in a tube furnace at 400°C for 2 hours. After sintering, take an appropriate amount of the sample to be tested (the sample concentration can ensure 8%-12% shading), add deionized water, and ultrasonically disperse it to ensure that the sample is completely dispersed. Then, measure the sample according to GB / T19077-2016 / ISO 13320:2009 standard.

[0136] In some embodiments, the negative electrode active material has a Dv50 of 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 23 μm, or any range therebetween.

[0137] In some embodiments, the negative active material has a Dv10 of 6 μm to 18 μm.

[0138] In some embodiments, the negative electrode active material has a Dv10 of 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, or any range therebetween.

[0139] In some embodiments, the negative active material has a Dv90 of 17 μm to 49 μm.

[0140] In some embodiments, the Dv90 of the negative electrode active material is 17 μm, 21 μm, 25 μm, 29 μm, 33 μm, 37 μm, 41 μm, 45 μm, 49 μm, or any range therebetween.

[0141] In some embodiments, the negative active material has a Dv99 of 40 μm to 50 μm.

[0142] In some embodiments, the Dv99 of the negative electrode active material is 40 μm, 41 μm, 42 μm, 43 μm, 44 μm, 45 μm, 46 μm, 47 μm, 48 μm, 49 μm, 50 μm, or any range therebetween.

[0143] In some embodiments, the specific surface area of ​​the negative electrode active material is 1.4 m 2 / g to 1.6m 2 / g.

[0144] In this application, specific surface area has a meaning well known in the art and can be tested using methods known in the art. The determination method can refer to GB / T19587-2017, using the nitrogen adsorption specific surface area analysis test method and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using a Tri-Star 3020 specific surface area pore size analyzer from Micromeritics, USA.

[0145] In some embodiments, the specific surface area of ​​the negative electrode active material is 1.4 m 2 / g, 1.42m 2 / g, 1.44m 2 / g, 1.46m 2 / g, 1.48m 2 / g, 1.5m 2 / g, 1.52m 2 / g, 1.54m 2 / g, 1.56m 2 / g, 1.58m 2 / g, 1.6m 2 / g or any range of values ​​between them.

[0146] The volume distribution particle size and specific surface area of ​​the negative electrode active material are within the above ranges, so that the negative electrode active material has both low reactivity and a short lithium ion solid phase migration path, and the battery cell has both excellent energy density and cycle life.

[0147] In some embodiments, the negative electrode film layer includes a first negative electrode film layer disposed on at least one side of the negative electrode current collector and a second negative electrode film layer disposed on the side of the first negative electrode film layer away from the negative electrode current collector, and the mass proportion of the binder in the first negative electrode film layer is greater than the mass proportion of the binder in the second negative electrode film layer.

[0148] In some embodiments, 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).

[0149] The binder content in the different film layers of the negative electrode sheet can be tested using any method known in the art. For example, lay a clean copper foil flat on a tabletop and cut the negative electrode sheet to be tested into 20 cm x 10 cm pieces. Prepare a clean razor blade. Hold the sheet with your left hand while holding the blade with your right hand, setting the blade at a 45-degree angle to the sheet. Scrape the powder from the center of the sheet from left to right, with a length of 10 cm and a width of 5 cm. If the powder is scraped 10 times from the start of the scraping to the release of the copper foil, the first three scrapings are samples of the second film layer, and the last three scrapings are samples of the first film layer. Store the collected samples in a sealed bottle. Weigh 50 mg of the collected sample, place it in an alumina crucible, and shake it flat. The binder content in the sample is determined using a thermogravimetric analyzer (nitrogen atmosphere, flow rate 20 mL / min). Heat the sample from 25°C to 600°C at a rate of 10°C / min. The percentage of mass loss in different regions of the sample represents the binder content in each region.

[0150] The negative electrode slurry used in high-energy-density battery cells often contains a high content of active material. When applied to the surface of the current collector, it is prone to powder loss and separation from the current collector after drying. In addition, during the drying and solvent removal step of the aqueous negative electrode slurry, the binder tends to float up as the solvent evaporates, resulting in insufficient binder content in the lower film layer and a significant deterioration in the cohesion between the active material particles and the adhesion between the active material particles and the copper foil substrate. In the embodiment of the present application, the mass proportion of the binder in the first negative electrode film layer is greater than the mass proportion of the binder in the second negative electrode film layer. This helps to improve the adhesion between the negative electrode film layer and the current collector, the cohesion of the negative electrode film layer, and restrain the expansion of the negative electrode active material, thereby further improving the cycle stability of the battery cell.

[0151] In some embodiments, based on the total mass of the first negative electrode film layer, the mass proportion of the binder is 1%-3%.

[0152] In some embodiments, based on the total mass of the first negative electrode film layer, the mass proportion of the binder is 1.5%-2.3%.

[0153] In some embodiments, based on the total mass of the first negative electrode film layer, the mass proportion of the binder is 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3% or any numerical range therebetween.

[0154] The mass proportion of the binder in the first negative electrode film layer is within the above range. The first negative electrode film layer takes into account the bonding force between the active material particles and the copper foil substrate and the cohesive force of the film layer. The battery cell has both excellent cycle life and energy density.

[0155] In some embodiments, based on the total mass of the second negative electrode film layer, the mass proportion of the binder is 0.3%-1.5%, and can be optionally 0.3%-0.8%.

[0156] In some embodiments, based on the total mass of the second negative electrode film layer, the mass proportion of the binder can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or any numerical range therebetween.

[0157] The mass proportion of the binder in the second negative electrode film layer is within the above range, the second negative electrode film layer has both excellent cohesion and energy density, and the battery cell has both excellent cycle life and energy density.

[0158] In some embodiments, based on the total mass of the first negative electrode film layer, the mass proportion of graphite is 70%-97%.

[0159] In some embodiments, based on the total mass of the first negative electrode film layer, the mass proportion of graphite is 70%, 73%, 76%, 79%, 82%, 85%, 88%, 91%, 94%, 97% or any numerical range therebetween.

[0160] In some embodiments, based on the total mass of the second negative electrode film layer, the mass proportion of graphite is 80%-98%.

[0161] In some embodiments, based on the total mass of the second negative electrode film layer, the mass proportion of graphite is 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98% or any numerical range therebetween.

[0162] The mass proportion of graphite in the first negative electrode film layer and the second negative electrode film layer is within the above range, and the battery cell has both excellent energy density and cycle life.

[0163] In some embodiments, the ratio of the thickness of the first negative electrode film layer to the thickness of the second negative electrode film layer is 3:7 to 6:4.

[0164] In some embodiments, the ratio of the thickness of the first negative electrode film layer to the thickness of the second negative electrode film layer is 3:7, 4:6, 5:5, 6:4, or any ratio range therebetween.

[0165] The high binder content in the first negative electrode film layer and the high graphite content in the second negative electrode film layer, combined with the first and second negative electrode film layers having a thickness ratio within the above range, are conducive to further improving the energy density and cycle stability of the battery cell while meeting the processing technology of the electrode.

[0166] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0167] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector. When the battery cell is fully charged, the compaction density of the positive electrode film layer is 2.35 g / cm 3 Up to 2.55g / cm 3 .

[0168] The compaction density of the positive electrode film layer can be tested by a method similar to the compaction density of the negative electrode film layer described above.

[0169] In some embodiments, when the battery cell is fully charged, the compaction density of the positive electrode film layer is 2.35 g / cm 3 , 2.37g / cm 3 , 2.39g / cm 3 , 2.41g / cm 3 , 2.43g / cm 3 , 2.45g / cm 3 , 2.47g / cm 3 , 2.49g / cm 3 , 2.51g / cm 3 , 2.53g / cm 3 , 2.55g / cm 3 or any range of values ​​between them.

[0170] In some embodiments, the cold pressed density of the positive electrode film layer is 2.4 g / cm 3 Up to 2.6g / cm 3 .

[0171] In some embodiments, the cold pressed density of the positive electrode film layer is 2.4 g / cm 3 , 2.42g / cm 3 , 2.44g / cm 3 , 2.46g / cm 3 , 2.48g / cm 3 , 2.5g / cm 3 , 2.52g / cm 3 , 2.54g / cm 3, 2.56g / cm 3 , 2.58g / cm 3 , 2.6g / cm 3 or any range of values ​​between them.

[0172] The positive electrode film layer with a compaction density within the above range has both excellent liquid retention capacity and thin film thickness, so that the battery cell further has excellent energy density and cycle life.

[0173] In some embodiments, the single-sided coating mass of the positive electrode film layer is 0.26 g / 1540.25 mm 2 Up to 0.35g / 1540.25mm 2 .

[0174] In some embodiments, the single-sided coating mass of the positive electrode film layer is 0.26 g / 1540.25 mm 2 , 0.27g / 1540.25mm 2 、0.28g / 1540.25mm 2 , 0.29g / 1540.25mm 2 、0.30g / 1540.25mm 2 、0.31g / 1540.25mm 2 、0.32g / 1540.25mm 2 、0.33g / 1540.25mm 2 、0.34g / 1540.25mm 2 , 0.35g / 1540.25mm 2 or any range of values ​​between them.

[0175] The positive electrode film layer with a single-sided coating mass within the above range enables the battery cell to further have both excellent energy density and cycle life.

[0176] In some embodiments, the positive electrode film layer includes a positive electrode active material, wherein the positive electrode active material includes: an olivine-structured lithium-containing phosphate, and a carbon coating layer located on at least a portion of the surface of the lithium-containing phosphate.

[0177] Olivine-structured lithium-containing phosphates are active materials with an olivine structure that include lithium ions and phosphate groups. The type of positive electrode active material can be determined by any method known in the art. For example, phase analysis methods such as X-ray diffraction (XRD) can be combined with elemental analysis methods such as energy dispersive spectroscopy and XPS.

[0178] The carbon coating layer is beneficial to improving the electronic conductivity of lithium-containing phosphates and improving the solid-phase transmission rate of electrons, thereby further improving the energy density and cycle performance of the battery cell.

[0179] In some embodiments, the lithium-containing phosphate includes a component as shown in Formula I,

[0180] Li x A y Me a M b P 1-c X c Y z Formula I,

[0181] Among them, 0.5≤x≤1.3, 0≤y≤1.3, 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.4, 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes one or more of Na, K and Mg; Me includes one or more of Mn, Fe, Co and Ni; M includes one or more of Mn, Ti, Ba, Co, Mg, Al, Ni and Sn; X includes one or more of S, Si, Cl, B, C, N and P; Y includes one or more of O and F.

[0182] In some embodiments, x can be selected as 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3 or any range therebetween, y can be selected as 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3 or any range therebetween, x+y can be selected as 0.9, 1, 1.1, 1.2, 1.3 or any range therebetween, a can be selected as 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5 or any range therebetween, b can be selected as 0, 0.1, 0.2, 0.3, 0.4, 0.5 or any numerical range therebetween, a+b can be selected as 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5 or any numerical range therebetween, c can be selected as 0, 0.1, 0.2, 0.3, 0.4, 0.5 or any numerical range therebetween, z can be selected as 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5 or any numerical range therebetween.

[0183] The lithium-containing phosphate with an olivine structure having the above components has good structural stability, and further improves the cycle stability of the battery cell.

[0184] In some embodiments, the positive electrode active material includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, lithium cobalt phosphate, and modified forms of any of the foregoing substances, wherein the modified form includes one or more of doping modification and coating modification.

[0185] In some embodiments, the positive electrode active material has a first charge gram capacity of 150 mAh / g to 170 mAh / g.

[0186] In this application, the positive electrode active material is assembled into a button cell and the electrical performance is tested on a blue battery tester. At 25±5°C in the voltage range of 2.0V~3.8V, after charging to 3.8V at a constant current of 1 / 3C, pause for 5 minutes, charge at a constant voltage to a cutoff current of 50μA, and then discharge to 2.0V at a constant current of 1C. The first charge capacity of the button cell is divided by the mass of the positive electrode active material as the first charge gram capacity of the positive electrode active material. The first discharge capacity of the button cell is divided by the mass of the positive electrode active material as the first discharge gram capacity of the positive electrode active material.

[0187] The preparation and testing process of button cells is as follows: 2.0g of positive electrode active material, conductive carbon black, and PVDF are mixed in a mass ratio of 0.9:0.05:0.05, and then organic solvent NMP (N-methylpyrrolidone) is added. After thorough mixing, the mixture is coated with a 150μm scraper and dried at 100℃ for 2h. The compacted density is 2.0g / cm 3 -2.2g / cm 3 The positive electrode was cold-pressed and punched into a 14 mm diameter disc using a hole punch. The discs were then weighed and the weight recorded. The weighed positive electrode was placed in a vacuum drying oven (105°C, 1-12 hrs, -90 kPa). After drying, the positive electrode was placed in a glove box. The battery was assembled in the order of negative electrode shell-nickel mesh-lithium sheet-diaphragm-positive electrode sheet-positive electrode shell. 65-87 μL (pipette) of electrolyte (the electrolyte was a mixed solvent of EC (ethylene carbonate) and DMC (1,2-dimethyl carbonate) with a volume ratio of 1:1, and the electrolyte was LiPF6) was added dropwise. The negative electrode was placed on top and placed in the groove of the sealing machine with a sealing pressure of 650 kg / cm 2 , remove the button battery with insulated tweezers, place it in a dust-free bag, remove the glove box, and place it in a constant temperature room for 3 hours to obtain the button battery for testing. It can be understood that the first charge gram capacity and first discharge gram capacity of the positive electrode active material can also be obtained by disassembling the battery, obtaining the positive electrode sheet, and assembling it into a button battery according to the method described above, and then testing.

[0188] In some embodiments, the first charge gram capacity of the positive electrode active material is 150 mAh / g, 152 mAh / g, 154 mAh / g, 156 mAh / g, 158 mAh / g, 160 mAh / g, 162 mAh / g, 164 mAh / g, 166 mAh / g, 168 mAh / g, 170 mAh / g, or any range therebetween.

[0189] In some embodiments, the positive electrode active material has a first discharge capacity of 140 mAh / g to 165 mAh / g.

[0190] In some embodiments, the first discharge gram capacity of the positive electrode active material is 140 mAh / g, 145 mAh / g, 150 mAh / g, 155 mAh / g, 160 mAh / g, 165 mAh / g, or any range therebetween.

[0191] Positive electrode active materials with initial charge and discharge gram capacity within the above range are beneficial to further improving the energy density of battery cells.

[0192] In some embodiments, in a cumulative distribution curve of the number of particles obtained from a cross section of the positive electrode film along the thickness direction of the electrode sheet, the number distribution particle size D10 of the particles is 0.2 μm to 1.2 μm.

[0193] In this application, the term "particle" refers to particles with identifiable complete boundaries in the field of view of the positive electrode film layer under a certain magnification, such as 10,000 times. Defects and scratches may exist inside the particles, but complete boundaries sufficient to separate the particles cannot be identified inside the particles.

[0194] In the cumulative distribution curve of the number of particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the number distribution particle size of the particles can be determined by methods known in the art. As an example, the battery cell is disassembled, the positive electrode sheet is taken out, and the cross-section of the electrode sheet is subjected to SEM testing (such as ZEISS electron microscope, magnification 10000X), and the size of all particles on a SEM image is counted. Software or manual statistics can be used, and the longest diameter of the particle is used as the particle size of the particle. The longest diameter of the particle refers to the maximum value of the distance between any two points on the outer edge line of the particle. Arrange the particle sizes from small to large, and take the particle sizes corresponding to 10%, 50%, 90%, and 99% of the cumulative distribution as the particle sizes D10, D50, D90, and D99 of the positive electrode active material particles in the particle size distribution curve of the cross section along the thickness direction of the positive electrode film layer; repeat the above operation many times, and after statistics are taken for multiple different areas (for example, 10) of the same electrode piece, take the average value as the particle size D10, D50, D90, and D99 of the particles in the cumulative distribution curve of the particles obtained in the cross section along the thickness direction of the positive electrode film layer of the sample to be tested.

[0195] During the compaction process, the positive electrode film layer is compacted in the thickness direction. Therefore, the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet can better reflect the actual compaction condition of the particles inside the film layer on a spatial scale compared to the surface of the positive electrode film layer.

[0196] It is understandable that in the prior art, a laser particle size analyzer is usually used to count the particle size of the positive electrode active material through the Malvern laser diffraction method. However, the applicant's research shows that because particles with small particle sizes are easy to agglomerate, the test results obtained by the Malvern laser diffraction method based on the laser scattering principle often measure the particle size of the particle agglomerates, which cannot truly reflect the particle size of the particles in the positive electrode active material, let alone the dispersion state of the positive electrode active material in the film layer, because the positive electrode active material in the film layer will be more dispersed during the pulping and film rolling process. The test results obtained by the Malvern laser diffraction method are affected by the particle size, specific surface area, and degree of agglomeration of the positive electrode active material. Compared with the actual dispersion in the electrode, the number of large particles obtained by the test is lower than the actual value, and the number of small particles is higher than the actual value. Therefore, the particle size obtained by the Malvern laser diffraction method test cannot be equivalent to or analogous to the particle size obtained by statistics in the embodiments of the present application.

[0197] In some embodiments, D10 is 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, or any range therebetween.

[0198] In some embodiments, in a cumulative distribution curve of the number of particles obtained from a cross section of the positive electrode film along the thickness direction of the electrode piece, the number distribution particle size D50 of the particles is 0.8 μm to 2 μm.

[0199] In some embodiments, D50 is 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, or any range therebetween.

[0200] In some embodiments, in a cumulative distribution curve of the number of particles obtained from a cross section of the positive electrode film along the thickness direction of the electrode sheet, the number distribution particle size D90 of the particles is 1 μm to 10 μm.

[0201] In some embodiments, D90 is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any range therebetween.

[0202] In some embodiments, in a cumulative distribution curve of the number of particles obtained from a cross section of the positive electrode film along the thickness direction of the electrode sheet, the number distribution particle size D99 of the particles is 8 μm to 20 μm.

[0203] In some embodiments, D99 is 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, or any range therebetween.

[0204] In some embodiments, the specific surface area of ​​the positive electrode active material is 11 m 2 / g to 14m 2 / g.

[0205] In some embodiments, the specific surface area of ​​the positive electrode active material is 11 m 2 / g, 11.5m 2 / g、12m 2 / g, 12.5m 2 / g、13m 2 / g, 13.5m 2 / g、14m 2 / g or any range of values ​​between them.

[0206] The number distribution particle size and specific surface area of ​​the positive electrode active material are within the above range, so that the positive electrode active material has excellent particle grading, low reactivity and polarization effect, which is conducive to reducing the breakage of active material particles under the same compaction density and reducing the degree of side reactions between the electrolyte. The battery cell further takes into account excellent energy density and cycle life.

[0207] In some embodiments, the positive electrode film layer may further optionally include a binder. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0208] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0209] In some embodiments, the electrolyte includes a lithium salt, and the lithium salt includes one or more of lithium difluorophosphate LiPO2F2, lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium bis(oxalatoborate) LiBOB, and lithium perchlorate LiClO4.

[0210] In some embodiments, the lithium salt includes lithium difluorophosphate, LiPO 2 F 2 .

[0211] The type and quality of the lithium salt in the electrolyte can be obtained by detecting the electrolyte by methods known to those skilled in the art. In the embodiments of the present application, a newly prepared electrolyte can be taken as a sample, the free electrolyte of a fresh battery can be taken as a sample, or a battery cell that has been fully discharged (discharged to the discharge cut-off voltage so that the charged state of the battery cell is about 0% SOC) can be reversely disassembled, and the free electrolyte obtained from the battery cell is used as a sample, and ion chromatography analysis is used for detection. The type and content of the organic components in the electrolyte are well known in the art and can be detected by equipment and methods known in the art. For example, the organic components of the electrolyte can be qualitatively and quantitatively analyzed by gas chromatography with reference to GB / T9722-2023 "General Rules for Gas Chromatography of Chemical Reagents". The types and contents of inorganic components / lithium salts in the electrolyte are well known in the art and can be detected using equipment and methods known in the art. For example, the inorganic components / lithium salts in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography analysis method with reference to standard JY / T020-2002 "General Rules for Ion Chromatography Analysis Methods".

[0212] Adding the above-mentioned lithium salts to the electrolyte is beneficial to improving the stability of the negative electrode solid electrolyte interface film (SEI film), alleviating the repeated rupture and generation of the SEI film caused by the expansion of the negative electrode active material particles, thereby further improving the cycle life of the battery cell. Among them, lithium difluorophosphate LiPO2F2 has excellent effect in improving the cycle life of the battery cell, low cost and mildness, and is suitable for the industrial preparation of battery cells.

[0213] In some embodiments, the lithium salt further includes one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium hexafluoroarsenate (LiAsF6).

[0214] The above-mentioned lithium salts have high solubility and dissociation, which makes the electrolyte have excellent conductivity, provides a transmission channel for lithium ions, and enables the additive lithium salt to play a role in forming the SEI film, thereby further improving the cycle life of the battery cell.

[0215] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.5 mol / L to 2 mol / L.

[0216] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2 mol / L or any range therebetween.

[0217] When the concentration of the lithium salt is within the above range, the electrolyte has both excellent ionic conductivity and wettability, thereby further improving the cycle stability of the battery cell of the embodiment of the present application.

[0218] In some embodiments, the mass of lithium difluorophosphate LiPO2F2 accounts for 2% to 30% based on the total mass of the lithium salt.

[0219] In some embodiments, the mass of lithium difluorophosphate LiPO2F2 accounts for 5% to 15% based on the total mass of the lithium salt.

[0220] It should be noted that since the lithium difluorophosphate in the electrolyte will be consumed during the formation and charge-discharge cycles to generate related components in the SEI film, after disassembling the battery cell to obtain the electrolyte, when testing the lithium difluorophosphate content by gas chromatography, the content may be 0%.

[0221] Specifically, taking the case where the mass content of lithium difluorophosphate is 0% as an example, this could be because lithium difluorophosphate is not added to the freshly prepared electrolyte, or because the electrolyte obtained after disassembling the battery cell does not contain lithium difluorophosphate. In this case, it is possible that lithium difluorophosphate was not added to the freshly prepared electrolyte, or it could be that a small amount of lithium difluorophosphate was added but participated in the SEI film formation reaction during the battery cell formation process, resulting in a mass content of lithium difluorophosphate of 0% during the test. Alternatively, the freshly prepared electrolyte includes lithium difluorophosphate.

[0222] Furthermore, regarding the addition of certain substances, such as additives, to the electrolyte, the content of additives in the battery cell electrolyte is related to the formation process, different battery life cycles, or different battery storage conditions due to the additives' role in film formation on the surface of the active material. Therefore, the additive content in a freshly prepared electrolyte may differ from that in an electrolyte obtained by reverse disassembling a battery cell. However, those skilled in the art can determine the approximate content range of the relevant substances in the fresh electrolyte based on the performance level of the battery cell (such as the number of cycles) and residual content. Similarly, those skilled in the art can also determine the approximate content range of the corresponding non-freshly prepared (i.e., after reverse disassembly) electrolyte based on the content of the freshly prepared additives, the performance requirements for the battery cell, the storage environment, etc.

[0223] Therefore, the lithium difluorophosphate content mentioned in the technical solution of the present application can be the content of lithium difluorophosphate actively added to the fresh electrolyte, or it can be the content of residual lithium difluorophosphate detected by reverse detection based on the actual battery status.

[0224] It is understood that in some embodiments, the lithium difluorophosphate added to the electrolyte is completely converted into inorganic components in the SEI film during the formation process. In some embodiments, residual lithium difluorophosphate remains in the electrolyte, which strengthens the SEI film during subsequent battery cell cycles.

[0225] In some embodiments, based on the total mass of the lithium salt, the mass proportion of lithium difluorophosphate LiPO2F2 is 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30% or any numerical range therebetween.

[0226] Based on the total mass of lithium salt, the mass proportion of lithium difluorophosphate LiPO2F2 is within the above range. The battery cell has both an electrolyte with excellent electrical conductivity and a stable SEI film, thereby further improving the cycle life of the battery cell.

[0227] In some embodiments, the electrolyte further includes an additive, and the additive includes one or more of a carbonate additive and a sulfur-containing additive.

[0228] Additives refer to components with low content in the electrolyte, which generally account for no more than 10% of the mass of the electrolyte. They are highly targeted and used in small amounts, and can significantly optimize the performance of a certain aspect of the battery without changing the production process.

[0229] In the present application, carbonate additives refer to compounds including carbonate groups (—O—CO—O—) and their derivatives, as well as mixtures containing the above compounds and their derivatives.

[0230] The type of additive in the electrolyte can be determined by testing the electrolyte using methods known to those skilled in the art. For example, the type and quality of the lithium salt in the electrolyte can be determined using the aforementioned testing method.

[0231] In some embodiments, the carbonate additive includes one or more of vinylene carbonate (VC) and fluorinated ethylene carbonate (FEC).

[0232] Carbonate additives can evolve into organic components in the SEI film, improving the toughness of the SEI film, thereby further improving the stability of the SEI film during the battery cell cycle, reducing side reactions between the electrolyte and the negative electrode film layer, and facilitating further improvement of the cycle life of the battery cell.

[0233] In some embodiments, the sulfur-containing additive includes one or more of vinyl sulfate, vinyl sulfite, propylene sulfate, vinyl methyl sulfate, vinyl methyl sulfite, vinyl ethylene sulfate, and sulfonate.

[0234] Sulfur-containing additives can evolve into sulfur-containing inorganic components in the SEI film, further improving the thermal stability of the SEI film at high temperatures, which is beneficial to further improve the cycle stability of the battery cell.

[0235] In some embodiments, the electrolyte further includes a solvent, the solvent includes a carbonate solvent, and the carbonate solvent includes one or more of chain carbonates, cyclic carbonates, and fluorinated carbonates.

[0236] As used herein, "cyclic carbonate" refers to a compound containing a carbonate group and a cyclic structure in its molecular structure.

[0237] As used herein, "linear carbonate" refers to a compound that contains carbonate groups in its molecular structure but does not form a cyclic structure.

[0238] In some embodiments, the linear carbonate includes one or more of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), and ethylmethyl carbonate (MEC).

[0239] In some embodiments, the cyclic carbonate includes one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinyl ethylene carbonate (VEC).

[0240] In some embodiments, the fluorinated carbonates include one or more of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

[0241] In some embodiments, the isolation film includes a base film, a first functional layer located on both sides of the base film, and a second functional layer located between the base film and at least one side of the first functional layer, the first functional layer includes polymer particles, and the second functional layer includes an inorganic substance.

[0242] The inorganic matter in the second functional layer can improve the wettability and heat resistance of the isolation membrane to the electrolyte. The polymer in the first functional layer can improve the processing performance and stability of the isolation membrane, and prevent the isolation membrane from moving in the battery cell and causing internal short circuit. The above isolation membrane can further improve the cycle stability and safety performance of the battery cell.

[0243] In some embodiments, the second functional layer is located between the base film and the first functional layer on the side close to the positive electrode plate, and the single layer thickness of the second functional layer is 1 μm-3 μm.

[0244] In some embodiments, the single layer thickness of the second functional layer may be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or any range therebetween.

[0245] The impedance of the positive electrode active material is relatively large, and it generates more heat during the charging and discharging process. The second functional layer close to the positive electrode side helps to further reduce the thermal shrinkage of the separator. The positive electrode current collector aluminum foil is more likely to produce burrs during the die-cutting process. The second functional layer facing the positive electrode helps to improve the toughness and strength of the separator, preventing burrs from puncturing the separator and causing internal short circuits, thereby further improving the cycle stability and safety performance of the battery cell.

[0246] In some embodiments, the second functional layer is located between the base film and the first functional layer close to the negative electrode plate, and the single layer thickness of the second functional layer is 1 μm-3 μm.

[0247] In a lithium phosphate positive electrode active material system with lower heat generation, the second functional layer of the separator can also be placed close to the negative electrode side, which helps to improve the wetting effect of the separator on the negative electrode side on the electrolyte, thereby reducing the formation of lithium dendrites on the negative electrode side and helping to prevent lithium dendrites from piercing the separator, thereby further improving the cycle stability and safety performance of the battery cell.

[0248] In some embodiments, the second functional layer is located between the base film and the first functional layers on both sides, and the thickness of a single layer of the second functional layer is 1 μm-2 μm.

[0249] In some embodiments, the single layer thickness of the second functional layer may be 1 μm, 1.5 μm, 2 μm, or any range therebetween.

[0250] When the thickness of the second functional layer is within the above range, the isolation membrane has both excellent wettability and a short lithium ion diffusion distance, which is beneficial to further improve the cycle stability and energy density of the battery cell.

[0251] In some embodiments, the polymer particles include one or more of fluorine-containing polymer particles and non-fluorine-containing polymer particles. The fluorine-containing polymer particles include one or more of vinylidene fluoride homopolymers and vinylidene fluoride copolymers. The non-fluorine-containing polymer particles include acrylic copolymers.

[0252] In some embodiments, the inorganic material includes one or more of alumina monohydrate, aluminum oxide, silicon oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide.

[0253] In some embodiments, the filling coefficient of the battery cell is 1.8 g / Ah-3 g / Ah, and can be optionally 2.2 g / Ah-2.7 g / Ah.

[0254] The filling factor of a battery cell refers to the ratio of the mass of the electrolyte within the cell to the battery capacity. The filling factor of a battery cell can be measured using any method known in the art. For example, the mass of the electrolyte in a battery cell can be measured using the following method: Weigh the battery, and record the mass as M0. Disassemble the battery cell and pour out the free electrolyte. Remove the internal electrode assembly and separate the positive and negative electrode sheets, separators, and mechanical components. Soak and clean the positive and negative electrode sheets, separators, and mechanical components in dimethyl carbonate (DMC) for 24 to 48 hours, repeated three or more times. Place the positive and negative electrode sheets, separators, and mechanical components in a 100°C oven for at least 24 hours until completely dried. Weigh the dried positive and negative electrode sheets, separators, and mechanical components, and record the mass as M1. The mass of the electrolyte in the battery cell is thus calculated as (M0 - M1). The filling coefficient is calculated as (M0-M1) / rated capacity of the battery cell. The rated capacity is the nominal capacity of the battery, or the discharge capacity of the battery cell after charging to 3.65V at a charge rate of 0.33C, then charging to 0.05C at a constant voltage of 3.65V, letting it rest for 10 minutes, and then discharging to 2.0V at a discharge rate of 0.33C.

[0255] In some embodiments, the filling coefficient of the battery cell can be 1.8g / Ah, 1.9g / Ah, 2.0g / Ah, 2.1g / Ah, 2.2g / Ah, 2.3g / Ah, 2.4g / Ah, 2.5g / Ah, 2.6g / Ah, 2.7g / Ah, 2.8g / Ah, 2.9g / Ah, 3.0g / Ah or any range therebetween.

[0256] Since the space utilization rate of soft-pack battery cells is higher, the injection coefficient is controlled within the above range, so that the injected electrolyte provides the battery cells with excellent cycle life while improving the weight energy density. It also alleviates the excessive SEI film impedance caused by excessive additives, which worsens the charging DCR, and reduces the effects of gas production caused by the reaction of electrolyte components and the subsequent bulging of the soft-pack shell with low mechanical strength, thereby improving the safety performance and usage stability of the battery cells.

[0257] In some embodiments, the battery cell includes a shell, the shell is made of a soft-pack material, and the soft-pack material includes an aluminum-plastic film.

[0258] In some embodiments, the aluminum-plastic film includes a composite film formed by aluminum and one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), nylon, polyethylene terephthalate (PET), and polyethylene (PE).

[0259] The second aspect of the present application provides a battery device, comprising the battery cell provided in the first aspect of the present application. In addition, the third aspect of the present application further provides an electric device, which comprises the battery device provided in the second aspect of the present application. The battery cell, battery module or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0260] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0261] Figure 3 This is an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the battery cells in this device, a battery pack or battery module can be used.

[0262] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0263] An embodiment of the present application also provides an energy storage device that uses a battery as a power source. The energy storage device may be, but is not limited to, an energy storage container, an energy storage cabinet, an energy storage power station, an energy storage battery pack, or a portable energy storage system.

[0264] Example

[0265] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0266] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0267] Example 1

[0268] (1) Preparation of negative electrode sheet

[0269] The negative electrode active material graphite, conductive agent (SP), thickener (CMC), and binder (SBR) were fully stirred and mixed in an appropriate amount of solvent deionized water in a mass ratio of 96.4:0.7:1.1:18 to obtain a negative electrode slurry, wherein the graphitization degree of the graphite was 96%, the first charge gram capacity was 380mAh / g, the first discharge gram capacity was 350mAh / g, the Dv50 was 15μm, and the specific surface area was 1.43m 2 / g, Dv10 is 8μm, Dv90 is 22.4μm; Dv99 is 42μm.

[0270] The negative electrode slurry is evenly coated on the negative electrode current collector copper foil, dried and cold pressed to obtain the negative electrode sheet. The thickness of the copper foil is 6 μm, and the cold pressed density of the negative electrode film is 1.52 g / cm 3 , single-sided coating mass is 0.1425g / 1540.25mm 2 .

[0271] (2) Preparation of positive electrode

[0272] The positive electrode active material lithium iron phosphate, the binder polyvinylidene fluoride, and the conductive agent (SP) were mixed in a mass ratio of 97:2:1, and then the solvent N-methylpyrrolidone (NMP) was added and stirred to form a positive electrode slurry. The positive electrode active material had an initial charge capacity of 160 mAh / g, an initial discharge capacity of 157 mAh / g, a Dv50 of 1.4 μm, and a specific surface area of ​​13.1 m 2 / g, Dv10 is 0.6μm, Dv90 is 5μm; Dv99 is 8.9μm. The positive electrode active material includes lithium iron phosphate and a carbon coating layer located on at least part of the surface of the lithium iron phosphate. The lithium iron phosphate includes the doping element Ti and has the general formula LiFe 0.85 Ti 0.15 PO4.

[0273] The positive electrode slurry is evenly coated on aluminum foil, dried and cold pressed to obtain the positive electrode sheet. The thickness of the aluminum foil is 15μm, and the cold pressed density of the positive electrode film is 2.6g / cm 3 , single-sided coating mass is 0.31g / 1540.25mm 2 .

[0274] (3) Preparation of isolation membrane

[0275] A polyethylene with a thickness of 7 μm is used as the base film. A 1 μm thick alumina monohydrate ceramic material is sprayed on the single side of the base film close to the positive electrode. On this basis, 1.85 mg / 1540.25 mm thick is sprayed on both sides. 2PVDF to obtain a composite isolation membrane.

[0276] (4) Preparation of electrolyte

[0277] In an argon-filled glove box (water content <1ppm, oxygen content <1ppm), EC (ethylene carbonate), DEC (diethyl carbonate), VC (vinylene carbonate), and DTD (vinyl sulfate) in a mass ratio of 38:45:0.5:0.2 were mixed, and fully dried lithium salt was added to obtain an electrolyte with a lithium salt concentration of 1 mol / L, wherein the lithium salt included LiPF6 (lithium hexafluorophosphate).

[0278] (5) Preparation of battery cells

[0279] A stacking machine is used to stack the positive electrode sheets, negative electrode sheets and separators in order, so that the separators are placed between the positive electrode sheets and the negative electrode sheets to act as a separator, thereby obtaining a stacked electrode assembly. The stacked cells are glued to tightly wrap the cells, and the glued stacked electrode assembly is placed in an outer package, which is a soft-pack aluminum-plastic film. The aluminum-plastic film is composed of an inner layer of polypropylene, a middle layer of aluminum foil, and an outer layer of nylon. Among them, the aluminum-plastic film outer package is obtained by a punching and trimming machine to obtain the target shape and size. The aluminum-plastic film is then heat-sealed, vacuum-baked, left to stand, and the electrolyte is injected and packaged. The soft-pack battery is then hot-pressed and cold-pressed, and finally the battery cell is obtained after processes such as formation, vacuum exhaust, and trimming. The injection coefficient of the battery cell is 2.4g / Ah, the width of the battery cell is 395mm, the height is 125mm, and the thickness is 42mm. When the battery cell is fully charged, the compaction density of the negative electrode film layer is 1.17g / cm 3 The compaction density of the positive electrode film is 2.5g / cm 3 .

[0280] Example 2-3

[0281] The preparation method of Example 2-3 is basically the same as that of Example 1, except that the graphitization degree of graphite is changed, as shown in Table 1.

[0282] Examples 4-5

[0283] The preparation method of Example 4-5 is basically the same as that of Example 1, except that the compaction density of the negative electrode film layer is changed, as shown in Table 1.

[0284] Examples 6-9

[0285] The preparation methods of Examples 6-9 are basically the same as those of Example 1, except that the coating mass on one side of the negative electrode film layer is changed, and the coating mass on one side of the positive electrode film layer changes accordingly, as shown in Table 1.

[0286] Example 10

[0287] The preparation method of Example 10 is basically the same as that of Example 1, except that the preparation of the negative electrode sheet is changed, as follows:

[0288] The negative electrode active material graphite, conductive agent (SP), thickener (CMC), and binder (SBR) are fully stirred and mixed in an appropriate amount of solvent deionized water at a mass ratio of 96.1:0.4:1.5:2 to obtain a first negative electrode slurry;

[0289] The negative electrode active material graphite, conductive agent (SP), thickener (CMC), and binder (SBR) are fully stirred and mixed in an appropriate amount of solvent deionized water at a mass ratio of 97.7:0.7:1.1:0.5 to obtain a second negative electrode slurry;

[0290] The first negative electrode slurry is evenly coated on the negative electrode collector copper foil; the second negative electrode slurry is coated on the surface of the first negative electrode slurry, and after drying and cold pressing, a negative electrode plate is obtained. The negative electrode plate includes a negative electrode collector and a negative electrode film layer on the negative electrode collector. The negative electrode film layer includes a first negative electrode film layer arranged on the surface of the negative electrode collector and a second negative electrode film layer arranged on the side of the first negative electrode film layer away from the negative electrode collector. The thickness ratio of the first negative electrode film layer to the second negative electrode film layer is 6:4.

[0291] Example 11

[0292] The preparation method of Example 11 is basically the same as that of Example 1, except that the compaction density of the positive electrode film layer is changed, as shown in Table 1.

[0293] Examples 12-13

[0294] The preparation methods of Examples 12-13 are basically the same as those of Example 1, except that the composition of the lithium salt is changed, as shown in Table 1.

[0295] Example 14

[0296] The preparation method of Example 14 is basically the same as that of Example 10, except that the composition of the lithium salt is changed, as shown in Table 1.

[0297] Examples 15-16

[0298] The preparation methods of Examples 15-16 are basically the same as those of Example 1, except that the injection coefficient is changed, as shown in Table 1.

[0299] Comparative Example 1-2

[0300] The preparation method of Comparative Example 1-2 is basically the same as that of Example 1, except that the graphitization degree of the graphite is changed, and the single-sided coating quality of the positive electrode film layer changes accordingly, as shown in Table 1.

[0301] Comparative Examples 3-4

[0302] The preparation method of Comparative Examples 3-4 is basically the same as that of Example 1, except that the compaction density of the negative electrode film layer is changed, as shown in Table 1.

[0303] Test Method

[0304] 1. Cycle life test

[0305] At 25°C, charge the lithium-ion battery at a constant current of 0.5C until the voltage reaches the rated voltage of 3.65V, then switch to constant voltage charging until the current drops to 0.05C. After standing for 5 minutes, discharge the lithium-ion battery at a constant current of 0.33C. When the voltage drops to 2.0V, cut off the charge and record the discharge capacity Qc. Perform a charge and discharge cycle test using this process, and record the discharge capacity Qn of each cycle. The life of the battery cell is the number of cycles when Qn / Qc=70%.

[0306] 2. Energy density test

[0307] The battery cell is charged at 2C constant current to a rated voltage of 3.65V at 25°C, and then charged to 0.02C at a constant voltage, then left for 30 minutes, and then discharged to 2V at 0.33C and left for 10 minutes. The volume of the lithium-ion battery = length × width × thickness, in units of L; the energy density of the battery is calculated using the discharge capacity, voltage, and volume of the battery. The energy of the battery = ∫UI×dt, where U is voltage (V), I is current (A), dt is time (s), and the unit of energy is Wh. Then, energy density = energy / volume.

[0308] Test results

[0309] Table 1

[0310]

[0311] According to the comparison between the embodiment of the present application and the comparative example, the battery cell is a soft-pack battery cell, the graphitization degree of the graphite is 94% to 98%, and the compaction density of the negative electrode film layer of the battery cell is 1.1g / cm 3 to 1.23g / cm 3 , the battery cells have both excellent energy density and cycle stability.

[0312] From the comparison between Examples 1 and 2 and Example 3, it can be seen that the graphitization degree of the graphite is 94% to 96%. While the battery cell has excellent energy density, the cycle stability is further improved.

[0313] From the comparison between Examples 1, 4 and 5, it can be seen that the compaction density of the negative electrode film layer is 1.1 g / cm3 to 1.17g / cm 3 While the battery cells have excellent energy density, the cycle stability is further improved.

[0314] From Examples 1, 6-9, it can be seen that the single-side coating mass of the negative electrode film layer is 0.11 g / 1540.25 mm 2 Up to 0.16g / 1540.25mm 2 The battery cell has both excellent energy density and cycle stability. The single-sided coating mass of the negative electrode film is 0.12g / 1540.25mm 2 to 0.135g / 1540.25mm 2 , the battery cells have both excellent energy density and cycle stability.

[0315] From the comparison between Example 10 and Example 1, it can be seen that the mass proportion of the binder in the first negative electrode film layer is greater than the mass proportion of the binder in the second negative electrode film layer, and the energy density and cycle stability of the battery cell are further improved.

[0316] As can be seen from Examples 1 and 11, the compacted density of the positive electrode film is 2.35 g / cm 3 Up to 2.55g / cm 3 , the battery cells have both excellent energy density and cycle stability.

[0317] Comparison of Examples 12 and 13 with Example 1 shows that the inclusion of one or more of lithium difluorophosphate (LiPO2F2), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalatoborate) (LiBOB), and lithium perchlorate (LiClO4) in the lithium salt helps improve the cycling stability of the battery cell. Comparison of Examples 12 and 13 shows that the inclusion of LiPO2F2 in the lithium salt further improves the cycling stability of the battery cell.

[0318] It can be seen from Examples 1, 15, and 16 that the filling coefficient of the battery cell is 2.2 g / Ah-2.7 g / A, and the battery cell has excellent volume energy density, weight energy density, cycle stability, and safety performance.

[0319] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A battery cell, characterized in that: The battery cell is a soft-pack battery cell, comprising an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet; The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material. The negative electrode active material includes graphite. The graphitization degree of the graphite is 94% to 98%. When the battery cell is fully charged, the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.17g / cm 3 .

2. The battery cell according to claim 1, wherein: The graphite has a degree of graphitization of 94% to 96%.

3. The battery cell according to claim 1, wherein: The single-sided coating mass of the negative electrode film layer is 0.11 g / 1540.25 mm 2 Up to 0.16g / 1540.25mm 2 .

4. The battery cell according to claim 1, wherein: The single-sided coating mass of the negative electrode film layer is 0.12 g / 1540.25 mm 2 to 0.135g / 1540.25mm 2 .

5. The battery cell according to claim 1, characterized in that The cold pressed density of the negative electrode film layer is 1.45 g / cm 3 Up to 1.6g / cm 3 .

6. The battery cell according to claim 1, characterized in that The negative electrode active material satisfies at least one of the following conditions: (1) The first charge capacity of the negative electrode active material is 379 mAh / g to 385 mAh / g; (2) The first discharge capacity of the negative electrode active material is 345 mAh / g to 360 mAh / g; (3) The Dv50 of the negative electrode active material is 14 μm to 23 μm; (4) The specific surface area of ​​the negative electrode active material is 1.4 m 2 / g to 1.6m 2 / g; (5) The Dv10 of the negative electrode active material is 6 μm to 18 μm; (6) The Dv90 of the negative electrode active material is 17 μm to 49 μm; (7) The Dv99 of the negative electrode active material is 40 μm to 50 μm.

7. The battery cell according to claim 1, characterized in that The negative electrode film layer includes a first negative electrode film layer arranged on at least one side of the negative electrode current collector and a second negative electrode film layer arranged on the side of the first negative electrode film layer away from the negative electrode current collector, and the mass proportion of the binder in the first negative electrode film layer is greater than the mass proportion of the binder in the second negative electrode film layer.

8. The battery cell according to claim 7, characterized in that Based on the total mass of the first negative electrode film layer, the mass proportion of the binder is 1%-3%.

9. The battery cell according to claim 7, characterized in that: Based on the total mass of the first negative electrode film layer, the mass proportion of the binder is 1.5%-2.3%.

10. The battery cell according to claim 7, characterized in that Based on the total mass of the second negative electrode film layer, the mass proportion of the binder is 0.3%-1.5%.

11. The battery cell according to claim 7, characterized in that Based on the total mass of the second negative electrode film layer, the mass proportion of the binder is 0.3%-0.8%.

12. The battery cell according to claim 7, characterized in that Based on the total mass of the first negative electrode film layer, the mass proportion of the graphite is 70%-97%; and / or, Based on the total mass of the second negative electrode film layer, the mass proportion of the graphite is 80%-98%.

13. The battery cell according to claim 7, characterized in that The ratio of the thickness of the first negative electrode film layer to the thickness of the second negative electrode film layer is 3:7 to 6:

4.

14. The battery cell according to claim 1, characterized in that The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. When the battery cell is fully charged, the compaction density of the positive electrode film layer is 2.35 g / cm 3 Up to 2.55g / cm 3 .

15. The battery cell according to claim 14, characterized in that The cold pressed density of the positive electrode film layer is 2.4 g / cm 3 Up to 2.6g / cm 3 .

16. The battery cell according to claim 14, characterized in that The single-sided coating mass of the positive electrode film layer is 0.26g / 1540.25mm 2 Up to 0.35g / 1540.25mm 2 .

17. The battery cell according to claim 14, characterized in that The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes: A lithium-containing phosphate with an olivine structure, and a carbon coating layer located on at least a portion of the surface of the lithium-containing phosphate.

18. The battery cell according to claim 17, characterized in that The lithium-containing phosphate includes a component as shown in Formula I, Li x A y Me a M b P 1-c X c Y z Formula I Among them, 0.5≤x≤1.3, 0≤y≤1.3, 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.4, 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes one or more of Na, K and Mg; Me includes one or more of Mn, Fe, Co and Ni; M includes one or more of Mn, Ti, Ba, Co, Mg, Al, Ni and Sn; X includes one or more of S, Si, Cl, B, C, N and P; Y includes one or more of O and F.

19. The battery cell according to claim 17, characterized in that The positive electrode active material includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, lithium cobalt phosphate and modified forms of any of the foregoing substances, wherein the modified form includes one or more of doping modification and coating modification.

20. The battery cell according to claim 17, wherein: The positive electrode active material satisfies at least one of the following conditions: (1) The first charge capacity of the positive electrode active material is 150 mAh / g to 170 mAh / g; (2) The positive electrode active material has an initial discharge capacity of 140 mAh / g to 165 mAh / g; (3) In the cumulative distribution curve of the number of particles obtained from the cross section of the positive electrode film along the thickness direction of the electrode sheet, the number distribution particle size D10 of the particles is 0.2 μm to 1.2 μm; (4) In the cumulative distribution curve of the number of particles obtained from the cross section of the positive electrode film along the thickness direction of the electrode sheet, the number distribution particle size D50 of the particles is 0.8 μm to 2 μm; (5) In the cumulative distribution curve of the number of particles obtained from the cross section of the positive electrode film along the thickness direction of the electrode sheet, the number distribution particle size D90 of the particles is 1 μm to 10 μm; (6) In the cumulative distribution curve of the number of particles obtained from the cross section of the positive electrode film along the thickness direction of the electrode sheet, the particle size distribution D99 of the particles is 8 μm to 20 μm; (7) The specific surface area of ​​the positive electrode active material is 11m 2 / g to 14m 2 / g.

21. The battery cell according to claim 1, characterized in that The electrolyte includes a lithium salt, and the lithium salt includes one or more of lithium difluorophosphate LiPO2F2, lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium bis(oxalatoborate) LiBOB, and lithium perchlorate LiClO4.

22. The battery cell according to claim 21, characterized in that The lithium salt includes lithium difluorophosphate LiPO2F2.

23. The battery cell according to claim 21, characterized in that The lithium salt further includes one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium hexafluoroarsenate (LiAsF6).

24. The battery cell according to claim 21, characterized in that The concentration of the lithium salt in the electrolyte is 0.5 mol / L to 2 mol / L.

25. The battery cell according to claim 22, characterized in that Based on the total mass of the lithium salt, the mass proportion of lithium difluorophosphate LiPO2F2 is 2% to 30%.

26. The battery cell according to claim 22, characterized in that Based on the total mass of the lithium salt, the mass proportion of lithium difluorophosphate LiPO2F2 is 5% to 15%.

27. The battery cell according to claim 1, characterized in that The electrolyte further includes additives, and the additives include one or more of carbonate additives and sulfur-containing additives.

28. The battery cell according to claim 27, characterized in that The carbonate additive includes one or more of vinylene carbonate (VC) and fluorinated ethylene carbonate (FEC); and / or, The sulfur-containing additive includes one or more of vinyl sulfate, vinyl sulfite, propylene sulfate, vinyl methyl sulfate, vinyl methyl sulfite, vinyl ethylene sulfate, and sulfonic acid ester.

29. The battery cell according to claim 1, characterized in that The electrolyte further includes a solvent, and the solvent includes a carbonate solvent, and the carbonate solvent includes one or more of chain carbonates, cyclic carbonates, and fluorinated carbonates.

30. The battery cell according to claim 29, characterized in that The chain carbonate includes one or more of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), and ethylmethyl carbonate (MEC); The cyclic carbonate includes one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinyl ethylene carbonate (VEC); and / or, The fluorinated carbonates include one or more of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

31. The battery cell according to claim 1, characterized in that The isolation film includes a base film, a first functional layer located on both sides of the base film, and a second functional layer located between the base film and the first functional layer on at least one side, the first functional layer includes polymer particles, and the second functional layer includes inorganic matter.

32. The battery cell according to claim 31, characterized in that The second functional layer is located between the base film and the first functional layer close to the positive electrode plate, and the single layer thickness of the second functional layer is 1 μm-3 μm.

33. The battery cell according to claim 31, characterized in that The second functional layer is located between the base film and the first functional layer close to the negative electrode plate, and the single layer thickness of the second functional layer is 1 μm-3 μm.

34. The battery cell according to claim 31, characterized in that The second functional layer is located between the base film and the first functional layers on both sides, and the thickness of a single layer of the second functional layer is 1 μm-2 μm.

35. The battery cell according to claim 31, characterized in that The polymer particles include one or more of fluorine-containing polymer particles and non-fluorine polymer particles; The fluorine-containing polymer particles include one or more of vinylidene fluoride homopolymers and vinylidene fluoride copolymers, and the non-fluorine polymer particles include acrylic acid ester copolymers.

36. The battery cell according to claim 31, characterized in that The inorganic substance includes one or more of monohydrated aluminum oxide, aluminum oxide, silicon oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide and tin oxide.

37. The battery cell according to claim 1, characterized in that The liquid filling coefficient of the battery cell is 1.8g / Ah-3g / Ah.

38. The battery cell according to claim 1, characterized in that The liquid filling coefficient of the battery cell is 2.2g / Ah-2.7g / Ah.

39. A battery device, characterized in that: A battery cell comprising the battery cell according to any one of claims 1 to 38.

40. An electrical device, characterized in that: The battery device according to claim 39 is used to provide electrical energy.

41. An energy storage device, characterized in that: The battery device according to claim 39 is used to store electrical energy.

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