Battery cell and preparation method thereof, secondary battery and power utilization device

Abstract

The invention provides a battery cell, a preparation method of the battery cell, a secondary battery and a power utilization device. The preparation method of the battery cell comprises the following steps: providing positive electrode slurry and coating to prepare a positive electrode plate; the compaction density of the positive pole piece is 2.4 to 2.8 g / cc; providing negative electrode slurry and coating to prepare a negative electrode plate; wherein the compaction density of the negative pole piece is 1.4 to 1.7 g / cc; assembling the positive pole piece, the negative pole piece and a diaphragm to prepare a battery cell; forming the battery cell for 3-30 minutes by adopting the current of 0.1-1 C; forming for 60 to 180 minutes by adopting a current of 1.5 to 4 C to finish the formation; and carrying out capacity grading and offline on the formed battery cell. The method is simple and easy to implement and low in cost, and the gain effects of high-temperature storage, first effect and cycle performance of the battery cell are obtained. The invention further provides that the battery cell has good comprehensive performance. Finally, the invention further provides a secondary battery and an electric device, and the high-temperature storage performance, the cycle performance, the first effect and the rate capability of the secondary battery are comprehensively good.

Description

Technical Field

[0001] The present application relates to the field of secondary batteries, and in particular to a battery cell and a preparation method thereof, a secondary battery, and an electrical device. Background Art

[0002] With the continuous development of society and science and technology, lithium-ion batteries have been widely used in electronic products, electric vehicles, power stations and other fields. However, in some application scenarios, lithium-ion batteries will be placed at high temperatures for a long time, which requires lithium-ion batteries to have good high-temperature storage performance. At present, placing lithium-ion batteries at high temperatures will cause the loss of high-temperature storage capacity of lithium-ion batteries. The main reason is the loss of active lithium ions caused by side reactions on the anode surface. In related technologies, increasing the density or thickening of the SEI film can reduce the activity of side reactions on the anode surface, reduce the loss of active lithium ions, and improve high-temperature storage. However, it will also bring about problems such as reduced first efficiency, poor rate, and poor cycle performance. Summary of the invention

[0003] The present application aims to solve one of the technical problems in the related art at least to some extent.

[0004] On the one hand, the present application proposes a method for preparing a battery cell, which increases the compaction density of the positive electrode sheet to improve the energy density; at the same time, reduces the compaction density of the negative electrode sheet, which can improve the SEI film formation quality, improve the first efficiency, rate, high-temperature storage and cycle performance; and when the battery cell is formed, a small current is used to form a dense SEI film, which comprehensively improves the high-temperature storage performance of the battery cell.

[0005] On the other hand, the present application proposes a battery cell, and the battery cell obtained by the preparation method provided by the present application has good comprehensive performance.

[0006] On the other hand, the present application proposes a secondary battery, which applies battery cells with good comprehensive performance to the secondary battery, reduces the side reactions between the negative electrode and the electrolyte, is beneficial to improving the high-temperature storage of the secondary battery, and improves the defects of reduced first efficiency and poor rate.

[0007] The last aspect of the present application proposes an electrical device, in which a battery cell with good comprehensive performance is applied to a secondary battery, and the obtained secondary battery is assembled and applied to the electrical device to expand the temperature application range of the electrical device.

[0008] According to the embodiment of the first aspect of the present application, a method for preparing a battery cell is proposed, comprising the following steps:

[0009] Providing a positive electrode slurry and applying it to prepare a positive electrode sheet; wherein the compaction density of the positive electrode sheet is 2.4-2.8 g / cc;

[0010] Providing a negative electrode slurry and applying it to prepare a negative electrode sheet; wherein the compaction density of the negative electrode sheet is 1.4-1.7 g / cc;

[0011] The positive electrode sheet and the negative electrode sheet are assembled with a separator to prepare a battery cell; the battery cell is firstly charged with a current of 0.1-1C for 3-30 minutes; and then charged with a current of 1.5-4C for 60-180 minutes to complete the charging;

[0012] The cells after formation are divided into different capacities and taken off the production line.

[0013] In some embodiments, the positive electrode slurry includes a positive electrode active material, a positive electrode conductor and a positive electrode binder;

[0014] And / or, the mass ratio of the positive electrode active material, the positive electrode conductive agent and the positive electrode binder is (96-98): (0.5-1.5): (1.5-3.5);

[0015] And / or, the positive electrode active material includes lithium iron phosphate.

[0016] In some embodiments, the coating surface density of the positive electrode slurry is 2-8 g / m 2 .

[0017] In some embodiments, the negative electrode active slurry includes a negative electrode active material, a negative electrode conductive agent and a negative electrode binder;

[0018] And / or, the mass ratio of the negative electrode active material, the negative electrode conductive agent and the negative electrode binder is (94-97): (0.5-1.5): (2.5-4.5);

[0019] and / or, the negative electrode active material comprises graphite;

[0020] And / or, the negative electrode binder comprises sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of (1.2-2.1):(1.3-2.4).

[0021] In some embodiments, the coating surface density of the negative electrode active slurry is 2-8 g / m 2 .

[0022] Among them, in the present application, increasing the pressure of the positive electrode can actually improve the energy density; at the same time, reducing the compaction of the negative electrode can improve the first efficiency, rate, and cycle; and then using the battery cell to first use a small current formation energy to form a dense SEI film to achieve an improvement in the comprehensive performance of the battery cell, thereby obtaining a gain effect in high-temperature storage, first efficiency, and cycle performance; at the same time, the method of the present application is simple and easy to implement, low cost, and has significant effects.

[0023] According to an embodiment of the second aspect of the present application, a battery cell is provided, which is prepared by the method described in any of the above embodiments.

[0024] In some embodiments, the battery cell includes a positive electrode sheet, a negative electrode sheet and a separator; wherein the compaction density of the positive electrode sheet is 2.4-2.8 g / cc; and the compaction density of the negative electrode sheet is 1.4-1.7 g / cc.

[0025] In some embodiments, the battery cell is first charged with a current of 0.1-0.5C for 3-30 minutes, and then charged with a current of 1.5-4C for 60-180 minutes to complete the charging.

[0026] The high-temperature storage performance of the battery cell in the present application is significantly improved, while overcoming the defects of the battery cell's first efficiency, energy density, and cycle performance deterioration, achieving the purpose of improving the first efficiency, high-temperature storage, and cycle performance.

[0027] According to an embodiment of the third aspect of the present application, a secondary battery is provided, which includes the battery cell in any of the above embodiments.

[0028] According to an embodiment of the fourth aspect of the present application, an electrical device is provided, which includes the secondary battery described in any of the above embodiments.

[0029] The present application applies battery cells with good comprehensive performance to secondary batteries, reduces the side reactions between the negative electrode and the electrolyte, is beneficial to improving the high-temperature storage of secondary batteries, and improves the defects of reduced first efficiency and poor rate performance.

[0030] The last aspect of the present application proposes an electrical device, in which a battery cell with good comprehensive performance is applied to a secondary battery, and the obtained secondary battery is assembled and applied to the electrical device to expand the temperature application range of the electrical device.

[0031] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0033] Figure 1 It is a flow chart of a method for preparing a battery cell provided in one embodiment of the present application. DETAILED DESCRIPTION

[0034] Embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be construed as limiting the present application. On the contrary, the present application includes all changes, modifications and equivalents that fall within the spirit and connotation of the appended claims.

[0035] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a 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 a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present 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 real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it 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.

[0036] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0037] To achieve the above-mentioned purpose, according to the embodiment of the first aspect of the present application, a method for preparing a battery cell is proposed. Figure 1 , including the following steps:

[0038] S1: providing a positive electrode slurry and applying it to prepare a positive electrode sheet; wherein the compaction density of the positive electrode sheet is 2.4-2.8 g / cc;

[0039] S2: providing negative electrode slurry and coating to prepare negative electrode sheet; wherein the compaction density of the negative electrode sheet is 1.4-1.7 g / cc;

[0040] S3: Prepare a battery cell by assembling the positive electrode sheet, the negative electrode sheet and the separator; firstly charge the battery cell with a current of 0.1-1C for 3-30 minutes; then charge the battery cell with a current of 1.5-4C for 60-180 minutes to complete the charge;

[0041] S4: The cells after formation are divided into different capacities and taken off the production line.

[0042] The positive electrode slurry provided in S1 includes a positive electrode active material, a positive electrode conductor and a positive electrode binder; wherein the mass ratio of the positive electrode active material, the positive electrode conductor and the positive electrode binder is (96-98): (0.5-1.5): (1.5-3.5). In some embodiments, the mass ratio of the positive electrode active material, the positive electrode conductor and the positive electrode binder is (96, 97, 98): (0.5, 0.6, 0.7, 0.8, 0.9, 0.1, 0.11, 0.12, 0.13, 0.14, 1.5): (1.5, 2, 2.5, 3, 3.5).

[0043] The positive electrode sheet in the present application includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material accounts for more than 95%. As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector. The double-sided coating surface density is 300-400g / m 2 To ensure that the coating surface density of the positive electrode slurry is 2-8g / m 2 .

[0044] For example, the coating surface density of the positive electrode slurry is 2 g / m 2 , 3g / m 2 , 4g / m 2 , 5g / m 2 , 6g / m 2 , 7g / m 2 , 8g / m 2 When the surface density of the positive electrode coating is too high, such as greater than 8g / m 2 When the actual N / P ratio is too low, the negative electrode sheets will be in excess, resulting in lithium plating during the cell rate and cycle; when the surface density of the positive electrode sheets is too small, the actual N / P ratio is too high, and the negative electrode sheets are in excess, resulting in reduced cell energy density and increased side reactions; the N / P ratio refers to the CB value, which refers to the molar ratio of the negative electrode active material to the positive electrode active material in a lithium-ion battery.

[0045] Among them, the positive current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0046] In some embodiments, the positive electrode active material in the positive electrode sheet of the present application can be a positive electrode active material for batteries well-known in the art. As an example, the positive electrode active material can include at least one of the following materials: As an example, the positive electrode active material can include, but is not limited to, lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), lithium iron pyrophosphate (Li2FeP2O7), lithium cobalt oxide (LiCoO2), spinel-type lithium manganese oxide (LiMn2O4), spinel-type lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4), layered lithium manganese oxide (LiMnO2), lithium nickel oxide (LiNiO2), lithium niobate (LiNbO2), lithium ferrite (LiFeO2), lithium manganate (LiMgO2), lithium calcium oxide (LiCaO2), lithium copper oxide (LiCuO2), lithium zinc oxide (LiZnO2), lithium molybdate (LiMoO2), lithium tantalate (LiTaO2), lithium tungstate (LiWO2), lithium nickel cobalt aluminum oxide (LiNi x Co y Al 1-x-y O2, 0 < x < 1, 0 < y < 1, 0 < x + y < 1, for example LiNi 0.8 Co 0.15 Al 0.05 O2), lithium nickel cobalt manganese oxide (LiNi x Co y Mn 1-x-y O2, 0 < x < 1, 0 < y < 1, 0 < x + y < 1, for example LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1O2, etc.), lithium-rich materials (such as lithium-rich nickel-cobalt-manganese oxide), manganese oxide (MnO2), vanadium oxide, sulfur oxide, silicate oxide, and at least one of their modified compounds. These materials can be used alone or in combination of two or more.

[0047] The modified compounds of the above-mentioned positive electrode active materials may be modified by doping, surface coating, or simultaneous doping and coating of the positive electrode active materials.

[0048] In some embodiments, the positive electrode film layer may also optionally include a positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0049] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0050] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, positive electrode conductor, positive electrode binder and any other components of the first aspect of the present application, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, a positive electrode sheet can be obtained, wherein the compaction density of the positive electrode sheet is 2.4-2.8g / cc.

[0051] In some embodiments, the compaction density of the positive electrode sheet is 2.4g / cc, 2.45g / cc, 2.5g / cc, 2.6g / cc, 2.7g / cc, 2.8g / cc, etc. The thickness of the positive electrode sheet is designed differently according to different compaction densities, such as a compaction density of 2.45g / cc, and a thickness of 0.165mm±0.002 corresponding to the thickness of the positive electrode sheet; for example, a compaction density of 2.55g / cc, and a thickness of 0.160mm±0.002 corresponding to the thickness of the positive electrode sheet; for example, a compaction density of 2.65g / cc, and a thickness of 0.155mm±0.002 corresponding to the thickness of the positive electrode sheet. Among them, the excessive thickness or thinness of the positive electrode plate affects its actual compaction density and thus affects the performance of the battery cell when it is used; for example, if the compaction density of the positive electrode plate is too large, such as greater than 2.8g / cc, it will cause the battery cell's first efficiency, gram capacity, rate performance, high-temperature storage, and cycle to deteriorate; if the compaction density of the positive electrode plate is too small, such as less than 2.4g / cc, it will cause the battery cell's energy density to be insufficient, the internal resistance of the positive electrode plate and the battery cell to be too large, and the discharge voltage platform to be low.

[0052] Wherein, the negative electrode active slurry provided in S2 includes a negative electrode active material, a negative electrode conductor and a negative electrode binder; wherein the mass ratio of the negative electrode active material, the negative electrode conductor and the negative electrode binder is (94-97): (0.5-1.5): (2.5-4.5); for example, the mass ratio of the negative electrode active material, the negative electrode conductor and the negative electrode binder is (94, 95, 96, 97): (0.5, 0.6, 0.7, 0.8, 0.9, 0.1, 0.11, 0.12, 0.13, 0.14, 1.5): (2.5, 3, 3.5, 4.5).

[0053] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material. As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector to ensure that the coating surface density of the positive electrode slurry is 2-8 g / m 2 .

[0054] For example, the coating surface density of the positive electrode slurry is 2 g / m 2 , 3g / m 2 , 4g / m 2 , 5g / m 2 , 6g / m 2 , 7g / m 2 , 8g / m 2 When the surface density of the positive electrode coating is too high, such as greater than 8g / m 2When the actual N / P ratio is too low, the positive electrode sheet will be excessive and insufficient, resulting in lithium deposition during the battery cell rate and cycle; when the surface density of the positive electrode sheet coating is too small, the actual N / P ratio is too high, and there are too many positive electrode sheets, resulting in reduced energy density of the battery cell and increased side reactions.

[0055] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0056] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: metallic lithium, artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0057] In some embodiments, the negative electrode film layer may also optionally include a negative electrode binder. The negative electrode 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). In some embodiments, the negative electrode binder includes sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in a mass ratio of (1.2-2.1): (1.3-2.4), for example, the mass ratio of sodium carboxymethyl cellulose and styrene-butadiene rubber is (1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1): (1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4).

[0058] In some embodiments, the negative electrode film layer may further include a negative electrode 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.

[0059] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0060] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the negative electrode conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing (rolling) and other processes, the negative electrode sheet can be obtained, wherein the compaction density of the negative electrode sheet is 1.4-1.7g / cc.

[0061] In some embodiments, the compaction density of the negative electrode sheet is 1.4g / cc, 1.45g / cc, 1.5g / cc, 1.6g / cc, 1.7g / cc, etc. For example, if the compaction density of the negative electrode sheet is too large, such as greater than 1.7g / cc, the first efficiency, rate performance, high temperature storage, electrode sheet wetting, and cycle of the battery cell will deteriorate; if the compaction density of the negative electrode sheet is too small, such as less than 1.4g / cc, the energy density of the battery cell, the negative electrode sheet, and the internal resistance of the battery cell will deteriorate.

[0062] In S3, a positive electrode sheet and a negative electrode sheet are assembled with a separator to prepare a battery cell, wherein the electrolyte plays a role of conducting ions between the positive electrode sheet and the negative electrode sheet. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0063] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0064] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0065] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0066] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0067] In some embodiments, the present application has no particular limitation on the type of the diaphragm, and any known porous structure diaphragm with good chemical stability and mechanical stability can be selected.

[0068] In some embodiments, the material of the diaphragm can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The diaphragm can be a single-layer film or a multi-layer composite film, without particular limitation. When the diaphragm is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0069] In some embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be made into a battery cell by a winding process or a lamination process, for example, the positive electrode sheet, the negative electrode sheet and the separator are cut into corresponding sizes, and then the bare battery cells are laminated, and then baked, injected, and left to stand to form the battery cell. Then, the battery cell is firstly charged with a current of 0.1-1C for 3-30 minutes, and then charged with a current of 1.5-4C for 60-180 minutes to complete the charge.

[0070] For example, the battery cell is first formed for 3-30 minutes using a constant current of 0.1C, 0.2C, 0.3C, 0.4C, 0.5C, 0.6C, 0.7C, 0.8C, 0.9C, 1C, etc.; the formation time can be 3min, 5min, 8min, 10min, 13min, 15min, 19min, 20min, 22min, 24min, 25min, 30min, etc. During the initial formation of the battery cell, if the current is too large, such as greater than 1C, the SEI film formed during the formation process is loose, the SEI structure is unstable, and the side reaction between the negative electrode and the electrolyte increases when the battery cell is used. If the current is too small, such as greater than 0.1C, on the one hand, the SEI film formed is too dense, reducing the initial efficiency, and on the other hand, the formation time is too long, affecting production efficiency. In addition, if the initial formation time of the battery cell is too long, such as greater than 30 minutes, the production efficiency will be reduced; on the contrary, if the initial formation time of the battery cell is less than 3 minutes, the time is too short and the film formation quality of the SEI film is poor.

[0071] For example, the battery cell is formed again with a current of 1.5-4C for 60-180 minutes; for example, the battery cell is formed again with a constant current of 1.5C, 1.6C, 1.7C, 1.8C, 1.9C, 2C, 2.3C, 2.4C, 3C, 3.3C, 4C, etc.; the forming time can be 60min, 80min, 100min, 130min, 150min, 160min, 170min, 180min, etc.

[0072] In S4, the cells will be divided into different capacities and taken off the production line after formation.

[0073] Among them, in the present application, increasing the pressure of the positive electrode can actually improve the energy density; at the same time, reducing the compaction of the negative electrode can improve the first efficiency, rate, and cycle; and then using the battery cell to first use a small current formation energy to form a dense SEI film to achieve an improvement in the comprehensive performance of the battery cell, thereby obtaining a gain effect in high-temperature storage, first efficiency, and cycle performance; at the same time, the method of the present application is simple and easy to implement, low cost, and has significant effects.

[0074] According to an embodiment of the second aspect of the present application, a battery cell is provided, which is prepared using the method in any of the above embodiments.

[0075] In some embodiments, the battery cell includes a positive electrode sheet, a negative electrode sheet and a separator; wherein the compaction density of the positive electrode sheet is 2.4-2.8 g / cc; and the compaction density of the negative electrode sheet is 1.4-1.7 g / cc. The battery cell is firstly charged with a current of 0.1-0.5C for 3-30 minutes; and then charged with a current of 1.5-4C for 60-180 minutes to complete the charge.

[0076] The high-temperature storage performance of the battery cell in the present application is significantly improved, while overcoming the defects of the battery cell's first efficiency, energy density, and cycle performance deterioration, achieving the purpose of improving the first efficiency, high-temperature storage, and cycle performance.

[0077] According to an embodiment of the third aspect of the present application, a secondary battery is provided, which includes the battery cell in any of the above embodiments. In some embodiments, the secondary battery may include an outer package. The outer package may be used to encapsulate the above electrode assembly and the electrolyte.

[0078] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0079] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape.

[0080] The present application applies battery cells with good comprehensive performance to secondary batteries, reduces the side reactions between the negative electrode and the electrolyte, is beneficial to improving the high-temperature storage of secondary batteries, and improves the defects of reduced first efficiency and poor rate performance.

[0081] According to an embodiment of the fourth aspect of the present application, an electrical device is provided, which includes the secondary battery in any of the above embodiments.

[0082] The last aspect of the present application proposes an electrical device, in which a battery cell with good comprehensive performance is applied to a secondary battery, and the obtained secondary battery is assembled and applied to the electrical device to expand the temperature application range of the electrical device.

[0083] To facilitate further understanding of the present application, the scheme of the present application is further described below in conjunction with the embodiments. Those skilled in the art will understand that the description in the present application is only part of the examples, and any other suitable specific examples are within the scope of the present application.

[0084] Example 1

[0085] This embodiment provides a battery cell, and its preparation method and specific operating parameters are as follows: lithium iron phosphate, a conductive agent and a binder are mixed in a mass ratio of 97:1:2 to prepare a positive electrode slurry with good fluidity, and the positive electrode slurry is heated to 380 g / m 2 Surface density coating, ensure that the coating surface density of the positive electrode slurry is 380±4g / m 2 According to the measured surface density and thickness of the positive electrode sheet after rolling, the compaction density of the positive electrode sheet is 2.55±0.02g / m 2 , the thickness of the positive electrode sheet is 0.160±0.002mm.

[0086] Graphite: conductive agent: CMC: SBR are mixed in a mass ratio of 96:1:1.4:1.6 to obtain a negative electrode slurry with good stability; the coating and rolling processes of the negative electrode slurry are based on the positive electrode sheet, and the compaction density of the negative electrode sheet is 1.6±0.02g / cc, and the thickness of the negative electrode sheet is 0.116±0.002mm.

[0087] The obtained positive and negative electrodes and separators are assembled into soft-pack cells and then subjected to baking, liquid injection, and static processes to obtain cells. The cell components are firstly formed by 0.25C current for 20 minutes, and then by 1.5C current for 130 minutes; and then the cells are separated by capacity and taken offline.

[0088] Example 2

[0089] This embodiment provides a battery cell, which is different from the embodiment 1 in the following aspects: the compaction density of the negative electrode plate is 1.5 g / cc.

[0090] Example 3

[0091] This embodiment provides a battery cell, which is different from the embodiment 1 in the following aspects: the compaction density of the positive electrode plate is 2.60 g / cc.

[0092] Example 4

[0093] This embodiment provides a battery cell, which is different from the embodiment 1 in the following aspects: the compaction density of the positive electrode plate is 2.65 g / cc.

[0094] Example 5

[0095] This embodiment provides a battery cell, which is different from Embodiment 1 in the following aspects: the compaction density of the positive electrode plate is 2.65g / cc, and the compaction density of the negative electrode plate is 1.5g / cc; the battery cell components are first formed using a 0.25C current for 10 minutes; then formed using a 1.5C current for 130 minutes; and then the battery cell is separated and taken offline.

[0096] Comparative Example 1

[0097] This comparative example provides a battery cell, whose preparation method and specific operating parameters are different from those of Example 1 as follows: graphite: conductive agent: CMC: SBR are mixed in a mass ratio of 96:1:1.4:1.6 to obtain a negative electrode slurry with good stability; wherein the coating and rolling process of the negative electrode slurry refers to the positive electrode sheet, and the compaction density of the negative electrode sheet is 1.3±0.02g / cc, and the thickness of the negative electrode sheet is 0.142±0.002mm.

[0098] The prepared positive and negative electrodes and separators are assembled into soft-pack cells and then subjected to baking, liquid injection, and static processes to obtain cells. The cell components are firstly formed using a 0.5C current for 10 minutes, and then formed using a 1.5C current for 130 minutes; and then the cells are separated and taken offline.

[0099] Comparative Example 2

[0100] This comparative example provides a battery cell, whose preparation method and specific operating parameters are different from those of Example 1 as follows: the battery cell components are first formed using a 2C current for 10 minutes; then formed using a 4.5C current for 130 minutes; and then the battery cell is separated and taken offline.

[0101] Comparative Example 3

[0102] This comparative example provides a battery cell, and its preparation method and specific operating parameters are different from those of Example 1 as follows: lithium iron phosphate, a conductive agent and a binder are mixed in a mass ratio of 97:1:2 to prepare a positive electrode slurry with good fluidity, and the positive electrode slurry is heated to 380 g / m2 Surface density coating, ensure that the coating surface density of the positive electrode slurry is 380±4g / m 2 According to the measured surface density and thickness of the positive electrode sheet after rolling, the compaction density of the positive electrode sheet is 2.3±0.02g / m 2 The thickness of the positive electrode sheet is 0.178±0.002mm.

[0103] The prepared positive and negative electrodes and separators are assembled into soft-pack cells and then subjected to baking, liquid injection, and static processes to obtain cells. The cell components are firstly formed using a 0.5C current for 10 minutes, and then formed using a 1.5C current for 130 minutes; and then the cells are separated and taken offline.

[0104] Test Case

[0105] The battery cells prepared in the above embodiments and comparative examples were subjected to cycle performance testing. The cycle test was conducted under a constant pressure of 100KG, a charge and discharge rate of 1C, a voltage of 2.5-3.65V, a charging mode of constant current and constant voltage, a cut-off current of 0.05C, and the cycle was performed until the capacity was attenuated to 80% of the initial capacity. All tests were conducted at room temperature, and the results are shown in Table 1.

[0106] Table 1 Test results of battery cells made from battery cells in various embodiments and comparative examples.

[0107]

[0108] It can be seen from Table 1 that Comparative Examples 1-3 exceed the conventional parameter values ​​in terms of negative electrode compaction, low current formation, and positive electrode compaction, respectively, and the performance is poor in energy density, high temperature storage, and comprehensive aspects; Example 1 is compared with Comparative Example 1, and the energy density, 3C charging capacity retention rate, and 55℃7D storage capacity retention and recovery rate values ​​of Example 1 are all increased, but the first effect and cycle capacity retention rates are all reduced; Example 5 is the optimal embodiment, and its energy density, first effect, 3C charging capacity retention rate, 55℃7D storage capacity retention and recovery rate values, and cycle capacity retention rate are all increased, and the performance is the best. Therefore, this application achieves the effect of improving various performance indicators through comprehensive measures of small current formation, positive electrode compaction, and negative electrode pressure reduction.

[0109] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0110] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for preparing a battery cell, characterized in that: The following steps are included Providing a positive electrode slurry and applying it to prepare a positive electrode sheet; wherein the compaction density of the positive electrode sheet is 2.4-2.8 g / cc; Providing a negative electrode slurry and applying it to prepare a negative electrode sheet; wherein the compaction density of the negative electrode sheet is 1.4-1.7 g / cc; The positive electrode sheet and the negative electrode sheet are assembled with a separator to prepare a battery cell; the battery cell is firstly charged with a current of 0.1-1C for 3-30 minutes; and then charged with a current of 1.5-4C for 60-180 minutes to complete the charging; The cells after formation are divided into different capacities and taken off the production line.

2. The preparation method according to claim 1, characterized in that: The positive electrode slurry comprises a positive electrode active material, a positive electrode conductor and a positive electrode binder; And / or, the mass ratio of the positive electrode active material, the positive electrode conductive agent and the positive electrode binder is (96-98): (0.5-1.5): (1.5-3.5); And / or, the positive electrode active material includes lithium iron phosphate.

3. The preparation method according to claim 1 or 2, characterized in that: The coating surface density of the positive electrode slurry is 2-8 g / m 2 .

4. The preparation method according to claim 1, characterized in that: The negative electrode active slurry comprises a negative electrode active material, a negative electrode conductive agent and a negative electrode binder; And / or, the mass ratio of the negative electrode active material, the negative electrode conductive agent and the negative electrode binder is (94-97): (0.5-1.5): (2.5-4.5); and / or, the negative electrode active material comprises graphite; And / or, the negative electrode binder comprises sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of (1.2-2.1):(1.3-2.4).

5. The preparation method according to claim 1 or 4, characterized in that: The coating surface density of the negative electrode active slurry is 2-8 g / m 2 .

6. A battery cell, characterized in that: The method is prepared by any one of claims 1 to 5.

7. The battery cell according to claim 6, characterized in that: It comprises a positive electrode sheet, a negative electrode sheet and a separator; wherein the compaction density of the positive electrode sheet is 2.4-2.8 g / cc; and the compaction density of the negative electrode sheet is 1.4-1.7 g / cc.

8. The battery cell according to claim 7, characterized in that: The battery cell is firstly charged with a current of 0.1-0.5C for 3-30 minutes, and then charged with a current of 1.5-4C for 60-180 minutes to complete the charging.

9. A secondary battery, characterized in that: The secondary battery comprises the battery cell according to any one of claims 6 or 7.

10. An electrical device, characterized in that: The secondary battery according to claim 9 is included.

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