Negative pole piece and preparation method thereof, battery monomer, battery module and electric equipment

Abstract

The invention discloses a negative pole piece and a preparation method thereof, a battery monomer, a battery module and electric equipment, and belongs to the technical field of batteries, and the preparation method comprises the following steps: determining expandable space parameters of the battery monomer; according to the expandable space parameters and a preset negative electrode expansion relational expression, the binder proportion of the negative electrode piece in the battery monomer is determined, and the binder proportion in the preset negative electrode expansion relational expression and the expansion amount of the electrode piece are in an inverse relation; dissolving the binder, the silicon-carbon negative electrode material and the conductive agent in a solvent according to the proportion of the binder, and preparing negative electrode slurry; and coating at least one surface of a negative electrode current collector with the negative electrode slurry to obtain the negative electrode plate. The embodiment of the invention can prolong the cycle life of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a negative electrode sheet, a preparation method thereof, a battery monomer, a battery module and a power consumption device. BACKGROUND

[0002] With the increasing demand for energy density and long life of lithium ion batteries, silicon negative electrode materials have attracted much attention due to their high specific capacity characteristics. Compared with graphite negative electrodes, silicon materials have a high theoretical specific capacity (4200 mAh / g) and have certain application prospects. However, silicon will undergo a huge volume expansion during charging and discharging, which will easily cause the pulverization and breakage of silicon particles, and even the detachment of silicon particles from the current collector, resulting in rapid capacity decay and a significant reduction in cycle life.

[0003] Although the use of silicon-carbon composite negative electrodes prepared by mixing silicon and graphite in a certain proportion can alleviate the problem of volume expansion of silicon to some extent, the long-term volume expansion and contraction of silicon will still cause the disconnection of the internal conductive network of the electrode, thereby reducing the cycle life of the battery. SUMMARY

[0004] The main purpose of the present application is to provide a negative electrode sheet, a preparation method thereof, a battery monomer, a battery module and a power consumption device, which aims to solve the technical problem that the volume expansion and contraction of silicon materials during battery cycling is too large, resulting in a reduction in the cycle life of the battery.

[0005] To achieve the above-mentioned purpose, the present application provides a preparation method of a negative electrode sheet, comprising:

[0006] determining an expandable space parameter of a battery monomer;

[0007] determining a binder proportion of a negative electrode sheet in the battery monomer according to the expandable space parameter and a preset negative electrode expansion relationship, wherein the binder proportion and the sheet expansion amount in the preset negative electrode expansion relationship are inversely proportional;

[0008] taking a binder according to the binder proportion, and dissolving a silicon-carbon negative electrode material and a conductive agent in a solvent to prepare a negative electrode slurry;

[0009] coating the negative electrode slurry to at least one surface of a negative electrode current collector to obtain a negative electrode sheet.

[0010] In some embodiments of the present application, the preset negative electrode expansion relationship satisfies: S EOL =((-2.7797X+0.2102+0.12+1)*0.1012*64+7.28) / 14.98), wherein S EOL is the expansion amount of the negative electrode sheet in the battery monomer at the end of the battery life cycle, and x is the binder proportion.

[0011] In some embodiments of the present application, the step of determining the expandable space parameter of the battery monomer comprises:

[0012] obtaining the assembly size of the battery module to which the battery monomer belongs, and determining the reserved space of the battery monomer according to the assembly size;

[0013] obtaining the expandable space parameter according to the reserved space and the tab thickness of the battery monomer.

[0014] In some embodiments of the present application, the binder comprises at least one of styrene butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan.

[0015] In some embodiments of the present application, the negative electrode tab comprises the negative electrode current collector and the negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer comprises 0.5-3% of the binder, 0.5-1.5% of the conductive agent, and the rest is the silicon-carbon negative electrode material, in terms of mass percentage.

[0016] In some embodiments of the present application, the silicon material accounts for 3-10% of the silicon-carbon negative electrode material, and the rest is the carbon material, in terms of mass percentage.

[0017] In some embodiments of the present application, the silicon material comprises at least one of elemental silicon, silicon oxide compound, silicon-nitrogen compound and silicon alloy.

[0018] The present application also provides a negative electrode tab prepared by the preparation method of the negative electrode tab as described above, which comprises the negative electrode current collector and the negative electrode film layer arranged on at least one surface of the negative electrode current collector.

[0019] The present application also provides a battery monomer comprising the positive electrode tab, the negative electrode tab, the electrolyte and the separator film, wherein the negative electrode tab is the negative electrode tab as described above, and the positive electrode tab comprises the positive electrode current collector and the positive electrode film layer arranged on at least one surface of the positive electrode current collector.

[0020] The positive electrode film layer comprises the positive electrode active material, and the positive electrode active material comprises at least one of lithium-containing phosphate, modified lithium-containing phosphate, lithium transition metal oxide and modified lithium transition metal oxide.

[0021] The present application also provides a battery module comprising the shell and a plurality of battery monomers as described above packaged in the shell, wherein the battery monomers are stacked in the thickness direction.

[0022] This application also provides an electrical device, including the battery module as described above.

[0023] The method for preparing the negative electrode sheet provided in this application embodiment determines the expandable space parameter of the battery cell, which can represent the allowable expansion space of the battery cell; according to the expandable space parameter and the preset negative electrode expansion relationship, the proportion of binder in the negative electrode sheet of the battery cell is determined. Silicon in silicon-carbon negative electrode material will produce a large volume expansion, while binder can generate a certain mechanical binding force on silicon-carbon negative electrode material to prevent silicon-carbon negative electrode material from falling off. Therefore, under the guidance of the preset negative electrode expansion relationship, the expansion amount of the battery cycle in different life cycles can be adjusted by adding the amount of binder; binder is taken according to the binder proportion, and silicon-carbon negative electrode material and conductive agent are dissolved in solvent to prepare negative electrode slurry; the negative electrode slurry is coated onto at least one surface of the negative electrode current collector to obtain the negative electrode sheet. Based on the allowable expansion space of the battery cell, this application starts from the composition regulation of the negative electrode sheet to control the expansion of the negative electrode sheet. This allows the expansion amount of the battery cell to be adjusted within the allowable expansion space throughout its entire life cycle, alleviating the long-term volume expansion and contraction problem of silicon-containing negative electrode materials, reducing the probability of the conductive network inside the electrode being disconnected, and improving the cycle life of the battery cell. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments or related technologies of this drawing, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this drawing. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0025] Figure 1 This is a schematic flowchart of the method for preparing the negative electrode sheet according to an embodiment of this application;

[0026] Figure 2 The graph shows the cycle performance test results of the batteries prepared in Examples 1-2 and Comparative Examples 1-2 of this application.

[0027] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0028] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode sheet and its preparation method, battery cell, battery module, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0029] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0030] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0031] Compared to graphite anodes, silicon has a higher theoretical specific capacity, making it a very promising new anode material. However, silicon undergoes significant volume expansion during charging and discharging, which easily leads to the pulverization and breakage of silicon particles, and even their detachment from the current collector, resulting in rapid capacity decay and a significantly shortened cycle life.

[0032] While mixing silicon and graphite in a certain proportion can alleviate the volume expansion problem of silicon to some extent, the long-term expansion and contraction of silicon-based materials can still lead to the breakage of the conductive network inside the electrode, thereby reducing the cycle life of the battery. Furthermore, although fabricating porous silicon or nano-silicon can better mitigate the volume expansion of silicon, this method is often complex and costly, making it unsuitable for large-scale production.

[0033] Based on this, this application proposes a method for preparing a negative electrode sheet. By determining the expandable space parameters of a battery cell, the expansion space data reserved at the battery cell level is obtained. According to the expandable space parameters and a preset negative electrode expansion formula, the binder ratio of the negative electrode sheet in the battery cell is determined. The preset negative electrode expansion formula can be obtained through prior testing; therefore, under the guidance of the preset negative electrode expansion formula, the binder ratio corresponding to the expandable space parameters can be obtained. The binder is then taken according to this binder ratio, and silicon-carbon negative electrode material and conductive agent are dissolved in… In a solvent, a negative electrode slurry is prepared, containing a suitable mass fraction of binder. The negative electrode slurry is then coated onto at least one surface of the negative electrode current collector to obtain a negative electrode sheet. This achieves the purpose of controlling the expansion amount of the electrode layer by adjusting the material layer composition ratio. The negative electrode sheet is further prepared into a battery cell, and then the battery cell is assembled into a battery module. This allows for the control of both the battery layer and the module layer, adapting to the allowable expansion space of the battery cell, reducing the probability of silicon material in the negative electrode sheet falling off due to volume expansion and contraction, and improving the cycle life of the battery.

[0034] This application provides a method for preparing a negative electrode sheet, referring to... Figure 1 , Figure 1 This is a schematic flowchart illustrating a method for preparing a negative electrode sheet according to an embodiment of this application.

[0035] In this embodiment, the method for preparing the negative electrode sheet includes the following steps S10 to S40:

[0036] Step S10: Determine the expandable space parameters of the battery cell;

[0037] The expandable space parameter refers to a parameter characterizing the allowable expansion space of a single battery cell. Understandably, in scenarios requiring high power and high energy density, a single battery cell cannot provide sufficient power, necessitating the assembly of multiple cells into a battery module. A certain gap can be reserved between the individual battery cells within the battery module, and a gap can also be reserved between the battery module casing and the battery cells. These gaps, accommodating the volume expansion of the battery, can all be included within the expandable space range, thus determining the expandable space parameter. Different types of battery cells, with varying specifications and assembly methods, will have different reserved expandable spaces. The expandable space parameter can be expressed in various ways; for example, the gap size between battery cells can be used as the expandable space parameter, or the reserved gap can be converted into a percentage of the dimension of the battery cell in the direction of expansion.

[0038] In some embodiments of this application, step S10 includes the following steps S11 to S12:

[0039] Step S11: Obtain the assembly dimensions of the battery module to which the battery cell belongs, and determine the reserved space of the battery cell based on the assembly dimensions.

[0040] Assembly dimensions refer to the dimensional parameters for assembling individual battery cells into a battery module. Reserved space refers to the clearance space reserved for individual battery cells within the battery module. It is understood that individual battery cells can have various shapes, such as cylindrical or square. Square batteries are easier to assemble; this embodiment uses a square battery cell as an example. A square battery cell has dimensions in three directions: height, width, and thickness. During assembly, the battery cells can be stacked along the thickness direction and encapsulated to form a battery module. A certain gap can be set between every two adjacent battery cells, and between the battery cell and the inner surface of the battery module's outer casing. This gap serves as reserved space. Therefore, the reserved space for the battery cells can be obtained by setting relevant parameters in the assembly dimensions. The gaps between battery cells can be set in various ways. For example, positioning elements can be set on the outer surface of the bottom of the battery cell. During assembly, the positioning elements of two adjacent battery cells are brought into contact, thus forming a gap between the outer surfaces of the battery cells and also between the battery cell and the inner surface of the battery module's outer casing. A positioning structure can also be set on the inner surface of the battery module's casing. The positioning structure is used to define the assembly position of the battery cells, and the positioning structure makes gaps form between adjacent battery cells.

[0041] Step S12: Obtain the expandable space parameters based on the reserved space and the electrode thickness of the battery cell.

[0042] Understandably, in the process of manufacturing battery cells, positive electrode sheets, separators, and negative electrode sheets are wound or stacked to form a cell, which is then immersed in electrolyte. For each battery cell, the reserved space allocation at the battery module level can be the same, and the battery cells assembled in the battery module are of the same specification, with similar expansion amounts. Therefore, the expandable space parameter can be obtained based on the reserved space and electrode thickness. During battery cycling, the insertion and extraction of lithium ions at the negative electrode directly leads to the volume expansion of the negative electrode material. This volume expansion causes an increase in the thickness of the negative electrode sheet, which in turn leads to the volume expansion of the battery. The volume expansion at the negative electrode material level is difficult to measure directly, so the change in electrode layer thickness can be used to characterize the magnitude of the expansion at the negative electrode material level. For example, dividing the reserved space by the electrode thickness of the battery cell yields the electrode expandable percentage data, which can be used as the expandable space parameter.

[0043] Step S20: Based on the expandable space parameters and the preset negative electrode expansion formula, determine the binder ratio of the negative electrode sheet in the battery cell. In the preset negative electrode expansion formula, the binder ratio and the electrode sheet expansion amount are inversely proportional.

[0044] The preset negative electrode expansion formula is an expression representing the relationship between the expansion amount of the negative electrode sheet and the amount of binder added. It can be understood that the binder is an additive used in the negative electrode sheet preparation process, enhancing the adhesion of the film layer on the surface of the negative electrode current collector. When silicon undergoes volume expansion, the binder can exert a certain mechanical binding force, slowing down the detachment of silicon caused by volume expansion. The amount of binder added to the negative electrode sheet has a certain impact on the expansion amount of the battery cell. The preset negative electrode expansion formula shows that the higher the binder ratio, the smaller the electrode sheet expansion. Substituting the expandable space parameter into the preset negative electrode expansion formula yields the binder ratio of the negative electrode sheet.

[0045] In some embodiments of this application, the binder includes at least one selected from styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan. It is understood that the above-mentioned binders all possess strong adhesive properties and can restrain the volume expansion of silicon during battery charging and discharging. Different types of binders can be selected based on requirements such as the strength of the adhesive force and cost.

[0046] In some embodiments of this application, the preset negative electrode expansion relationship is expressed as follows: S EOL = ((-2.7797X+0.2102+0.12+1)*0.1012*64+7.28) / 14.98), where EOL (End of Life) represents the end of the life cycle, and S EOL This represents the expansion of the negative electrode sheet during cycling to the end of the battery's life cycle, where x represents the proportion of binder.

[0047] Correspondingly, S BOL = ((-2.7797X+0.2102)*0.1012*64+7.28) / 14.98, where BOL (Beginning of Life) represents the early stage of the life cycle, and S BOL This represents the expansion amount of the negative electrode sheet in the early stage of the battery's life cycle, where x represents the proportion of binder. Compared to the early stage of the battery's life cycle, the final stage requires an additional 12% fixed expansion on top of the initial expansion.

[0048] Understandably, this application systematically studied the expansion behavior of negative electrode materials during battery cycling through experiments. It combined this with cycling tests of negative electrode sheets with different binder contents in pouch cells throughout their entire lifecycle (from BOL to EOL), collecting data on their volume expansion rate at the EOL stage. Based on multiple sets of experimental results, a pre-defined negative electrode expansion relationship was established through data fitting, regression analysis, and other processing methods. This relationship can be used to optimize negative electrode formulation design and improve battery cycle life and safety.

[0049] Step S30: Take the binder according to the binder ratio, and dissolve the silicon-carbon anode material and conductive agent in the solvent to prepare the anode slurry;

[0050] Silicon-carbon anode materials can facilitate the insertion and extraction of lithium ions during cycling. Conductive agents primarily enhance conductivity. In addition to binders and conductive agents, the anode slurry can also include other types of additives, such as the thickener sodium carboxymethyl cellulose. The type of additive can be selected based on the requirements for the preparation of the anode sheet.

[0051] In some embodiments of this application, the negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer comprises, by mass percentage, 0.5-3% binder, 0.5-1.5% conductive agent, and the remainder being silicon-carbon negative electrode material. For example, the proportion of binder in the negative electrode film layer can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any range thereof. The proportion of conductive agent can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, or any range thereof. If the proportion of binder in the negative electrode film layer is too low, the adhesion between the negative electrode film layer and the negative current collector is reduced, easily leading to the problem of negative electrode material detachment. Conversely, if the proportion of binder is too high, it will reduce the amount of silicon-carbon negative electrode material added, affecting the lithium-ion insertion and extraction performance of the negative electrode. If the proportion of conductive agent is too low, it will affect the conductivity of the negative electrode film; if the proportion of conductive agent is too high, it will reduce the amount of silicon-carbon negative electrode material to be added, thus affecting the performance of the negative electrode. Controlling the proportions of binder and conductive agent within a suitable range ensures that the binder can alleviate the volume expansion problem of the silicon-carbon negative electrode material without significantly impacting the performance of the negative electrode.

[0052] In some embodiments of this application, the silicon content in the silicon-carbon anode material is 3-10% by mass, with the remainder being carbon material. For example, the silicon content in the silicon-carbon anode material can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any range thereof. If the silicon content in the silicon-carbon anode material is too low, the overall specific capacity improvement is minimal; conversely, if the silicon content is too high, conductivity decreases, rate performance declines, and volume expansion becomes more severe. An appropriate silicon content can improve the specific capacity of the anode material while avoiding excessive volume expansion and providing sufficient conductivity.

[0053] In some embodiments of this application, the silicon material includes at least one of elemental silicon, silicon oxide compounds, silicon-nitrogen composites, and silicon alloys. It is understood that the silicon-carbon anode material can be a composite of silicon and carbon materials, and the silicon material can be one or more of the types listed above.

[0054] In some embodiments of this application, 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.

[0055] Step S40: The negative electrode slurry is coated onto at least one surface of the negative electrode current collector to obtain a negative electrode sheet.

[0056] The negative electrode current collector can be made of metal foil, such as copper foil. The negative electrode slurry is uniformly coated on the surface of the negative electrode current collector, and can also be dried and cold-pressed to finally obtain the negative electrode sheet.

[0057] In this embodiment, the expandable space parameter of the battery cell is determined, which represents the allowable expansion space of the battery cell. Based on the expandable space parameter and a preset negative electrode expansion formula, the binder ratio of the negative electrode sheet in the battery cell is determined. In the preset negative electrode expansion formula, the binder ratio and the electrode sheet expansion amount are inversely proportional. Silicon in the silicon-carbon negative electrode material will experience significant volume expansion, while the binder can exert a certain mechanical binding force on the silicon-carbon negative electrode material, preventing it from detaching. Therefore, under the guidance of the preset negative electrode expansion formula, the expansion amount of the battery cycle in different life cycles can be adjusted by adding the amount of binder. The binder is taken according to the specified binder ratio, and the silicon-carbon negative electrode material and conductive agent are dissolved in a solvent to prepare a negative electrode slurry. The negative electrode slurry is coated onto at least one surface of the negative electrode current collector to obtain a negative electrode sheet. Based on the allowable expansion space of the battery cell, this application starts from the composition regulation of the negative electrode sheet to control the expansion of the negative electrode sheet. This allows the expansion amount of the battery cell to be adjusted within the allowable expansion space throughout its entire life cycle, alleviating the long-term volume expansion and contraction problem of silicon-containing negative electrode materials, reducing the probability of the conductive network inside the electrode being disconnected, and improving the cycle life of the battery cell.

[0058] This application also provides a negative electrode sheet, prepared using the method described above. The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. In this application embodiment, the binder ratio in the negative electrode film layer is determined based on the expandable space parameters of the battery cell, allowing adjustment of the battery's expansion amount during different life cycles. The beneficial effects achieved are similar to those described in the above embodiments and will not be repeated here.

[0059] This application also provides a battery cell, including a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode is as described above. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes at least one of lithium phosphate, modified lithium phosphate, lithium transition metal oxide, and modified lithium transition metal oxide.

[0060] In some embodiments of this application, examples of lithium phosphates may include at least one of lithium iron phosphate (e.g., LiFePO4), lithium iron phosphate and carbon composites, lithium manganese phosphate (e.g., LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium transition metal oxides may include lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.1 Al 0.05 At least one of O2 and its modified compounds.

[0061] In some embodiments of this application, the electrolyte comprises an electrolyte salt and a solvent. The electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate. The solvent may include at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0062] In some embodiments of this application, the material of the separator may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0063] A single battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through. The positive electrode active material in this embodiment can be selected from a wide range of options. The beneficial effects achievable by the battery cell in this embodiment are the same as those described in the previous embodiments and will not be repeated here.

[0064] This application also provides a battery module, including a housing and a plurality of battery cells as described above, encapsulated within the housing, wherein the battery cells are stacked along the thickness direction. It is understood that during the encapsulation process of the battery module, expansion gaps can be provided between adjacent battery cells and between the battery cells and the inner surface of the module housing, allowing the battery cells to expand within a certain spatial range. The beneficial effects achievable by the battery module of this application are the same as those described in the above embodiments, and will not be repeated here.

[0065] This application also provides an electrical device, including the battery module described above. The electrical device can include various types of 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., but is not limited thereto. The beneficial effects achievable by the electrical device in this application are the same as those described in the above embodiments, and will not be repeated here.

[0066] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0067] Example 1

[0068] (1) The space reserved for the battery at the module level is determined to be 0.643 mm. Based on the reserved space, the expandable space of the battery from cycle to EOL is calculated to be 104.3%. Therefore, the maximum value of the expandable space reserved for the battery from EOL (i.e., S) is... EOL The value is 104.3%, according to the preset negative electrode expansion relationship:

[0069] S EOL =((-2.7797X+0.2102+0.12+1)*0.1012*64+7.28) / 14.98, the calculated adhesive content is 1.5%;

[0070] (2) The above raw materials are dissolved in a solvent and mixed to prepare a negative electrode sheet according to the following proportions: silicon-carbon negative electrode material 97.25% (of which graphite accounts for 97% and silicon material accounts for 3%), binder PAA 1.5%, conductive agent SP 1%, and conductive agent single-wall carbon nanotube 0.25%.

[0071] (3) Cut, punch and dry the positive electrode and negative electrode in sequence, and assemble them into soft pack batteries. The positive electrode uses NCM622 positive electrode and the negative electrode is the negative electrode prepared in the above steps. Electrolyte is injected.

[0072] (4) After the liquid injection is completed, place it in a 45℃ oven for 48 hours.

[0073] Example 2

[0074] (1) The space reserved for the battery at the module level is determined to be 0.4 mm. Based on the reserved space, the expandable space of the battery from cycle to EOL is calculated to be 102.7%. Therefore, the maximum value of the expandable space reserved for the battery from EOL (i.e., S) is... EOL The value is 102.6%, according to the preset negative electrode expansion relationship:

[0075] S EOL =((-2.7797X+0.2102+0.12+1)*0.1012*64+7.28) / 14.98, the calculated adhesive content is 2.9%;

[0076] (2) The above raw materials are dissolved in a solvent and mixed to prepare a negative electrode sheet according to the following proportions: silicon-carbon negative electrode material 95.75% (of which graphite accounts for 97% and silicon material accounts for 3%), binder PAA accounts for 3%, conductive agent SP accounts for 1%, and conductive agent single-wall carbon nanotubes accounts for 0.25%.

[0077] (3) Cut, punch and dry the positive electrode and negative electrode in sequence, and assemble them into soft pack batteries. The positive electrode uses NCM622 positive electrode and the negative electrode is the negative electrode prepared in the above steps. Electrolyte is injected.

[0078] (4) After the liquid injection is completed, place it in a 45℃ oven for 48 hours.

[0079] Comparative Example 1

[0080] (1) The space reserved for the battery at the module level is determined to be 0.643 mm. Based on the reserved space, the expandable space of the battery from cycle to EOL is calculated to be 104.3%. Therefore, the maximum value of the expandable space reserved for the battery from EOL (i.e., S) is... EOL The value is 104.3%, according to the preset negative electrode expansion relationship:

[0081] S EOL =((-2.7797X+0.2102+0.12+1)*0.1012*64+7.28) / 14.98), the theoretical proportion of adhesive is calculated to be 1.5%;

[0082] (2) The raw materials are dissolved in a solvent and mixed to prepare a negative electrode sheet according to the following proportions: silicon-carbon negative electrode material 97.25% (of which graphite accounts for 97% and silicon material accounts for 3%), binder PAA accounts for 1% (that is, lower than the theoretical proportion of binder 1.5% calculated by step (1) above), conductive agent SP accounts for 1.5% and conductive agent single-wall carbon nanotubes accounts for 0.25%.

[0083] (3) Cut, punch and dry the positive electrode and negative electrode in sequence, and assemble them into soft pack batteries. The positive electrode uses NCM622 positive electrode and the negative electrode is the negative electrode prepared in the above steps. Electrolyte is injected.

[0084] (4) After the liquid injection is completed, place it in a 45℃ oven for 48 hours.

[0085] Comparative Example 2

[0086] (1) The space reserved for the battery at the module level is determined to be 0.643 mm. Based on the reserved space, the expandable space of the battery from cycle to EOL is calculated to be 104.3%. Therefore, the maximum value of the expandable space reserved for the battery from EOL (i.e., S) is... EOL The value is 104.3%, according to the preset negative electrode expansion relationship:

[0087] S EOL =((-2.7797X+0.2102+0.12+1)*0.1012*64+7.28) / 14.98, the theoretical proportion of adhesive is calculated to be 1.5%;

[0088] (2) The raw materials are dissolved in a solvent and mixed to prepare a negative electrode sheet according to the following proportions: silicon-carbon negative electrode material 97.25% (of which graphite accounts for 97% and silicon material accounts for 3%), binder PAA accounts for 2% (that is, higher than the theoretical proportion of binder calculated by step (1) above by 1.5%), conductive agent SP accounts for 0.5% and conductive agent single-wall carbon nanotubes accounts for 0.25%.

[0089] (3) Cut, punch and dry the positive electrode and negative electrode in sequence, and assemble them into soft pack batteries. The positive electrode uses NCM622 positive electrode and the negative electrode is the negative electrode prepared in the above steps. Electrolyte is injected.

[0090] (4) After the liquid injection is completed, place it in a 45℃ oven for 48 hours.

[0091] Battery performance testing: Batteries prepared in Examples 1-2 and Comparative Examples 1-2 were subjected to 1C / 1C cycle testing at 45°C, and the results are shown in Table 1 below. Figure 2 The test results are shown.

[0092] Table 1

[0093] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Cycling data 360 cls @ 94.89% 360 cls @ 93.41% 360 cls @ 89.5% 360 cls @ 90.78%

[0094] Where cls stands for cycles, and @ represents "under certain conditions", therefore, according to Table 1, the battery capacity retention rate of Example 1 after 360 cycles is 94.89%; the battery capacity retention rate of Example 2 after 360 cycles is 93.41%; the battery capacity retention rate of Comparative Example 1 after 360 cycles is 89.5%; and the battery capacity retention rate of Comparative Example 2 after 360 cycles is 90.78%. Figure 2 The graph shows the cycle performance test results of Examples 1-2 and Comparative Examples 1-2. Figure 2 The horizontal axis represents the number of cycles, and the vertical axis represents the capacity retention rate.

[0095] Combining Table 1 and Figure 2 The test results show that the batteries of Examples 1-2 can maintain a higher capacity than the batteries of Comparative Examples 1-2 at the same number of cycles, with a slower capacity decay rate and a longer cycle life than the batteries of Comparative Examples 1-2.

[0096] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a negative electrode sheet, characterized in that, The method for preparing the negative electrode sheet includes: Determine the expandable space parameters of individual battery cells; The proportion of binder in the negative electrode sheet of the battery cell is determined based on the expandable space parameters and the preset negative electrode expansion formula. Take the binder according to the specified binder ratio, and dissolve the silicon-carbon anode material and conductive agent in a solvent to prepare the anode slurry; The negative electrode slurry is coated onto at least one surface of the negative electrode current collector to obtain a negative electrode sheet.

2. The method for preparing the negative electrode sheet as described in claim 1, characterized in that, The preset negative electrode expansion formula satisfies: S EOL =((-2.7797X+0.2102+0.12+1)*0.1012*64+7.28) / 14.98), where S EOL x represents the expansion amount of the negative electrode sheet in the battery cell during cycling to the end of the battery's life cycle, and x represents the proportion of the binder.

3. The method for preparing the negative electrode sheet as described in claim 1, characterized in that, The steps for determining the expandable space parameters of a single battery cell include: Obtain the assembly dimensions of the battery module to which the battery cell belongs, and determine the reserved space for the battery cell based on the assembly dimensions; The expandable space parameters are obtained based on the reserved space and the electrode thickness of the battery cell.

4. The method for preparing the negative electrode sheet as described in claim 1, characterized in that, The adhesive includes at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

5. The method for preparing the negative electrode sheet as described in claim 1, characterized in that, The negative electrode sheet includes the negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. By mass percentage, the negative electrode film layer includes 0.5-3% binder, 0.5-1.5% conductive agent, and the remainder is silicon-carbon negative electrode material.

6. The method for preparing the negative electrode sheet as described in claim 1, characterized in that, By mass percentage, the silicon material in the silicon-carbon anode material accounts for 3-10%, and the remainder is carbon material.

7. The method for preparing the negative electrode sheet as described in claim 6, characterized in that, The silicon material includes at least one of elemental silicon, silicon oxide, silicon-nitrogen composite, and silicon alloy.

8. A negative electrode sheet, characterized in that, The negative electrode sheet is prepared by the method described in any one of claims 1 to 7, wherein the negative electrode sheet comprises a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

9. A single battery cell, characterized in that, It includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode is the negative electrode as described in claim 8, and the positive electrode includes a positive current collector and a positive film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes at least one of lithium phosphate, modified lithium phosphate, lithium transition metal oxide, and modified lithium transition metal oxide.

10. A battery module, characterized in that, It includes a housing and a plurality of battery cells as described in claim 9 encapsulated within the housing, the battery cells being stacked along the thickness direction.

11. An electrical appliance, characterized in that, Includes the battery module as described in claim 10.

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