Battery

Abstract

The invention discloses a battery, and relates to the field of batteries. The battery comprises a naked battery cell, a bonding piece and a shell, the naked battery cell comprises an electrolyte, the electrolyte comprises a lithium salt and a mixed solvent, and the mixed solvent comprises a carboxylic ester solvent with the mass fraction of A, an additive with the mass fraction of A1 and the balance of a carbonic ester solvent; 1.7 < = (A + A1) / B < = 4.7, C-B > = 0.13; b is the bonding force between the bonding piece and the shell, and C is the bonding force between the bonding piece and the naked battery cell. The mass fraction ratio of the carboxylic ester solvent and the additive in the electrolyte in the mixed solvent can adjust the bonding force of the bonding piece and the shell so as to improve the drop test passing rate, meanwhile, the situation that an electrode of a bare cell is torn by impact force caused by drop is avoided, the viscosity of the electrolyte is moderate, the low-temperature and high-temperature performance requirements are met, and the service life of the electrolyte is prolonged. And the cycle capacity retention ratio can be furthest improved.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a battery. Background Art

[0002] Lithium-ion soft-pack batteries are lithium-ion batteries encapsulated in soft packaging materials. The key difference between them and other types of lithium-ion batteries is that they use aluminum-plastic composite film as the packaging material. Compared with batteries with metal shells, they are lighter and thinner, and have great application advantages in electronic products with strict requirements on weight and thickness, such as ultra-thin mobile phones and tablets.

[0003] To improve the pass rate of the drop test for soft-pack lithium-ion batteries, hot-melt double-sided tape is usually applied to one or both sides of the bare cell. The hot-melt double-sided tape on the bare cell melts under temperature and pressure conditions and bonds to the PP surface of the outer aluminum-plastic film. This is used to prevent the cell from moving inside the outer aluminum-plastic film during the drop test, avoiding situations such as electrode folding, short-circuiting of the positive and negative electrodes, or fire in the cell.

[0004] However, currently, the hot-melt double-sided tape of soft-pack lithium-ion batteries is adhered to the bare cell before being placed in the outer film and injected with electrolyte. Subsequently, hot pressing is used to achieve the bonding between the outer film and the hot-melt double-sided tape. Because the hot-melt double-sided tape is adhered to the bare cell in advance, the bonding strength is not easily affected by the electrolyte. However, the hot-melt double-sided tape and the outer film need to come into contact with the electrolyte before hot-pressing, making the bonding strength easily affected by the electrolyte. This poses a risk of the hot-melt double-sided tape and the outer film failing, resulting in a reduced cell pass rate. Furthermore, some hot-melt double-sided tapes have excessive adhesion to the outer film, which can cause the aluminum foil on one side of the bare cell to tear during a drop test, leading to cell capacity degradation. Summary of the Invention

[0005] The present invention provides a battery that utilizes an electrolyte to adjust the adhesive force of an adhesive member on a bare battery cell, thereby improving the drop test pass rate of the battery while ensuring excellent cycle stability and cycle capacity retention of the battery.

[0006] In order to solve the above technical problems, the present invention aims to provide a battery, comprising a bare cell, an adhesive member and a shell, wherein the shell is coated on the outside of the bare cell, and the adhesive member is arranged on one side or two opposite sides of the bare cell and is located between the bare cell and the shell; the bare cell comprises an electrolyte, the electrolyte comprises a lithium salt and a mixed reagent, the mixed reagent comprises a carboxylate solvent with a mass fraction A, an additive with a mass fraction A1 and a carbonate solvent as the balance, and the additive is trimethyl phosphate;

[0007] The battery satisfies the following relationship: 1.7≤(A+A1) / B≤4.7, 45wt%≤A≤60wt%, 2wt%≤A1≤10wt%; CB≥0.13; wherein B is the bonding strength between the bonding member and the shell, in N / mm; C is the bonding strength between the bonding member and the bare battery cell, in N / mm.

[0008] This application controls the mass fraction of the electrolyte carboxylate solvent and the additive in the mixed solvent, and satisfies the formula 1.7≤(A+A1) / B≤4.7, which can adjust the bonding force between the adhesive and the casing. This can not only avoid the bare battery cell from moving inside the casing due to too little bonding force, thereby improving the pass rate of the drop test, but also ensure that the viscosity of the electrolyte is moderate, meeting the performance requirements of low and high temperatures. The additive can improve the cycle stability of the negative electrode interface, and the battery's cycle interface is excellent, meeting the high-temperature cycle performance requirements of the battery. If the carboxylate solvent is too low, the viscosity of the electrolyte will be too high, which will affect the lithium ion transmission rate and SEI film formation. If the carboxylate solvent is too high, the high-temperature cycle performance of the battery will be affected. At the same time, the present application controls the bonding force between the adhesive and the bare battery cell and the shell to satisfy the formula CB≥0.13, which can increase the bonding force difference between the adhesive and the shell and bare battery cell interface, so that the bonding force C value of the bare battery cell interface is 0.13N / mm higher than the bonding force B value of the shell interface. If the bonding force between the adhesive and the bare battery cell is too small, resulting in a too low CB value, even if the battery can successfully pass the drop test, the impact force generated during the drop test cannot be effectively transferred, which can easily cause tearing of the bare battery cell electrode, and ultimately lead to a decay of the battery's cycle capacity.

[0009] As a preferred embodiment, the mass fraction A of the carboxylate solvent in the total amount of the mixed solvent is any one of 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, or any two of the range values.

[0010] As a preferred solution, the battery satisfies the following relationship: 1.7≤(A+A1) / B≤2.5.

[0011] As a preferred solution, the bonding force B between the bonding member and the housing is ≥0.15 N / mm.

[0012] As a preferred solution, the bonding force C between the bonding member and the bare battery core is ≥0.3 N / mm.

[0013] As a preferred embodiment, the carbonate solvent includes at least one of propylene carbonate, ethyl methyl carbonate and dimethyl carbonate.

[0014] As a preferred embodiment, the carboxylate solvent includes at least one of ethyl acetate, propyl propionate and ethyl propionate.

[0015] As a preferred embodiment, the carboxylate solvent comprises ethyl acetate and propyl propionate in a mass ratio of 1:(1-4).

[0016] The carboxylic acid ester solvent used in this application is a compound of polar ethyl acetate and non-polar propyl propionate. The alkyl chains of ethyl acetate are methyl (CH3-) and ethyl (CH3CH2-), which are relatively short, highly polar, and have a large swelling effect on the adhesive. Propionate: The alkyl chains are ethyl (CH3CH2-) and propyl (CH3CH2CH2-), which are relatively long and more complex. It is a non-polar group. Its increased length will dilute the polarity of the molecule. The longer the alkyl chain, the greater the proportion of the non-polar part in the molecule, which will weaken the polar effect of ethyl acetate. Therefore, controlling the proportion of propyl propionate to a high level can reduce the polarity of the overall molecule, thereby weakening the swelling of the adhesive and helping to improve the bonding force.

[0017] As a preferred embodiment, the carboxylate solvent includes ethyl acetate and propyl propionate in a mass ratio of any one of 1:1, 1:2, 1:3, 1:4 or any two of the range values.

[0018] The present application controls the mass ratio of the carboxylic acid ester solvent ethyl acetate and propyl propionate in the electrolyte within the above range, which can adjust the bonding force between the adhesive and the outer shell and the bare battery cell, so that the battery satisfies the formula range of 1.7≤(A+A1) / B≤4.7, thereby achieving the maximum battery cycle capacity retention rate while passing the drop test.

[0019] As a preferred embodiment, the carbonate solvent includes ethyl methyl carbonate and dimethyl carbonate in a mass ratio of 1:(1-4).

[0020] The carbonate solvent in this application is a compound of ethyl methyl carbonate and dimethyl carbonate. Ethyl methyl carbonate is formed by the esterification of carbonic acid with methanol and ethanol. Its substituents are methyl (-CH3) and ethyl (-C2H5), respectively. The molecular structure is asymmetric, so it has strong polarity. The dimethyl carbonate molecule is formed by the esterification of carbonic acid (H2CO3) with methanol (CH3OH). Both substituents are methyl (-CH3). The ester group (-COO-) connects the two methyl groups. The overall structure is symmetrical, so it has weak polarity. By using more dimethyl carbonate to dilute the highly polar ethyl methyl carbonate, the swelling of the adhesive can be reduced and the bonding strength can be improved.

[0021] As a preferred embodiment, the carbonate solvent includes ethyl methyl carbonate and dimethyl carbonate in a mass ratio of any one of 1:1, 1:2, 1:3, 1:4 or any two of the range values.

[0022] As a preferred solution, the adhesive member is a hot melt double-sided adhesive, and the material of the hot melt double-sided adhesive includes at least one of styrene-isoprene-styrene, acrylic resin polymer, polytetrafluoroethylene, polyester, polyimide, polyethylene, and polypropylene.

[0023] As a preferred solution, the hot melt double-sided adhesive is styrene-isoprene-styrene.

[0024] The styrene-isoprene-styrene molecule consists of a polyisoprene (PI) soft segment in the middle and polystyrene (PS) hard segments at both ends. This block structure gives the material both the rigidity of polystyrene and the elasticity of polyisoprene. At room temperature, the PS hard segments aggregate to form physical crosslinking points, restricting the movement of the PI soft segments and giving the material a certain shape and strength. At high temperatures, the physical crosslinking effect of the PS hard segments weakens, and the material can exhibit liquid-like fluidity, making it easier to process. Compared with other materials, it has better processing performance and stronger resistance to electrolyte solvents.

[0025] As a preferred solution, the thickness of the bonding member is 10-100 μm.

[0026] As a preferred solution, the shell is an aluminum-plastic film.

[0027] As a preferred embodiment, the lithium salt is lithium hexafluorophosphate.

[0028] As a preferred solution, the adhesive force B value between the adhesive member and the housing and the adhesive force C value between the adhesive member and the bare battery cell are tested according to the standard of GB / T 2792-2014 "Test method for peel strength of adhesive tapes".

[0029] As a preferred solution, a recess is formed on the surface of the housing close to the adhesive member, and the adhesive member is embedded in the recess.

[0030] As a preferred solution, the bare battery cell further includes a positive electrode sheet, a separator and a negative electrode sheet.

[0031] As a preferred embodiment, the positive electrode sheet includes a positive electrode active material, a positive electrode conductor, and a positive electrode binder in a mass ratio of (90-98): (1-4): (2-6).

[0032] As a preferred embodiment, the positive electrode active material is at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate and lithium manganese oxide.

[0033] As a preferred embodiment, the negative electrode sheet includes a negative electrode active material, a negative electrode conductor, a negative electrode binder, and a thickener in a mass ratio of (92-98):(1-3):(1-5):(1-3).

[0034] As a preferred embodiment, the negative electrode active material is at least one of a carbon-based compound, a silicon-based compound, a titanium-based compound, a tin-based alloy, and a transition metal nitride.

[0035] As a preferred solution, the negative electrode active material is artificial graphite.

[0036] As a preferred solution, the positive electrode binder and the negative electrode binder are each independent and are at least one of polyacrylate, polyvinylidene fluoride, polytetrafluoroethylene, and styrene-butadiene rubber.

[0037] As a preferred embodiment, the positive electrode conductive agent and the negative electrode conductive agent are each independent and are at least one of conductive carbon black, carbon nanotubes, acetylene black, and graphene.

[0038] As a preferred embodiment, the thickener is sodium carboxymethyl cellulose.

[0039] As a preferred solution, the separator is at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, and aramid.

[0040] As a preferred solution, one side or both sides of the diaphragm material are coated with at least one of ceramic, lithium titanium aluminum phosphate, and lithium lanthanum zirconium oxide solid electrolyte.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. The present application controls the mass fraction of the carboxylate solvent and the additive in the mixed solvent in the electrolyte to adjust and increase the adhesion between the adhesive and the shell, which helps to improve the pass rate of the drop test. At the same time, it increases the difference in adhesion between the adhesive and the shell and the bare cell interface, so that the adhesion C value of the bare cell interface is 0.13N / mm higher than the adhesion B value of the shell interface, which can avoid the impact force generated during the drop test from causing tearing of the bare cell electrode, thereby ensuring the cycle stability of the battery.

[0043] 2. The mass fraction range of the carboxylate solvent in the mixed solvent of the present application can ensure that the viscosity of the electrolyte is moderate to meet the performance requirements of low temperature and high temperature. The additive can further improve the negative electrode cycle interface and SEI film formation of the battery, avoid severe lithium plating during the cycle process and cause capacity decay, so as to maintain a high cycle capacity retention rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 : is a schematic diagram of the cross-sectional structure of a battery in an embodiment of the present invention. DETAILED DESCRIPTION

[0045] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0046] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0047] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0048] As used herein:

[0049] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0050] The conjunction "consisting of" excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim, rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0051] In these examples, parts and percentages are by mass unless otherwise indicated.

[0052] "Parts by mass" is a basic unit of measurement that expresses the proportional relationship between the masses of multiple components. One part can represent any unit of mass. For example, if we say that the mass of component A is a parts and the mass of component B is b parts, this means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, we could say that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number representing a multiplication factor). It's important to note that, unlike parts by mass, the sum of the mass of all components is not limited to 100 parts.

[0053] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0054] In the description of the present invention, it should be understood that the terms "up", "down", "left", "right", "top", "bottom", etc., indicating directions or positional relationships, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0055] To further illustrate the present invention, the present invention is described in detail below with reference to the following examples, but these examples should not be construed as limiting the scope of the present invention. Unless otherwise specified, the sources of the raw materials used in the following examples and comparative examples of the present application are commercially available, and the same raw materials were used in parallel experiments.

[0056] Examples 1-12 and Comparative Examples 1-6

[0057] A method for preparing a battery comprises the following steps:

[0058] (1) Preparation of positive electrode sheet: lithium cobalt oxide positive electrode active material, polyvinylidene fluoride (PVDF) binder, and acetylene black conductive agent were mixed in a mass ratio of 95.5:1.8:2.7, N-methylpyrrolidone (NMP) was added, and the mixture was stirred in a vacuum mixer to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was evenly coated on an aluminum foil with a thickness of 10 μm, and after being baked in an oven with 5 different temperature gradients, it was dried in an oven at 120°C for 8 h, and then rolled and cut to obtain a positive electrode sheet;

[0059] (2) Preparation of negative electrode sheet: artificial graphite negative electrode active material, sodium carboxymethyl cellulose (CMC-Na) thickener, styrene-butadiene rubber binder, conductive agent acetylene black conductive agent, and single-walled carbon nanotube (SWCNT) conductive agent were mixed in a mass ratio of 95.3:1.2:1.5:1:1, deionized water was added, and a negative electrode slurry with a solid content of 50 wt% was obtained under the action of a vacuum mixer. The negative electrode slurry was evenly coated on a copper foil with a thickness of 6 μm, dried at a temperature of 85°C for 5 h, and then rolled and slit to obtain a negative electrode sheet;

[0060] (3) in a glove box filled with argon (water <10 ppm, oxygen <1 ppm), a carbonate solvent and a carboxylate solvent are mixed uniformly, lithium hexafluorophosphate and an additive, wherein the additive is trimethyl phosphate or vinylene carbonate, are quickly added to the mixed solution, and stirred uniformly to obtain an electrolyte;

[0061] Wherein, the electrolyte includes a mixed solvent with a mass fraction of 88wt% and 12wt% lithium hexafluorophosphate (LiPF6), the mixed solvent includes a carboxylate solvent with a mass fraction of A, an additive A1 and the remainder of a carbonate solvent, and in the embodiment, A and A1 satisfy the following ranges: 45wt%≤A≤60wt%, 2wt%≤A1≤10wt%, and the A value and A1 value are specifically shown in Table 1 below; the carboxylate solvent includes ethyl acetate (EA) and propyl propionate (PP) in a mass ratio of (0.3-1):1, and the components and mass ratios of the carboxylate solvent are shown in Table 1 below; the carbonate solvent includes ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a mass ratio of (0.3-1):1, and the components and mass ratios of the carbonate solvent are shown in Table 1 below;

[0062] (4) Preparation of lithium-ion battery: The positive electrode sheet, the separator, and the negative electrode sheet are wound to obtain a bare battery cell without liquid injection. The separator is a coated polyethylene separator with a thickness of 8 μm; Figure 1 As shown, a layer of hot-melt double-sided tape was adhered to two opposite sides of the bare cell. The hot-melt double-sided tape was styrene-isoprene-styrene, model 216 from Changhong Polymer Technology Co., Ltd., with a size of 62 mm × 20 mm × 37 μm. The bare cell with the hot-melt double-sided tape was then placed in a punched aluminum-plastic film shell (model DEL40H (III), thickness 113 μm), and the electrolyte prepared in the above Examples 1-12 or Comparative Examples 1-6 was injected at the same time, as shown in Table 1 below. After vacuum packaging, standing, forming, shaping, and sorting processes, a battery with a size of 90 mm × 66 mm × 54 mm was obtained.

[0063] Among them, the bonding force between the hot-melt double-sided adhesive and the aluminum-plastic film of the prepared battery was tested to be B, unit N / mm, and the bonding force between the hot-melt double-sided adhesive and the bare battery cell was tested to be C, unit N / mm, and the embodiment satisfies the following relationship: 1.75≤(A+A1) / B≤4.67, and CB≥0.13.

[0064] Example 13

[0065] A method for preparing a battery, wherein each step and the reagents, equipment, and process parameters used in each step are the same as those in Example 4, except that in step (4), the hot-melt double-sided adhesive is an acrylic resin polymer, model ergo.1665, from Shenzhen Kingsbon Co., Ltd.

[0066] Example 14

[0067] A method for preparing a battery, wherein each step and the reagents, equipment, and process parameters used in each step are the same as those in Example 1, except that in step (4), the hot-melt double-sided adhesive is an acrylic resin polymer, model ergo.1665, from Shenzhen Kingsbon Co., Ltd.

[0068] Comparative Example 7

[0069] A method for preparing a battery, wherein each step and the reagents, equipment, and process parameters used in each step are the same as those in Example 5, except that in step (4), the hot-melt double-sided adhesive is an acrylic resin polymer, model ergo.1665, from Shenzhen Kingsbon Co., Ltd.

[0070] Comparative Example 8

[0071] A method for preparing a battery, wherein each step and the reagents, equipment, and process parameters used in each step are the same as those in Example 6, except that in step (4), the hot-melt double-sided adhesive is an acrylic resin polymer, model ergo.1665, from Shenzhen Kingsbon Co., Ltd.

[0072] Table 1 - Electrolyte parameters and adhesion test results of the battery of the embodiment and the comparative example

[0073]

[0074]

[0075]

[0076] Performance testing

[0077] 1. Adhesion test: refer to the standard of GB / T 2792-2014 "Test method for peel strength of adhesive tape", the test tool is a tensile testing machine, and the auxiliary tools are scissors and spare tape. Specifically, the following steps are included: the lithium-ion battery prepared in the embodiment or comparative example is disassembled in a disassembly room (temperature 25±5°C, humidity ≤10%), and the adhesion between the hot-melt double-sided tape and the aluminum-plastic film is tested as an example. After disassembly, the battery cell needs to retain the bonding area between the hot-melt double-sided tape and the aluminum-plastic film, and a portion of the aluminum-plastic film with a longitudinal length of 5-10 mm is reserved for bonding the spare tape. The spare tape is bonded to the reserved aluminum-plastic film to facilitate clamping by the tensile testing machine. The upper end of the tensile testing machine clamps the aluminum-plastic film and the spare tape, and the lower end clamps the bare battery cell tail body. The tensile testing machine was tested at a speed of 300 mm / min, and the tensile force when moved to a distance of 20 mm-70 mm was counted. The tensile force was divided into 10 mm intervals, and the maximum tensile force of each interval in 5 intervals was taken in N. The average of the maximum tensile force values ​​in the 5 intervals was calculated and then divided by the width W of the hot-melt double-sided adhesive tape in mm. The value was obtained and recorded. The adhesion between the aluminum-plastic film and the hot-melt double-sided adhesive tape obtained by the test was defined as BN / mm; the test method for the adhesion C value between the hot-melt double-sided adhesive tape and the bare battery cell was the same as the test method for the adhesion B value between the hot-melt double-sided adhesive tape and the aluminum-plastic film, except that the aluminum-plastic film and the bare battery cell were correspondingly exchanged during the test process. The test results are shown in Table 2 below.

[0078] 2. Drop test: Prepare a standard micro-drop fixture (VIV-496699 fixture). Before the drop test, install the batteries prepared in each Example or Comparative Example into the fixture and press firmly for 1-2 minutes. Wrap a circle of transparent tape around the fixture to prevent the screws from loosening and falling off. After the glue is allowed to rest for 1 hour, start the drop test. Test 10 batteries in each group. The specific steps are as follows:

[0079] 1) Drop the battery from a height of 10 cm onto a 1 cm thick wooden board;

[0080] 2) Drop times: 20,000 times on each side of the battery with hot-melt double-sided tape, at a drop rate of 15 times / min; 500 times on each of the other four sides, at a drop rate of 40 times / min;

[0081] 3) After standing for 1 hour, the open circuit voltage (OCV) and internal resistance (IMP) are measured. After the test, the battery cell is notified to remove the battery cell for disassembly. The drop test requires compliance with UN38.3 certification, UL certification, CQC certification, and CB certification standards. The statistical drop test pass rate results are shown in Table 1 below.

[0082] 3. 45°C cycle test: The batteries obtained in the examples and comparative examples were placed in a (45±2)°C environment and allowed to stand for 30 minutes. When the battery body reached (55±2)°C, the battery was discharged at a constant current of 0.7C with a cut-off voltage of 3.0V. After the battery was discharged, it was placed for 10 minutes and then charged at a constant current of 0.5C to 4.50V with a cut-off current of 0.05C. The highest discharge capacity of the first three cycles was recorded as the initial capacity Q1. When the cycle reached 500 cycles, the last discharge capacity Q2 of the battery was recorded. The capacity retention rate (%) = Q2 / Q1×100%. The capacity retention rate test results are shown in Table 2 below.

[0083] Table 2 - Performance test results of the present application examples and comparative examples

[0084]

[0085]

[0086] As shown in Table 2, Examples 1-6 of the present application control the carboxylic acid ester solvent in the electrolyte to account for the total mass fraction of the mixed solvent in the range of 45wt%≤A≤60wt%, and the additive to account for the total mass fraction of the mixed solvent in the range of 2wt%≤A1≤10wt%, thereby improving the high temperature performance of the battery cell and the lithium ion transmission rate, thereby making the cycle performance of the battery cell excellent; the bonding force B value of the hot-melt double-sided adhesive and the aluminum-plastic film satisfies the formula range of 1.75≤(A+A1) / B≤4.67, which can ensure that the bonding force between the hot-melt double-sided adhesive and the bare battery cell and the aluminum-plastic film meets the requirements of the drop test, avoiding the bare battery cell from moving in the outer casing due to too little bonding force, and the viscosity of the electrolyte is moderate, meeting the performance requirements of low and high temperatures, and the battery has an excellent cycle interface. At the same time, controlling the bonding strength between the hot-melt double-sided adhesive and the bare battery cell and the aluminum-plastic film to satisfy the formula CB≥0.13 can avoid the bonding strength between the hot-melt double-sided adhesive and the bare battery cell being too weak. If the bonding strength between the hot-melt double-sided adhesive and the interface between the bare battery cell and the aluminum-plastic film is too small, it will cause the electrode to tear during the drop test, causing battery capacity degradation, thereby maximizing the drop test pass rate while maintaining a high cycle capacity retention rate.

[0087] Compared with Examples 1 and 4-6, the carboxylate solvent in the electrolyte of Comparative Example 1 accounts for 40wt% of the solvent mass fraction A. The proportion of carboxylate solvent is too small, and the increased viscosity will affect SEI film formation, resulting in lithium precipitation at the interface and slowing down the mobility of lithium ions. In addition, too little carbonate solvent reduces the ionic conductivity and intensifies the polarization phenomenon, which reduces the battery cycle capacity retention rate. In addition, too little carboxylate solvent will lead to enhanced adhesion between the hot-melt double-sided adhesive and the aluminum-plastic film. Although the pass rate during the drop test is high, the difference in adhesion between the hot-melt double-sided adhesive and the interface of the bare battery cell and the interface of the aluminum-plastic film is too small. The impact force generated during the drop process cannot be effectively transferred, resulting in the torn electrode on one side of the bare battery cell causing capacity decay during the cycle, and the capacity retention rate is further reduced. In Comparative Example 2, the carboxylate solvent accounts for 65wt% of the total mass fraction A of the mixed solvent in the electrolyte. The carboxylate solvent accounts for too much, and the boiling point of the carboxylate solvent itself is low. Too much will lead to poor high-temperature performance of the battery and affect the circulation interface. In addition, too much carboxylate solvent will cause the bonding force of the hot-melt double-sided tape to be too weak, and the bonding interface between the hot-melt double-sided tape and the aluminum-plastic film will fail, resulting in a reduced pass rate during the drop test.

[0088] Compared to Example 1, no additives were added to the electrolyte of Comparative Example 3. Although the drop test pass rate of the battery cell was improved, the negative electrode interface stability deteriorated, resulting in a significant decrease in the high-temperature cycle capacity retention rate of the battery cell. The excessive content of additives in the electrolyte of Comparative Example 4 will lead to a decline in ion conduction and rate performance, excessive thickening of the SEI film and increased interface impedance, and a decrease in the cycle capacity retention rate; and it will affect the adhesion between the hot-melt double-sided adhesive and the bare battery cell and the aluminum-plastic film, resulting in a decrease in the drop test pass rate of the battery cell. In addition, Comparative Example 6 uses vinylene carbonate as an additive, which will decompose and consume active lithium, resulting in a loss of reversible capacity. Moreover, a large amount of vinylene carbonate will also cause the SEI film to thicken, the viscosity of the electrolyte to increase, hinder the transmission of ions, and affect the cycle performance of the battery cell.

[0089] Compared with Example 1, the mass fraction of the carboxylic acid ester solvent and the additive in the electrolyte of Comparative Example 5 in the total mass fraction of the mixed solvent satisfies the range of 45wt%≤A≤60wt% and 2wt%≤A1≤10wt%, but the bonding strength of the hot-melt double-sided adhesive in the battery to the bare battery cell and the aluminum-plastic film exceeds the range of formula CB≥0.13, indicating that the bonding strength between the hot-melt double-sided adhesive and the interface between the bare battery cell and the aluminum-plastic film is too small. This will result in the bonding strength of the hot-melt double-sided adhesive to the bare battery cell not being able to significantly exceed its bonding strength to the aluminum-plastic film. The impact force generated by the drop test cannot be effectively transferred, and the drop test process is likely to cause tearing of the electrode, thereby causing the battery's cycle capacity to decay.

[0090] Compared with Examples 1 and 4-6, the hot-melt double-sided adhesives in Examples 13-14 and Comparative Examples 7-8 use acrylic resin polymers. The adhesive force of the acrylic resin polymer caused by swelling of the carboxylic acid ester solvent fluctuates greatly, resulting in low adhesive force to the aluminum-plastic film. Only when the mass fraction of the carboxylic acid ester solvent in the mixed solvent is less than 50wt%, can it have sufficiently high adhesive force. When the mass fraction of the carboxylic acid ester solvent in the mixed solvent is more than 55wt%, the adhesive force B value will be greatly reduced, thereby significantly reducing the pass rate of the battery drop test.

[0091] The specific embodiments described above further illustrate the objectives, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A battery, characterized in that: The invention comprises a bare cell, an adhesive and a shell, wherein the shell is coated on the outside of the bare cell, and the adhesive is arranged on one side or two opposite sides of the bare cell and is located between the bare cell and the shell; the bare cell comprises an electrolyte, wherein the electrolyte comprises a lithium salt and a mixed solvent, wherein the mixed solvent comprises a carboxylate solvent with a mass fraction A, an additive with a mass fraction A1 and a carbonate solvent as the balance, wherein the additive is trimethyl phosphate; The battery satisfies the following relationship: 1.7≤(A+A1) / B≤4.7, 45wt%≤A≤60wt%, 2wt%≤A1≤10wt%; CB≥0.13; wherein B is the bonding strength between the bonding member and the shell, in N / mm; C is the bonding strength between the bonding member and the bare battery cell, in N / mm.

2. The battery according to claim 1, wherein The battery satisfies the following relationship: 1.7≤(A+A1) / B≤2.

5.

3. The battery according to claim 1, wherein The bonding force B between the bonding member and the housing is ≥ 0.15 N / mm; And / or, the bonding force C between the adhesive member and the bare battery cell is ≥0.3 N / mm.

4. The battery according to claim 1, wherein The carbonate solvent includes at least one of propylene carbonate, ethyl methyl carbonate and dimethyl carbonate; And / or, the carboxylate solvent includes at least one of ethyl acetate, propyl propionate and ethyl propionate.

5. The battery according to claim 4, wherein The carboxylate solvent includes ethyl acetate and propyl propionate in a mass ratio of 1:(1-4).

6. The battery according to claim 4, wherein The carbonate solvent includes ethyl methyl carbonate and dimethyl carbonate in a mass ratio of 1:(1-4).

7. The battery according to claim 1, wherein The adhesive is a hot-melt double-sided adhesive. The material of the hot-melt double-sided adhesive includes at least one of styrene-isoprene-styrene, acrylic resin polymer, polytetrafluoroethylene, polyester, polyimide, polyethylene, and polypropylene.

8. The battery according to claim 7, wherein The shell is an aluminum-plastic film; And / or, the material of the hot-melt double-sided adhesive includes styrene-isoprene-styrene.

9. The battery according to claim 1, wherein The thickness of the bonding member is 10-100 μm.

10. The battery according to claim 1, wherein A recess is formed on the surface of the shell close to the bonding piece, and the bonding piece is embedded in the recess.

Images