CN115832444A - Secondary battery, battery module, battery pack, and electric device - Google Patents
Secondary battery, battery module, battery pack, and electric device Download PDFInfo
- Publication number
- CN115832444A CN115832444A CN202210607453.5A CN202210607453A CN115832444A CN 115832444 A CN115832444 A CN 115832444A CN 202210607453 A CN202210607453 A CN 202210607453A CN 115832444 A CN115832444 A CN 115832444A
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- Prior art keywords
- electrolyte
- secondary battery
- battery
- film layer
- linear
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Images
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
The application provides a secondary battery, a battery module, a battery pack, and an electric device. The secondary battery comprises a negative pole piece and electrolyte, wherein the negative pole piece comprises a negative pole current collector and a negative pole film layer formed on the negative pole current collector, the negative pole film layer comprises a binder, the electrolyte contains linear carbonate and linear carboxylate, and the electrolyte is used for dissolving the electrolyteWherein the sum of the mass percentage of the linear carbonate and the mass percentage of the linear carboxylate is A%, and the content of the binder per unit area of the negative electrode film layer is S mg/dm 2 S and A satisfy the following relation: s is more than or equal to 0.40A and less than or equal to 0.70A.
Description
Technical Field
The present application relates to the field of secondary battery technology, and in particular, to a secondary battery, a battery module, a battery pack, and an electric device.
Background
In recent years, secondary batteries have been widely used in energy storage power systems such as hydraulic power, thermal power, wind power, and solar power stations, and in various fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.
As the development of secondary batteries has been greatly advanced, higher requirements are also placed on the quick charge performance, the cycle performance, the safety performance, and the like of the secondary batteries.
Therefore, a secondary battery having both good quick charge performance and cycle life is desired.
Disclosure of Invention
In view of the problems of the prior art, an object of the present invention is to provide a secondary battery that can achieve both good quick charge performance and cycle life, and a battery module, a battery pack, and an electric device using the secondary battery.
In order to achieve the above object, a first aspect of the present application provides a secondary battery comprising a negative electrode tab and an electrolyte,
the negative pole piece comprises the negative pole current collector and a negative pole film layer formed on the negative pole current collector, the negative pole film layer comprises a binder,
the electrolyte contains a linear carbonate and a linear carboxylate,
the sum of the mass percentage of the linear carbonate and the mass percentage of the linear carboxylate in the electrolyte is defined as A%, and the content of the binder per unit area of the negative electrode film layer is defined as S mg/dm 2 S and A satisfy the following relation:
0.40A≤S≤0.70A。
in the present application, the rapid charging performance and cycle life of the secondary battery can be both considered by adjusting the relationship between the total content of the linear carbonate and the linear carboxylate in the electrolyte and the binder content per unit area of the negative electrode film layer.
In any embodiment, S and a may satisfy the following relationship: s is more than or equal to 0.40A and less than or equal to 0.60A.
Therefore, better balance between the high conductivity of the electrolyte and the low swelling property of the binder can be further ensured, and the quick charge performance and the cycle life of the secondary battery are better.
In any embodiment, the linear carbonate may be present in the electrolyte in an amount of 10 to 50% by mass.
Therefore, the higher conductivity of the electrolyte can be obtained, the liquid phase transmission dynamic performance of ions is improved, the negative electrode lithium separation in the quick charge process and the long-term use process is avoided, the quick charge performance and the cycle life can be improved, and in addition, the oxidation potential of the linear carbonate is higher (compared with that of the cyclic carbonate), the electrochemical window of the electrolyte is improved, the side reaction of a negative electrode/electrolyte interface is reduced, and the quick charge performance and the cycle life of the secondary battery are improved.
In any embodiment, the linear carboxylic acid ester may be contained in the electrolyte in an amount of 10 to 20% by mass.
The linear carboxylic ester has a low viscosity, and by setting the content of the linear carboxylic ester to the above range, the liquid phase transport resistance of ions can be further reduced, and the quick charge performance and cycle performance of the secondary battery can be improved.
In any embodiment, the sum of the mass percentage of the linear carbonate and the mass percentage of the linear carboxylate in the electrolyte may be: 20 percent to 70 percent of A percent.
Therefore, under the combined action of the linear carbonate and the linear carboxylate, the viscosity of the electrolyte is obviously reduced, the conductivity is obviously improved, the dynamic performance is better, the electrochemical stability is good, and the secondary battery can be further ensured to have better circulation stability.
In any embodiment, the content of the binder per unit area of the negative electrode film layer may be 8 to 60mg/dm 2 。
Therefore, the use amount of the binder of the negative electrode film layer is controlled, so that the negative electrode film layer can be prevented from falling off due to expansion and contraction of the negative electrode piece in the cycle use process, and the cycle life of the battery is prolonged.
In any embodiment, the electrolyte may have a conductivity of 9 to 15mS/cm.
Therefore, the quick charge performance and the long-term cycle life of the battery can be ensured by controlling the conductivity of the electrolyte within a certain range.
A second aspect of the present application provides a battery module including the secondary battery of the first aspect of the present application.
A third aspect of the present application provides a battery pack including the battery module of the second aspect of the present application.
A fourth aspect of the present application provides an electric device including the secondary battery of the first aspect of the present application, the battery module of the second aspect of the present application, or the battery pack of the third aspect of the present application.
Effects of the invention
In the secondary battery, the relation between the total content of the linear carboxylic ester and the linear carbonic ester in the electrolyte and the content of the binder on the unit area of the negative electrode film layer is adjusted, so that the viscosity of the electrolyte is suitable for the liquid phase transmission dynamic performance of ions, the charging rate performance is improved, the stability of the negative electrode plate in the recycling process can be ensured, and the quick charging performance and the cycle life of the secondary battery are both considered. Specifically, as a solvent in the electrolytic solution, linear carboxylic acid esters and linear carboxylic acid esters have a smaller molecular volume than cyclic carboxylic acid esters and cyclic carboxylic acid esters, and the viscosity of the electrolytic solution can be reduced. Therefore, in the present application, in order to adapt the viscosity of the electrolyte to the liquid phase transport kinetics of ions, a linear carboxylic acid ester and a linear carbonate are added to the electrolyte. However, linear carboxylic ester and linear carbonate have a certain swelling effect on the binder in the negative electrode film layer, and when the content of the linear carboxylic ester and the linear carbonate reaches a certain degree, the bonding performance of the binder may be reduced, so that the negative electrode film layer falls off, and the quick charge performance and the cycle life of the secondary battery are seriously affected. Through a large number of experiments, the inventors of the present application found that: when the sum of the contents of the linear carbonate and the linear carboxylate in the electrolyte and the content of the binder on the unit area of the negative electrode film layer satisfy the relationship that S is more than or equal to 0.40A and less than or equal to 0.70A, the secondary battery can obtain higher conductivity and good charge rate performance of the electrolyte, and can not cause the reduction of the adhesive force of the negative electrode film layer, thereby obtaining the secondary battery which has both quick charge performance and cycle life.
Drawings
Fig. 1 is a schematic view of a secondary battery according to an embodiment of the present application.
Fig. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in fig. 1.
Fig. 3 is a schematic view of a battery module according to an embodiment of the present application.
Fig. 4 is a schematic diagram of a battery pack according to an embodiment of the present application.
Fig. 5 is an exploded view of the battery pack according to the embodiment of the present application shown in fig. 4.
Fig. 6 is a schematic diagram of an electric device in which a secondary battery according to an embodiment of the present application is used as a power source.
Description of reference numerals:
1: a battery pack; 2: an upper box body; 3: a lower box body; 4: a battery module; 5: a secondary battery; 51: a housing; 52: an electrode assembly; 53: a cap assembly.
Detailed Description
Hereinafter, embodiments specifically disclosing the secondary battery, the battery module, the battery pack, and the electric device according to the present application will be described in detail with reference to the drawings as appropriate. But a detailed description thereof will be omitted. For example, detailed descriptions of already known matters and repetitive descriptions of actually the same configurations may be omitted. This is to avoid unnecessarily obscuring the following description, and to facilitate understanding by those skilled in the art. The drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.
As disclosed herein, a "range" is defined in terms of lower and upper limits, with a given range being defined by the selection of one lower limit and one upper limit, which define the boundaries of the particular range. Ranges defined in this manner may or may not include endpoints and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Further, if the minimum range values of 1 and 2 are listed, and if the maximum range values of 3,4 and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In this application, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is only a shorthand representation of the combination of these numbers. In addition, when a parameter is an integer of 2 or more, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, or the like.
All embodiments and alternative embodiments of the present application may be combined with each other to form new solutions, if not specifically stated.
All technical and optional features of the present application may be combined with each other to form new solutions, if not otherwise specified.
All steps of the present application may be performed sequentially or randomly, preferably sequentially, if not specifically stated. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, and may also comprise steps (b) and (a) performed sequentially. For example, reference to the process further comprising step (c) means that step (c) may be added to the process in any order, for example, the process may comprise steps (a), (b) and (c), may also comprise steps (a), (c) and (b), may also comprise steps (c), (a) and (b), etc.
The terms "comprises" and "comprising" as used herein mean either open or closed unless otherwise specified. For example, the terms "comprising" and "comprises" may mean that other components not listed may also be included or included, or that only listed components may be included or included.
In this application, the term "or" is inclusive, if not otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, either of the following conditions satisfies the condition "a or B": a is true (or present) and B is false (or not present); a is false (or not present) and B is true (or present); or both a and B are true (or present).
The application provides a secondary battery, a battery module, a battery pack and an electric device. The secondary battery, the battery module, the battery pack, and the electric device according to the present invention will be described below with reference to the drawings as appropriate.
Secondary battery
As the pace of life gets faster, the quick charge performance is a matter that must be considered in addition to a strong demand for the cycle life of the secondary battery. In order to improve the quick charge performance, it is necessary to improve the liquid phase transport ability of ions in the secondary battery, and a low viscosity solvent is generally added to improve the transport speed of ions and to improve the charge rate performance, thereby achieving the quick charge performance. However, the inventors of the present application have found that the polarity of the low-viscosity solvent is equivalent to the polarity of the binder in the negative electrode film layer, and the low-viscosity solvent easily enters the inside of the binder according to the principle of similar compatibility, so that the binder swells to reduce the adhesive force, and the negative electrode film layer falls off from the negative electrode current collector, thereby seriously affecting the cycle life of the secondary battery.
Therefore, the secondary battery of the related art still needs to be improved in terms of ensuring a low viscosity of the electrolyte while not affecting the adhesion stability of the negative electrode film layer and the negative electrode current collector. The inventors of the present application have conducted extensive studies and have provided the following secondary battery. The secondary battery is improved in the aspect of ensuring the low viscosity of the electrolyte and not influencing the bonding stability of the negative electrode film layer and the negative electrode current collector, so that the good quick charging performance and the good cycle life are both considered.
One embodiment of the present application provides a secondary battery including a negative electrode tab and an electrolyte,
the negative pole piece comprises a negative pole current collector and a negative pole film layer formed on the negative pole current collector, the negative pole film layer comprises a binder,
the electrolyte contains a linear carbonate and a linear carboxylate,
the sum of the mass percentage of the linear carbonate and the mass percentage of the linear carboxylate in the electrolyte is defined as A%, and the content of the binder per unit area of the negative electrode film layer is defined as S mg/dm 2 S and A satisfy the following relation:
0.4A≤S≤0.7A。
although the mechanism is not clear, the applicant has surprisingly found that: by adjusting the relationship between the total content of the linear carbonate and the linear carboxylate in the electrolyte and the content of the binder per unit area of the negative electrode film layer, the quick charge performance and the cycle life of the secondary battery can be both considered.
When the relationship between the total content of the linear carbonate and the linear carboxylate in the electrolyte and the content of the binder in the unit area of the negative electrode film layer is 0.4a > -s, due to the principle of similar intermiscibility, the binder in the negative electrode film layer of the negative electrode plate swells, so that the negative electrode film layer is separated from the negative electrode current collector, and the cycle life is reduced; when the relationship between the total content of linear carbonate and linear carboxylate in the electrolyte and the content of the binder per unit area of the negative electrode film layer is 0.7a < -s, too much binder in the negative electrode film layer results in a significant decrease in conductivity of the negative electrode sheet and an increase in resistance of the negative electrode sheet, since the binder itself is not conductive, resulting in a decrease in the quick charge performance of the battery. The relationship between the total content of the linear carbonate and the linear carboxylate in the electrolyte and the content of the binder per unit area of the negative electrode film layer may be 0.40A. Ltoreq. S.ltoreq.0.60A, and preferably 0.50A. Ltoreq. S.ltoreq.0.60A. Therefore, the quick charge performance and the cycle life of the secondary battery can be further considered.
The secondary battery of the present application may be a lithium ion secondary battery or the like. The secondary battery of the present application may further include a positive electrode sheet and a separator. In the process of charging and discharging the battery, active ions are embedded and separated back and forth between the positive pole piece and the negative pole piece. The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The diaphragm is arranged between the positive pole piece and the negative pole piece, mainly plays a role in preventing the short circuit of the positive pole and the negative pole, and can enable ions to pass through. Each constituent element of the secondary battery will be described in detail below.
[ Positive electrode sheet ]
The positive electrode plate can include a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. As an example, the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two surfaces opposite to the positive electrode current collector.
The positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum 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 base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a polymer material base material (e.g., polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
The positive electrode film layer includes a positive electrode active material. The positive active material includes, but is not limited to, lithium cobaltate, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel type lithium manganate, spinel type lithium nickel manganate, lithium titanate, and the like. One or more of these may be used as the positive electrode active material.
The positive electrode film layer may also optionally include a binder. However, the kind of the binder is not particularly limited, and those skilled in the art can select the binder according to actual needs. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluoroacrylate resin.
The positive electrode film layer may also optionally include a conductive agent. However, the kind of the conductive agent is not particularly limited, and those skilled in the art can select the conductive agent according to actual needs. As an example, the conductive agent for the cathode film layer may be one or more selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
The preparation of the positive electrode sheet may be performed according to methods known in the art. As an example, a positive electrode active material, a conductive agent, and a binder may be dispersed in a solvent (e.g., N-methylpyrrolidone (NMP)) to form a uniform positive electrode slurry; and coating the positive electrode slurry on a positive electrode current collector, and drying, cold pressing and the like to obtain the positive electrode piece.
[ negative electrode Pole piece ]
The negative electrode tab may include a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material and a binder. As an example, the negative electrode current collector has two surfaces opposite in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two surfaces opposite to the negative electrode current collector.
In the secondary battery of the present application, the anode active material may use an anode active material commonly used in the art for preparing an anode of a secondary battery. As the negative electrode active material, artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate, and the like can be cited. The silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds (e.g., silica), silicon carbon composites, silicon nitrogen composites, and silicon alloys. The tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys.
The negative electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of a polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a polymer material base material (e.g., polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
In the secondary battery of the present application, the negative electrode film layer may include a negative electrode active material, a binder, an optional conductive agent, and other optional auxiliary agents, and is generally formed by coating the negative electrode film layer with a slurry and drying. The slurry for the negative electrode film layer is generally formed by dispersing a negative electrode active material, a binder, and optionally a conductive agent and the like in a solvent and uniformly stirring. The solvent may be N-methylpyrrolidone (NMP) or deionized water.
The binder can be selected from more than one of styrene butadiene rubber, polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile, acrylonitrile multipolymer, polyvinyl alcohol, xanthan gum, arabic gum, sodium alginate and sodium carboxymethylcellulose. Because the polarity of the linear carbonate and the linear carboxylate in the electrolyte is closer to that of the binder in the negative electrode film layer, the binder with the polarity which is greatly different from that of the linear carbonate and the linear carboxylate is selected as much as possible when the binder is selected, so that the swelling effect of the binder caused by the close polarity is reduced. From the above viewpoint, styrene-butadiene rubber, sodium carboxymethylcellulose, and polyvinylidene fluoride are preferable as the binder. That is, by selecting such a binder, better stability can be obtained, thereby ensuring cycle stability of the secondary battery.
In some embodiments, the content of the binder per unit area of the negative electrode film layer may be 8 to 60mg/dm 2 . The main functions of the binder are to enhance the acting force between the negative active materials and to increase the adhesive force between the negative film layer and the negative current collector. When it is a negative electrodeThe content of binder per unit area of the film layer is too low, e.g. below 8mg/dm 2 During the process, the production of effective bonding effect is not facilitated, the bonding force between the negative active materials is poor, the bonding force between the negative film layer and the negative current collector is also poor, the phenomena of demoulding and the like easily occur, the stability of the negative pole piece in the recycling process is poor, and the cycle performance of the battery is obviously reduced. When the content of the binder per unit area of the negative electrode film layer is too high, for example, more than 60mg/dm 2 In the case of a lithium ion secondary battery, too much binder (usually, the binder is not conductive or has low conductivity) reduces the conductivity of the negative electrode sheet, which causes the sheet resistance of the negative electrode sheet to increase, thereby reducing the charge rate performance of the battery. The content of the binder in the unit area of the negative electrode film layer is in the range, so that the stability of the negative electrode pole piece in the recycling process can be better ensured, and the charging rate performance of the battery can be better ensured not to be reduced. From the viewpoint of further obtaining the above-described effects, the content of the binder per unit area of the negative electrode film layer is preferably 10 to 45mg/dm 2 More preferably 20 to 42mg/dm 2 。
As an example, the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
As an example, the adjuvant optionally includes a thickener.
The negative electrode sheet can be prepared according to methods known in the art. As an example, the negative electrode active material, the conductive agent, the binder, and any other components may be dispersed in a solvent, such as N-methylpyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry; coating the slurry on at least one surface of a negative current collector by a conventional coating process, and drying, cold pressing and other working procedures to obtain the negative pole piece.
[ electrolyte ]
The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The electrolyte may include an electrolyte salt and a solvent.
As an example, the electrolyte salt may be selected from hexafluoroLithium phosphate (LiPF) 6 ) Lithium tetrafluoroborate (LiBF) 4 ) Lithium perchlorate (LiClO) 4 ) Lithium hexafluoroarsenate (LiAsF) 6 ) Lithium bis (fluorosulfonylimide) (LiFSI), lithium bis (trifluoromethanesulfonylimide) (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalato borate (LiDFOB), lithium dioxaoxalato borate (LiBOB), lithium difluorophosphates (LiPO) 2 F 2 ) One or more of lithium difluorooxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP). Among them, lithium hexafluorophosphate (LiPF) 6 ) And lithium bis (fluorosulfonyl) imide (LiFSI) has good solubility, suitable ionic conductivity, suitable dissociation constant, good oxidation resistance, good thermal stability, and thus lithium hexafluorophosphate (LiPF) is preferred 6 ) And lithium bis (fluorosulfonyl) imide (LiFSI) as an electrolyte salt.
In some embodiments, the concentration of the electrolyte salt in the electrolyte solution may be selected to be 0.8M to 1.5M. When the concentration of the electrolyte salt is too low, for example, less than 0.8M, it is not favorable for achieving the required energy density of the battery, and when the concentration of the electrolyte salt is too high, for example, more than 1.5M, the battery production cost is too high, and lithium deposition is easily formed on the electrode tab, deteriorating the stability of the battery.
In the present application, the solvent in the electrolyte includes a linear carbonate and a linear carboxylate.
In some embodiments, the linear carbonate may be selected from at least one of dimethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, propyl methyl carbonate, diethyl carbonate, and propyl ethyl carbonate. The linear carbonate has a linear alkane structure, so that the viscosity of the electrolyte can be reduced, and the effect of reducing the viscosity is more obvious as the carbon chain is shorter. Dimethyl carbonate has a relatively short carbon chain structure, so that the viscosity reduction effect of dimethyl carbonate is considered to be relatively obvious.
In some embodiments, the linear carboxylic acid ester may be selected from at least one of methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, and ethyl butyrate. Like linear carbonates, linear carboxylates also have the characteristic that the shorter the carbon chain, the more pronounced the reduction in viscosity. However, ethyl acetate is preferred because its boiling point is higher than that of methyl formate and ethyl formate, so that the liquid temperature range of the solvent is wide.
In some embodiments, the linear carbonate may be present in the electrolyte in an amount of 10% to 50% by mass. The linear carbonate has an effect of reducing the viscosity of the electrolyte, and when the content of the linear carbonate is too low, for example, less than 10%, the decrease in the viscosity of the solvent is small, the conductivity of the secondary battery is low, which is not favorable for satisfying the requirement of the ion kinetic diffusion performance, and the quick charge performance of the secondary battery is poor. When the content of the linear carbonate is too high, for example, higher than 50%, the viscosity of the solvent is obviously reduced, but the dielectric constant of the electrolyte is also obviously reduced, the linear carbonate and the binder in the negative electrode film layer are more easily mutually soluble, so that the binder is subjected to an obvious swelling reaction, the retention rate of the cycle capacity of the battery is reduced, and the service life of the battery is influenced. And when the content of the linear carbonate is too high, the flash point of the electrolyte is obviously reduced, and the use safety of the battery cannot be effectively guaranteed due to the obvious temperature rise of the battery in the use process and the low flash point of the solvent. From the viewpoint of further obtaining the above-described effects, the mass percentage of the linear carbonate in the electrolyte solution is preferably 20% to 40%, more preferably 25% to 40%.
In some embodiments, the linear carboxylate in the electrolyte may be 10% to 20% by mass. The linear carboxylic ester has lower viscosity and freezing point and smaller surface tension compared with the linear carbonic ester, and when the linear carboxylic ester is used as a solvent of the electrolyte, the liquid temperature range of the electrolyte is wider, and the low-temperature performance of the battery is better. When the content of the linear carboxylate is too low, for example, less than 10%, the decrease of the viscosity of the solvent is small, the conductivity of the secondary battery is low, which is not favorable for satisfying the requirement of the ion kinetic diffusion performance, and the quick charge performance of the battery is poor. When the content of the linear carboxylate is too high, for example, more than 20%, the viscosity of the electrolyte is significantly reduced, but the negative electrode sheet structure of the battery is damaged due to swelling of the binder due to the compatibility between the linear carboxylate and the binder, and thus the capacity of the battery is significantly reduced after recycling. Meanwhile, the freezing point of the electrolyte is reduced due to the increase of the content of the linear carboxylic ester, and the low-temperature discharge capacity is reduced, so that the electrolyte is not suitable for adding excessive linear carboxylic ester. From the viewpoint of further obtaining the above-described effects, the mass percentage of the linear carboxylic acid ester in the electrolyte is preferably 15% to 20%.
In some embodiments, the sum of the mass percent of linear carbonate and the mass percent of linear carboxylate in the electrolyte may be 20% to A% to 70%. As described above, under the combined action of the linear carbonate and the linear carboxylate, the viscosity of the electrolyte is significantly reduced, so that the electrolyte has better dynamic properties. However, when the sum of the mass percentage of the linear carbonate and the mass percentage of the linear carboxylate in the electrolyte is too low, for example, less than 20%, it is not favorable to ensure that the overall viscosity of the electrolyte meets the requirement of the ion-kinetic diffusion performance. When the sum of the mass percent of the linear carbonate and the mass percent of the linear carboxylate in the electrolyte is too high, for example, higher than 70%, the interaction with the binder is obvious, so that the binder on the negative pole piece undergoes a swelling reaction, the cycle retention rate of the battery is reduced, and the flash point and the freezing point of the electrolyte are also reduced, thereby affecting the use safety of the battery. From the viewpoint of further obtaining the above-described effects, the sum of the mass percentage of the linear carbonate and the mass percentage of the linear carboxylate in the electrolyte is preferably 30% to 60%.
In addition to the above-mentioned linear carbonates and linear carboxylic esters, a certain amount of cyclic carbonates may be added to the solvent system of the electrolyte. The cyclic carbonate can improve the flash point and the boiling point of the electrolyte and increase the liquid temperature range. The mass percentage of the cyclic carbonate in the electrolyte may be 10% to 50%. When the content of the cyclic carbonate is too low, for example, less than 10%, the flash point and boiling point of the electrolyte are low, and the liquid temperature range is narrow. When the cyclic carbonate content is too high, for example, more than 50%, the viscosity of the solvent increases and the kinetic conductivity of the ions is affected. The kind of the cyclic carbonate is not particularly limited, and may be selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, and fluoroethylene carbonate. From the viewpoint of further obtaining the above-described effects, the mass percentage of the cyclic carbonate in the electrolyte solution is preferably 15% to 30%.
In addition, the electrolyte can also contain solvents such as gamma-butyrolactone and tetrahydrofuran, and by adding an organic reagent with stable chemical performance and strong solubility as the solvent, the chemical stability of the electrolyte can be improved, and the compatibility with electrode materials can be improved. However, since ethers have poor oxidation resistance and are easily oxidized and decomposed at a low potential, the amount of the ethers to be added is generally small, and the mass percentage of γ -butyrolactone or tetrahydrofuran in the electrolyte is preferably 5% to 10%.
In some embodiments, additives are also optionally included in the electrolyte. For example, a negative electrode film-forming additive, a positive electrode film-forming additive, an additive for improving the overcharge performance of the battery, an additive for improving the high-temperature performance of the battery, an additive for improving the low-temperature performance of the battery, and the like may be included in the electrolyte. Specific examples thereof include Vinylene Carbonate (VC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), 1,3-Propanesultone (PS), lithium difluorobis (oxalato) phosphate (LiDFOP), lithium difluorooxalato borate (LiDFOB), lithium bis (oxalato) borate (LiBOB), and lithium difluorophosphate (LiPO) 2 F 2 ) And the like.
In some embodiments, the conductivity of the electrolyte may be 9 to 15mS/cm. The conductivity of the electrolyte is affected not only by the viscosity of the solvent but also by the diffusion kinetics of the ions themselves. The conductivity of the electrolyte has a direct influence on the fast charge performance and the charge rate performance of the battery. When the conductivity of the electrolyte is less than 9mS/cm, the quick charge performance and charge rate performance of the battery become low, and the energy density decreases. When the conductivity of the electrolyte is higher than 15mS/cm, the battery is easy to generate a large amount of heat in the recycling process, obvious temperature rise is caused, the use safety of the battery is reduced, and the quick charging performance is also obviously reduced. The conductivity of the electrolyte is preferably 10 to 14mS/cm.
[ separator ]
The diaphragm separates positive pole piece and negative pole piece, prevents that the battery is inside to take place the short circuit, makes active ion can pass the diaphragm and move between the positive negative pole simultaneously. In the secondary battery of the present application, the kind of the separator is not particularly limited, and any known separator having a porous structure with good chemical stability and mechanical stability may be selected.
In some embodiments, the material of the separator may be one or more selected from the group consisting of a glass fiber film, a non-woven fabric film, a Polyethylene (PE) film, a polypropylene (PP) film, a polyvinylidene fluoride film, and a multi-layer composite film including one or more of them. The separator may be a single-layer separator or a multi-layer composite separator, and is not particularly limited. When the separator is a multilayer composite separator, the materials of the respective layers may be the same or different, and are not particularly limited.
In some embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.
In some embodiments, the secondary battery may include an exterior package. The exterior package may be used to enclose the electrode assembly and the electrolyte as described above.
In some embodiments, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like. The outer package of the secondary battery may also be a pouch, such as a pouch-type pouch. The material of the soft bag may be plastic, and examples of the plastic include polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), and the like.
The shape of the secondary battery is not particularly limited, and may be a cylindrical shape, a square shape, or any other arbitrary shape. For example, fig. 1 is a secondary battery 5 of a square structure as an example.
In some embodiments, referring to fig. 2, the overpack may include a housing 51 and a cap assembly 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose to form an accommodating cavity. The housing 51 has an opening communicating with the accommodating chamber, and the top cover assembly 53 can cover the opening to close the accommodating chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is enclosed within the receiving cavity. The electrolyte is impregnated into the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 may be one or more, and those skilled in the art can select them according to the actual needs.
Battery module
In some embodiments, the secondary batteries may be assembled into a battery module, and the number of the secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.
Fig. 3 is a battery module 4 as an example. Referring to fig. 3, in the battery module 4, a plurality of secondary batteries 5 may be arranged in series along the longitudinal direction of the battery module 4. Of course, the arrangement may be in any other manner. The plurality of secondary batteries 5 may be further fixed by a fastener.
Alternatively, the battery module 4 may further include a case having an accommodation space in which the plurality of secondary batteries 5 are accommodated.
In some embodiments, the battery modules may be assembled into a battery pack, and the number of the battery modules contained in the battery pack may be selected by one skilled in the art according to the application and capacity of the battery pack.
Fig. 4 and 5 are a battery pack 1 as an example. Referring to fig. 4 and 5, a battery pack 1 may include a battery case and a plurality of battery modules 4 disposed in the battery case. The battery box comprises an upper box body 2 and a lower box body 3, wherein the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4. A plurality of battery modules 4 may be arranged in any manner in the battery box.
Electric device
The present application also provides an electric device including the secondary battery, the battery module, or the battery pack provided by the present application. The secondary battery, the battery module, or the battery pack may be used as a power source of the electric device, and may also be used as an energy storage unit of the electric device. The powered device may include, but is not limited to, mobile devices (e.g., cell phones, laptops, etc.), electric vehicles (e.g., electric cars, hybrid electric cars, plug-in hybrid electric cars, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, and the like.
As the electricity-using device, a secondary battery, a battery module, or a battery pack may be selected according to its use requirement.
Fig. 6 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle or a plug-in hybrid electric vehicle and the like. In order to meet the demand of the electric device for high power and high energy density of the secondary battery, a battery pack or a battery module may be used.
As another example, the powered device may be a mobile phone, a tablet computer, a notebook computer, or the like. The electric device is generally required to be thin and light, and a secondary battery can be used as a power source.
Examples
Hereinafter, examples of the present application will be described. The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the present disclosure. The examples do not specify particular techniques or conditions, and are performed according to techniques or conditions described in literature in the art or according to the product specification. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
Example 1
Preparation of positive pole piece
LiNi to be used as a positive electrode active material 0.5 Co 0.2 Mn 0.3 O 2 Super P (timal corporation) as a conductive agent and polyvinylidene fluoride (PVDF) as a binder were uniformly mixed in N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The solid content in the positive electrode slurry was 50wt%, and LiNi was contained in the solid content 0.5 Co 0.2 Mn 0.3 O 2 The mass ratio of Super P to PVDF is 95. Coating the anode slurry on an anode current collector aluminum foil, drying at 85 ℃, cold-pressing, cutting edges, cutting pieces and dividing strips, and finally obtaining the anode current collector aluminum foilDrying for 4 hours at 85 ℃ under vacuum condition to prepare the positive pole piece.
Preparation of negative pole piece
Graphite as a negative electrode active material, super P (TiMCAL) as a conductive agent and styrene butadiene rubber as a binder were uniformly mixed in deionized water in a mass ratio of 95. The content of the binder in the unit area of the negative electrode film layer of the negative electrode slurry is 18mg/dm through the conventional process 2 The coating amount is uniformly coated on a copper foil of a negative current collector, the copper foil is dried at the temperature of 85 ℃, then cold pressing, trimming, cutting and slitting are carried out, and the copper foil is dried for 12 hours at the temperature of 120 ℃ under a vacuum condition to obtain a negative pole piece.
Preparation of the electrolyte
After uniformly mixing dimethyl carbonate and diethyl carbonate as linear carbonates, ethyl acetate as linear carboxylic acid esters, and Ethylene Carbonate (EC) as another solvent in a glove box under an argon atmosphere, 1M lithium hexafluorophosphate (LiPF) was slowly added dropwise thereto 6 ) As an electrolyte salt, the mixture was sufficiently stirred, and 100g of an electrolyte solution was obtained after the electrolyte salt was completely dissolved. Wherein the mass percent of dimethyl carbonate in the electrolyte is 15%, the mass percent of diethyl carbonate in the electrolyte is 15%, the mass percent of ethyl acetate in the electrolyte is 15%, and lithium hexafluorophosphate (LiPF) in the electrolyte 6 ) The mass percent of (2) is 12.5%, and the rest is Ethylene Carbonate (EC).
Preparation of the Battery
A16 μm polyethylene film was used as the separator. And stacking the positive pole piece and the diaphragm obtained in the above steps and the negative pole piece obtained in the above steps according to the sequence, so that the diaphragm is positioned between the positive pole piece and the negative pole piece to play a role in isolating the positive pole and the negative pole. And then wound to obtain a bare cell. A tab is welded on the bare cell, and the bare cell is housed in an aluminum case. And (3) baking the assembled battery at 100 ℃ to remove water, and then injecting the electrolyte obtained in the step to obtain the uncharged battery. The uncharged battery is subjected to standing, hot and cold pressing, formation, shaping and capacity testing in sequence to obtain the secondary battery (the thickness of the secondary battery is 4.0mm, the width of the secondary battery is 60mm, and the length of the secondary battery is 140 mm). For the obtained secondary battery, the conductivity, the adhesion of the negative electrode film layer, the charge rate performance, and the cycle capacity retention rate were measured. The structure of the secondary battery is shown in table 1, and the results of measuring the performance of the secondary battery are shown in table 2.
Measurement method
(1) Method for measuring content of binder per unit area of negative electrode film layer
Measuring a negative pole piece with the area of c by using a graduated scale, putting the negative pole piece into a beaker filled with deionized water, carrying out ultrasonic treatment, completely dropping a negative pole film layer from a negative pole current collector after about 1 hour, removing an active material and a conductive agent in the negative pole film layer by suction filtration because the active material and the conductive agent are insoluble in water, removing moisture by evaporation of a water-soluble binder, weighing the mass m of the binder, and calculating the mass of the binder on the unit area of the negative pole film layer by using the mass m/c, wherein the unit is as follows: mg/dm 2 。
(2) Method for measuring electrical conductivity
The conductivity of the electrolyte was measured with reference to HG-T4067-2015.
(3) Method for measuring adhesive force between negative electrode film layer and negative electrode current collector
Taking a fresh battery, discharging 1C to 2.8V, then disassembling the battery, drawing out a negative pole piece, and measuring the peel strength of a negative pole film layer on the negative pole piece according to the following steps after the electrolyte on the surface of the negative pole is completely volatilized. That is, a negative electrode plate with a length of 20cm and a width of 2cm is taken, one surface of the electrode plate is adhered to a steel plate by double-sided adhesive, the film layer is slightly torn, the film layer with the length of about 2cm is peeled from a current collector, one end of the steel plate is fixed on a clamp of a tensile machine and clamped on the clamp of the tensile machine, the peeled film layer is fixed on a clamp at the upper end of the tensile machine, the tensile machine is pulled at a speed of 30mm/min by adopting an Instron 3365 high-iron tensile machine, the film layer is slowly peeled from the current collector, the tensile value when the tensile force is stable is displayed on a computer, and the tensile value is the peeling strength value of the film layer.
(4) Method for measuring 2C charging rate performance
At 25 ℃, the cell was connected to a novyi charger, left to stand for 5min, discharged to 2.8V at 1C, left to stand for 5min, charged to 4.2V at 0.5C, the charge capacity C0 recorded, left to stand for 5min, discharged to 2.8V at 1C, left to stand for 5min, charged to 4.2V at 1C, left to stand for 5min, discharged to 2.8V at 1C, left to stand for 5min, charged to 4.2V at 2C, the charge capacity recorded as C1,2C charge rate = C1/C0.
(5) Retention ratio of circulating capacity
The cell was charged at 25 ℃ to 4.2V at 2C constant current, then charged at 4.2V constant voltage to a current of 0.05C, and then discharged at 1C constant current to 2.8V, which is a charge-discharge cycle. The capacity retention rate after 500 cycles of the battery was calculated with the first discharge capacity as 100%. Capacity retention (%) after 500 cycles of the battery was not = discharge capacity at 500 cycles/capacity at first discharge × 100%.
Examples 2 to 6 and comparative examples 1 to 4
Secondary batteries of examples 2 to 6 and comparative examples 1 to 4 were produced in the same manner as in example 1, except that the kinds and contents of linear carbonate and linear carboxylate in the electrolyte solution and the kinds and contents of the binder were changed as shown in table 1. For the obtained secondary battery, the conductivity, the adhesion of the negative electrode film layer, the charge rate performance, and the cycle capacity retention rate were measured. The results of measuring the performance of the secondary battery are shown in table 2.
TABLE 1
TABLE 2
| Conductivity (mS/cm) | Adhesion (N/m) | 2C charge rate performance | Retention rate of circulating capacity | |
| Example 1 | 10.2 | 10.4 | 98.3％ | 96.0％ |
| Example 2 | 9.0 | 10.7 | 98.6％ | 96.5％ |
| Example 3 | 9.7 | 10.5 | 99.0％ | 97.0％ |
| Example 4 | 10.5 | 10.2 | 97.0％ | 94.3％ |
| Example 5 | 14.0 | 10.6 | 99.5％ | 97.7％ |
| Example 6 | 13.0 | 10.4 | 99.3％ | 97.5％ |
| Comparative example 1 | 10.0 | 10.9 | 86.3％ | 82.4％ |
| Comparative example 2 | 15.3 | 11.1 | 84.2％ | 80.3％ |
| Comparative example 3 | 10.0 | 8.2 | 80.0％ | 75.4％ |
| Comparative example 4 | 8.8 | 6.2 | 78.2％ | 72.5％ |
As is clear from the data in tables 1 and 2, in examples 1 to 6, the relationship of 0.40A. Ltoreq. S.ltoreq.0.70A was satisfied between the total content of the linear carboxylic acid ester and the linear carbonate in the electrolyte and the content of the binder per unit area of the negative electrode film layer, the conductivity of the electrolyte and the adhesion between the negative electrode film layer and the negative electrode current collector were good, the 2C charge rate of the battery was 97% or more, and the cycle capacity retention rate was 94% or more. In contrast, in comparative examples 1 to 4, the relationship of 0.40A. Ltoreq.S.ltoreq.0.70A was not satisfied between the total content of the linear carboxylic acid ester and the linear carbonate in the electrolyte solution and the content of the binder per unit area of the negative electrode film layer, the 2C charge rate was less than 90%, and the cycle capacity retention rate was less than 90%. As can be seen from comparison between examples 1 to 6 and comparative examples 1 to 4, by adjusting the relationship between the total content of the linear carboxylate and the linear carbonate in the electrolyte and the content of the binder per unit area of the negative electrode film layer, the viscosity of the electrolyte can be ensured to be suitable for the ion kinetic conductivity, and the stability of the negative electrode sheet in the recycling process can be ensured, so that the quick charge performance and the cycle life of the secondary battery can be both considered.
The present application is not limited to the above embodiments. The above embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and exhibiting the same operation and effect within the technical scope of the present application are included in the technical scope of the present application. Various modifications that can be conceived by those skilled in the art are applied to the embodiments and other embodiments are also included in the scope of the present application, which are configured by combining some of the constituent elements in the embodiments without departing from the scope of the present application.
Claims (10)
1. A secondary battery is characterized in that,
comprises a negative pole piece and electrolyte,
the negative pole piece comprises a negative pole current collector and a negative pole film layer formed on the negative pole current collector, the negative pole film layer comprises a binder,
the electrolyte contains a linear carbonate and a linear carboxylate,
setting the sum of the mass percentage of the linear carbonate and the mass percentage of the linear carboxylate in the electrolyte asA%, and the content of the binder per unit area of the negative electrode film layer is S mg/dm 2 S and A satisfy the following relation:
0.40A≤S≤0.70A。
2. the secondary battery according to claim 1,
0.40A≤S≤0.60A。
3. the secondary battery according to claim 1 or 2,
the linear carbonate in the electrolyte is 10-50% by mass.
4. The secondary battery according to claim 1 or 2,
the mass percentage of the linear carboxylic ester in the electrolyte is 10-20%.
5. The secondary battery according to claim 1 or 2,
20％≤A％≤70％。
6. the secondary battery according to claim 1 or 2,
the content of the binder in the unit area of the negative electrode film layer is 8-60 mg/dm 2 。
7. The secondary battery according to claim 1 or 2,
the conductivity of the electrolyte is 9-15 mS/cm.
8. A battery module comprising the secondary battery according to any one of claims 1 to 7.
9. A battery pack comprising the battery module according to claim 8.
10. An electric device comprising at least one selected from the group consisting of the secondary battery according to any one of claims 1 to 7, the battery module according to claim 8, and the battery pack according to claim 9.
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