CN117894921A - Negative electrode sheet, secondary battery and device - Google Patents
Negative electrode sheet, secondary battery and device Download PDFInfo
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- CN117894921A CN117894921A CN202410155225.8A CN202410155225A CN117894921A CN 117894921 A CN117894921 A CN 117894921A CN 202410155225 A CN202410155225 A CN 202410155225A CN 117894921 A CN117894921 A CN 117894921A
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Classifications
-
- 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
Abstract
The application discloses negative pole piece, including the electric current collector with set up in the negative pole active material layer on electric current collector surface, negative pole active material layer includes graphite negative pole active material, wherein, the negative pole piece satisfies: r is more than or equal to 0.1 and less than or equal to 0.31, wherein R is the mass percentage of fluorine element in the graphite anode active material to the graphite anode active material; t is the resistivity of the negative electrode plate, and the unit is omega cm 2 The method comprises the steps of carrying out a first treatment on the surface of the M is the contact angle of the graphite anode active material, and the unit is degree. The graphite anode active material provided by the application has improved gram capacity, and the secondary battery comprising the graphite anode active material has improved first charge and discharge efficiency and long-cycle capacity.
Description
Technical Field
The invention relates to a negative electrode plate, in particular to a negative electrode plate, a secondary battery and a device comprising the secondary battery, and belongs to the field of batteries.
Background
The development of electric automobiles becomes one of the important ways of energy conservation and emission reduction. The power battery is a core component of the electric automobile, and a wet process and a dry process are still under development for the conventional negative electrode of the power battery which is produced in mass at present. Compared with the wet process, the dry process has the advantages of low energy consumption, short working procedure, easy control of process quality and the like, and the production cost is lower. Specifically, the wet process is to uniformly mix active substances, binders and conductive agents in a solvent to prepare a slurry mixture with the solid content of 40% -60%, then coating the slurry mixture on a solid sheet-shaped current collector, finally drying to evaporate the solvent, and removing the solvent in the electrode sheet film. The dry process has the advantages of low energy consumption and great cost, and the active material, the binder and the conductive agent are mixed, the mixture is fibrillated, the fibrillated material is formed into a dry electrode film, and then the dry electrode film is compounded with the solid current collector.
Therefore, there is an urgent need to develop a novel negative electrode tab.
Disclosure of Invention
Aiming at the defects of the prior art, the application provides a negative electrode plate, a secondary battery and a device comprising the secondary battery. The graphite negative electrode piece has lower resistivity and higher conductivity, is favorable for rapid migration of electrons, and the secondary battery comprising the negative electrode piece has improved primary charge and discharge efficiency, long circulation capacity and calendar life. More importantly, the graphite anode active material can meet the use requirement of a dry electrode, is more excellent in performance in the dry electrode and has obvious cost reduction effect.
The first aspect of the present application provides a negative electrode tab, including the current collector with set up in the negative electrode active material layer on current collector surface, negative electrode active material layer includes graphite negative electrode active material, wherein, the negative electrode tab satisfies: r is more than or equal to 0.1 and less than or equal to 0.31, wherein R is the mass percentage of fluorine element in the graphite anode active material to the graphite anode active material; t is the resistivity of the negative electrode plate, and the unit is omega cm 2 The method comprises the steps of carrying out a first treatment on the surface of the M is the contact angle of the graphite anode active material, and the unit is degree.
A second aspect of the present application provides a secondary battery comprising the negative electrode tab of the first aspect.
A third aspect of the present application provides an apparatus comprising the secondary battery according to the second aspect.
The dry pole piece provided by the application not only has excellent electronic conductivity, can meet the requirement of electronic rapid migration, but also has better liquid-retaining capacity, and can be fully contacted and infiltrated with electrolyte without loss.
Drawings
So that the manner in which the above recited objects, features and advantages of the present invention can be understood in detail, a more particular description of the invention, briefly summarized below, may be had by reference to the appended drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than as described herein, and therefore the present invention is not limited to the specific embodiments disclosed below.
Fig. 1 is an SEM image of natural graphite in example 1 of the present application.
Detailed Description
For simplicity, this application discloses only a few numerical ranges specifically. However, any lower limit may be combined with any upper limit to form a range not explicitly recited; and any lower limit may be combined with any other lower limit to form a range not explicitly recited, and any upper limit may be combined with any other upper limit to form a range not explicitly recited. Furthermore, each separately disclosed point or individual value may itself be combined as a lower limit or upper limit with any other point or individual value or with other lower limit or upper limit to form a range not explicitly recited.
Unless otherwise indicated, terms used in the present application have well-known meanings commonly understood by those skilled in the art. Unless otherwise indicated, the numerical values of the parameters set forth in this application may be measured by various measurement methods commonly used in the art (e.g., may be tested according to the methods set forth in the examples of this application).
The list of items to which the term "at least one of," "at least one of," or other similar terms are connected may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means only a; only B; or A and B. In another example, if items A, B and C are listed, then the phrase "at least one of A, B and C" means only a; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single component or multiple components. Item B may comprise a single component or multiple components. Item C may comprise a single component or multiple components.
The term "surface roughness" refers to the smoothness of the surface of the graphite anode active material.
The term "sphericity" refers to the ratio of the circular perimeter of the equivalent projected area of a particle to the actual perimeter of its projection. The term "S50" refers to the sphericity of a material at a cumulative frequency of 50% from the side where sphericity is low.
The term "Dv50" (also referred to as "median particle diameter") refers to a particle diameter of a material up to 50% by volume in a volume-based particle size distribution from the small particle diameter side, i.e., the volume of the material smaller than this particle diameter accounts for 50% of the total volume of the material.
The present application is further described below in conjunction with the detailed description. It should be understood that these specific embodiments are presented by way of example only and are not intended to limit the scope of the present application.
1. Negative pole piece
The application provides a negative pole piece include the electric current collector and set up in the negative pole active material layer on electric current collector surface, negative pole active material layer includes graphite negative pole active material, graphite negative pole active material contains fluorine element (F), wherein, the negative pole piece satisfies: the R multiplied by M+T is more than or equal to 0.1 and less than or equal to 0.31, the negative electrode plate meeting the application range can fully contact with the electrolyte, the electrolyte is ensured to reasonably infiltrate graphite, better electron conductivity is ensured, and the rapid migration of electrons in the negative electrode plate is met. Wherein R is the mass percentage of the fluorine element in the graphite anode active material; t is the resistivity of the negative electrode plate, and the unit is omega cm 2 The method comprises the steps of carrying out a first treatment on the surface of the M is the contact angle of the graphite anode active material, and the unit is degree.
In some embodiments, r×m+t is 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, or any range therebetween; in some embodiments, 0.11 R.ltoreq.RxM+T.ltoreq.0.29. If R is too small, the pole piece has strong imbibition capability, and can absorb a large amount of electrolyte, so that the free electrolyte is too little, the electrolyte is accelerated to dry, and the long-term use of the battery is not facilitated. If R×M+T is too large, it indicates that the negative electrode sheet is in poor contact with the electrolyte, and the wettability is poor, failing to exert the original performance of the battery.
In some embodiments, 0.05% R.ltoreq.0.55%; in some embodiments, R is 0.05%, 0.07%, 0.09%, 0.11%, 0.13%, 0.15%, 0.17%, 0.19%, 0.21%, 0.23%, 0.25%, 0.27%, 0.29%, 0.31%, 0.33%, 0.38%, 0.43%, 0.48%, 0.53%, 0.55%, or any range therebetween; in some embodiments, 0.12% R.ltoreq.0.48%; in some embodiments, 0.2% R.ltoreq.0.4%. The F element is taken as a special additive element and mainly takes part in the formation of SEI on the surface of the anode active material. If the content of F element is too large, a large amount of active lithium in the electrolyte is consumed, so that the first effect of the battery is reduced, the cycle life is shortened, the internal resistance of the battery is increased due to the fact that thicker SEI is generated, the heat generation amount during charging is increased, and potential safety hazards are brought; if the content of F element is too small, incomplete and uneven SEI film formation can be caused, and the film formation on the surface of the negative electrode active material has a missing part, so that side reaction cannot be prevented, the calendar life of the battery is reduced, and the storage performance is deteriorated.
In some embodiments, 20.ltoreq.M.ltoreq.60; in some embodiments, M is 20, 23, 26, 29, 32, 35, 38, 43, 48, 51, 54, 57, 60 or any range therebetween; in some embodiments, 23.ltoreq.M.ltoreq.58; in some embodiments, 29.ltoreq.M.ltoreq.50. The contact angle represents the contact characteristic of the surface of the pole piece and the surface of the electrolyte, the too small contact angle indicates that the electrolyte can be quickly absorbed by the active material, the liquid absorption capacity of the active material is too strong, free electrolyte and active lithium are insufficient, the electrolyte is dried too fast in the use process of the battery, and the cycle life is rather worse; too large contact angle indicates that the contact capability of the active material and the electrolyte is too poor, the electrolyte cannot fully infiltrate the active material, so that the active material cannot play the original function, and the free electrolyte and the excessive active lithium cause the aggravation of side reaction and the increase of gas production.
In some embodiments, 0.01.ltoreq.T.ltoreq.0.17; in some embodiments, T is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.09, 0.11, 0.13, 0.15, 0.17, or any range therebetween; in some embodiments, 0.03.ltoreq.T.ltoreq.0.15; in some embodiments, 0.052.ltoreq.T.ltoreq.0.097. The sheet resistivity (i.e., pole piece resistivity) represents the ability of the pole piece to conduct electricity, with smaller values indicating greater conductivity. If the resistivity of the pole piece is too small, the electron conducting capacity of the pole piece exceeds the original design requirement, so that the electron migration speed is too high, the reaction with lithium ions is faster, the occurrence of side reaction is aggravated, and the consumption of active lithium is accelerated; if the resistivity of the pole piece is too large, the electron conducting capacity is poor, the electron transfer speed cannot keep up with the ion transfer speed, lithium ions are separated out, and lithium separation occurs.
The graphite anode active material provided by the application meets the requirement of 1.1 percent to 3.5 percent, wherein,wherein A refers to the surface roughness of the graphite anode active material; s refers to the specific surface area of the graphite anode active material, and the unit is m 2 /g; b is Dv50 of the graphite anode active material, and the unit is mu m; t is the true density of the graphite anode active material, and the unit is kg/m 3 The method comprises the steps of carrying out a first treatment on the surface of the D means S50 of the graphite anode active material, wherein S50 means sphericity at which the cumulative frequency from the side where sphericity is low is 50%. The smaller the surface roughness A of the graphite anode active material is, the smoother the surface is, and the fewer the surface ravines are; the larger the surface roughness a, the more surface ravines and the less smooth the surface. The proper surface roughness can ensure that the surface of the anode active material has proper effective active sites, meets the requirement of lithium ion intercalation,thereby improving gram capacity of the active material, increasing contact area with electrolyte, making the graphite negative electrode active material have certain lipophilicity, proper surface tension and forming a complete SEI film, thereby fully protecting the inside of the negative electrode active material from being damaged by macromolecular solvents, and finally improving first charge and discharge efficiency, cycle life and calendar life of the battery. Accordingly, the graphite anode active material having the surface roughness of the present application range has an improved gram capacity, and the secondary battery including the graphite anode active material has an improved first charge and discharge efficiency and long cycle capacity.
In some embodiments, a is 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, 1.35%, 1.4%, 1.45%, 1.5%, 1.55%, 1.6%, 1.65%, 1.7%, 1.75%, 1.8%, 1.85%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5% or any range therebetween. If the surface roughness A is less than 1.2%, the surface is too smooth, the fewer surface ravines are, the surface tension and the adsorption force are extremely weak, lithium ion intercalation is not easy to absorb, the capacity is reduced, the formed SEI film is incomplete in wrapping, electrolyte is repeatedly consumed, the first cycle efficiency is reduced, and the cycle performance is reduced; if the surface roughness A is more than 3.5%, the more the surface ravines, the rough the surface, the increased sliding resistance between particles, so that the active material is difficult to disperse uniformly in the pole piece, the high surface density of the pole piece and the low surface density of the pole piece are caused, namely, the low gram capacity of the pole piece is caused, the uneven lithium intercalation of the pole piece is caused, and finally, the cycle life of the secondary battery is reduced. In some embodiments, 1.5% A.ltoreq.3.5%.
In some embodiments, 1.0m 2 /g≤S≤9.0m 2 /g; in some embodiments, S is 1.0m 2 /g、2.0m 2 /g、3.0m 2 /g、4.0m 2 /g、5.0m 2 /g、6.0m 2 /g、8.0m 2 /g、9.0m 2 G or any range therebetween; the specific surface area of the active material reflects the surface shape of the materialThe specific surface area is larger, the surface active sites of the material are more, the material is easy to react with electrolyte, and the whole battery performance is not improved, so that the specific surface area BET of the anode active material is required to be limited in the proper range; in some embodiments, 2.0m 2 /g≤S≤8.0m 2 /g。
In some embodiments, 2.0kg/m 3 ≤T≤2.5kg/m 3 The method comprises the steps of carrying out a first treatment on the surface of the In some embodiments, T is 2.0kg/m 3 、2.05kg/m 3 、2.1kg/m 3 、2.15kg/m 3 、2.2kg/m 3 、2.25kg/m 3 、2.3kg/m 3 、2.35kg/m 3 、2.4kg/m 3 、2.45kg/m 3 、2.5kg/m 3 Or any range therebetween; in some embodiments, 2.22kg/m 3 ≤T≤2.25kg/m 3 。
In some embodiments, 13.0 μm.ltoreq.B.ltoreq.20.0 μm; in some embodiments, B is 13.0 μm, 14.0 μm, 15.0 μm, 16.0 μm, 17.0 μm, 18.0 μm, 19.0 μm, 20 μm, or any range therebetween; in some embodiments, 15.0 μm.ltoreq.B.ltoreq.18.0 μm.
In some embodiments, 0.7.ltoreq.D.ltoreq.1.0; in some embodiments, D is 0.7, 0.72, 0.74, 0.76, 0.78, 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, 1.0, or any range therebetween; if S50 is too small, the pore of the negative electrode plate is longer and the pore diameter is smaller; if S50 is too large, the negative pole piece is difficult to realize higher compaction density; in some embodiments, 0.85.ltoreq.D.ltoreq.0.93.
In some embodiments, the graphite negative electrode active material includes at least one of natural graphite and artificial graphite.
In some embodiments, the natural graphite is spherical.
According to an embodiment of the present application, the preparation of the anode active material includes the steps of: 1) The precursor (for example, flake graphite, microcrystalline graphite, etc. can be selected according to the need) is crushed and spheroidized to obtain first spherical graphite with an average particle size of 4-25 μm; 2) Shaping and grading the prepared first spherical graphite to obtain second spherical graphite with the average particle diameter of 12-20 mu m; 3) Mixing the second spherical graphite and the coating agent, and carbonizing (coating carbonization may be omitted according to actual needs); 4) Sieving and demagnetizing. Of course, the preparation method of the anode active material is not limited thereto, but may also be prepared by other methods well known in the art.
In some embodiments, the negative electrode active material is prepared by the following method: the precursor (for example, flake graphite, microcrystalline graphite, etc. can be selected according to the need) is crushed and spheroidized to obtain spherical graphite with an average particle size of 4-25 μm; in the sphericizing process, the sphericity of the spherical graphite can be adjusted by adjusting parameters such as the frequency of a main machine of sphericizing equipment, the frequency of a grading impeller, the air quantity of a fan and the like; the prepared spherical graphite can enter a shaping machine through a feeding system to be polished, and the sphericity of a sample can be adjusted by adjusting the working frequency of a main machine of the shaping equipment, the working frequency of a grading impeller, the air quantity of a fan and other parameters. The method comprises the steps of (1) grading a sample through a self-flow grading area or a grader after adjusting the crushing degree of a precursor and the sphericizing and shaping to obtain spherical graphite with the average particle diameter of 12-20 mu m; mixing the spherical graphite subjected to shaping and grading treatment with a coating agent and carbonizing treatment (according to actual needs, coating carbonization treatment can be omitted); and finally, sieving and demagnetizing. Of course, the preparation method of the anode active material is not limited thereto, but may also be prepared by other methods well known in the art.
In some embodiments, the preparation of the graphite anode active material includes the steps of: crushing and sphericizing crystalline flake graphite or microcrystalline graphite to obtain first spherical graphite with an average particle size of 4-25 μm; the prepared first spherical graphite is subjected to acid washing purification to remove redundant impurities, and then is subjected to continuous shaping and classification to obtain second spherical graphite with the average particle size of 12-20 mu m; the second spheroidal graphite is mixed with a capping agent. Specifically, crushing and spheroidizing flake graphite or microcrystalline graphite to obtain first spherical graphite, wherein Dv50 of the first spherical graphite is 4-25 μm; acid washing and purifying the obtained first spherical graphite, wherein ash content after purification meets the range of 0.01% -0.04%, and continuously shaping and grading the purified first spherical graphite to obtain second spherical graphite, and the Dv50 of the second spherical graphite is 12-20 mu m; screening spherical graphite (used as a spherical graphite precursor) with Dv50 of 15.0-18.0 μm and sphericity of 0.7-1.0 from the obtained second spherical graphite, wherein screening equipment can be a combined integrated machine of a cyclone classifier and a shaper; coating the spherical graphite precursor obtained in the steps, wherein equipment used for coating can be one or more of a vertical coating kettle, a horizontal coating kettle, a roller furnace and a continuous rotary kiln, and a coating agent used for coating can be one or more of modified high-temperature asphalt with a softening point of 150-280 ℃ and a coking value of 45-95, or one or more of phenolic resin, starch, sucrose and the like; the proportion of the coating agent added can be 3% -8%; carrying out high-temperature carbonization treatment on the coated material, wherein the high-temperature carbonization equipment can be one or more of a roller kiln, a gas-fired tunnel kiln, a pusher kiln and a shuttle kiln, and the carbonization temperature is 1000-1400 ℃; and (3) carrying out finished product processing on the material subjected to high-temperature carbonization treatment to obtain the graphite anode active material, wherein the discharge capacity is 365mAh/g-367mAh/g, and the first cycle efficiency is 90.0% -95.0%.
The application provides a method for manufacturing a dry-method negative electrode plate, which comprises the following steps: a mixture is prepared by dry-mixing a negative electrode active material, a dried conductive material, and a dried binder, and a high shear force is applied to the mixture. The mixture is disposed on a current collector and the current collector on which the mixture is disposed is rolled.
In some embodiments, the method of preparing a dry negative electrode tab of the present application is a dry method without using a solvent and includes:
preparing a mixture by dry mixing a negative active material, a dried conductive material, and a dried binder, wherein the dried conductive material is carbon nanotubes or a combination of carbon nanotubes and carbon black, and the dried binder is polytetrafluoroethylene; applying a high shear force of 50N to 1000N to the mixture so that a mixture of particles in which the dried conductive material, the anode active material, and the dried binder are aggregated together is formed; the mixture is disposed on a current collector and the current collector on which the mixture is disposed is rolled.
In some embodiments, the method of preparing a dry negative electrode tab of the present application is a dry method without using a solvent and includes: (1) mixing: graphite anode active material, conductive agent SP, adhesive PTFE, carbon nano tube conductive paste CNT and additive PPS are mixed according to (97.0-97.5)%: 0.6%: (0.7-1.2)%: 0.2%: mixing 1% by mass, wherein equipment used for mixing is a dry internal mixer; (2) film formation: taking out the mixed powder, and rolling the powder into a sheet shape (membrane) by using a roller press for one-step forming and rolling, wherein the thickness of the membrane is 200-400 mu m; (3) thinning: thinning the membrane, and carrying out thinning rolling by using a thinning roller press (wherein the roller gap distance of the roller press is 100 mu m), and the thickness of the thinned membrane is 100 mu m-200 mu m; (4) compounding: compounding the thinned film with current collector of 7-8 microns thick carbon coated copper foil, pressing 10-20 microns film onto the carbon coated copper foil with a compounding roller press, and rolling to a compaction density of 1.55g/cm 2 ～1.65g/cm 2 Wherein, the thickness of one side is 75 μm-80 μm, the thickness of both sides is 150 μm-160 μm, the final complete negative plate is obtained, the stripping force of the plate is 30N/m-40N/m, the stripping speed is less than or equal to 20m/min, and the stripping angle is 180 degrees.
In some embodiments, the negative electrode tab includes a negative electrode material layer including a negative electrode active material including a carbon-based material, or a mixture of a carbon-based material and at least one material selected from a silicon-based material, a tin-based material, a phosphorus-based material, and metallic lithium.
In some embodiments, the silicon-based material includes at least one of silicon, a silicon alloy, a silicon oxygen compound, and a silicon carbon compound. In some embodiments, the carbon-based material comprises at least one of graphite, soft carbon, hard carbon, carbon nanotubes, and graphene. In some embodiments, the tin-based material includes at least one of tin, tin oxide, and tin alloy. In some embodiments, the phosphorus-based material includes phosphorus and/or a phosphorus complex.
In some embodiments, the negative electrode material layer further includes a binder. In some embodiments, the binder includes, but is not limited to: polytetrafluoroethylene (PTFE), polyolefins, polyethers, styrene-butadiene, polysiloxanes and copolymers of polysiloxanes, branched polyethers, polyvinyl ethers, copolymers thereof and/or mixtures thereof.
In some embodiments, the negative electrode further comprises a negative electrode current collector comprising: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof. The secondary battery of the present application also includes an electrolyte, which in some embodiments includes a lithium salt and a solvent.
In some embodiments, the secondary battery is a lithium secondary battery or a sodium secondary battery. In some embodiments, lithium secondary batteries include, but are not limited to: lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries.
In some embodiments, the secondary battery may include an outer package, which may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The exterior package of the secondary battery may also be a pouch type pouch, for example. The soft bag can be made of one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.
In some embodiments, the shape of the secondary battery is not particularly limited, and may be cylindrical, square, or any other shape.
In some embodiments, the present application also provides a battery module. The battery module includes the secondary battery described above. The battery module of the present application employs the above-described secondary battery, and thus has at least the same advantages as the secondary battery. The number of secondary batteries contained in the battery module of the present application may be plural, and the specific number may be adjusted according to the application and capacity of the battery module.
In some embodiments, the present application also provides a battery pack including the above battery module. The number of battery modules included in the battery pack may be adjusted according to the application and capacity of the battery pack.
The present application also provides an apparatus comprising at least one of the above secondary battery, battery module or battery pack.
In some embodiments, the apparatus includes, but is not limited to: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric storage systems, and the like. In order to meet the high power and high energy density requirements of the device for the secondary battery, a battery pack or a battery module may be employed.
In other embodiments, the device may be a cell phone, tablet, notebook, or the like. The device is generally required to be light and thin, and a secondary battery can be used as a power source.
In order to make the objects, technical solutions and advantageous technical effects of the present application clearer, the present application is further described in detail with reference to examples below. However, it should be understood that the examples of the present application are merely for the purpose of explaining the present application and are not intended to limit the present application, and the examples of the present application are not limited to the examples given in the specification. The specific experimental or operating conditions were not noted in the examples and were made under conventional conditions or under conditions recommended by the material suppliers.
The graphites in the following examples and comparative examples are both commercially available.
Examples and comparative examples
Example 1
1) Preparation of button half-cell:
preparing a negative electrode plate: natural graphite, a conductive agent SP, a binder PTFE, a conductive paste CNT and an additive PPS in a mass ratio of 97.2%:0.6%:1%:0.2%:1% of the carbon-coated copper foil is mixed, dispersed and fibrillated into a film, and then the film is thermally compounded with the carbon-coated copper foil to prepare the negative electrode plate.
Preparation of CR2016 type button half-cell: taking a metal lithium sheet as a counter electrode; in 1M LiPF 6 EC: DEC: DMC (1:1:1) is electrolyte; a polypropylene microporous membrane model 2400 Celgard is used as a diaphragm. All cells were assembled in a glove box filled with Ar gas.
2) Preparation of soft-pack full cell:
preparing a positive electrode plate: lithium iron phosphate, conductive agent (Super P), binder (PVDF) at 97:1.4: mixing in a ratio of 1.6, adding a solvent (NMP), and stirring under the action of a vacuum stirrer until the system becomes uniform and transparent, thereby obtaining the anode slurry. Uniformly coating the anode slurry on an anode current collector aluminum foil; and (3) airing the anode current collector coated with the anode slurry at room temperature, transferring to an oven for drying, and then carrying out cold pressing and slitting to obtain the anode sheet.
Preparing a negative electrode plate: as above.
Preparation of electrolyte: ethylene Carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) are mixed according to the volume ratio of 1:1:1, and then fully dried lithium salt LiPF6 is dissolved in a mixed organic solvent according to the proportion of 1mol/L to prepare an electrolyte.
Preparation of the separator: polyethylene film is used.
Assembling a battery: and sequentially stacking the positive pole piece, the diaphragm and the negative pole piece, so that the diaphragm is positioned between the positive pole piece and the negative pole piece to play a role in isolation, and then stacking to obtain the bare cell. And placing the bare cell in an outer packaging shell, injecting the prepared electrolyte into the dried bare cell, and performing vacuum packaging, standing, formation, shaping and other procedures to obtain the soft-package full-battery.
Examples 2 to 8 and comparative examples 1 to 6
Examples 2 to 8 and comparative examples 1 to 6 are achieved by adjusting characteristic parameters (e.g., fluorine content, contact angle, etc.) of the anode active material (natural graphite) and parameters (e.g., resistivity) of the electrode sheet on the basis of example 1, wherein the resistivity can be achieved by adjusting parameters of the content of the conductive agent, whether the current collector has a carbon coating, conductivity of the anode active material, thickness of the electrode sheet, compacted density, etc.
The specific adjustment measures and detailed data are shown in Table 1.
Measurement method
1. Testing parameters of graphite cathode active materials
(1) Particle size distribution testing
The particle size distribution was measured according to the particle size distribution laser diffraction method GB/T19077-2016 using a laser diffraction particle size distribution measuring instrument (Mastersizer 3000). For the volume distribution, the particle diameter at which the cumulative frequency from the small particle diameter side is 50% is Dv50.
(2) Sphericity distribution test
Using a dynamic particle image analyzer (QICPIC type manufactured by Sympatec corporation), the sphericity at which the cumulative frequency from the side where the sphericity measured by the dynamic particle image analyzer is low is 50% was S50.
(3) Testing of specific surface area
See GB/T19587-2017 for a method specified in the determination of specific surface area of solid substances by the gas adsorption BET method.
(4) Testing of true Density
See GB/T6155-1985-conventional determination of true density in the determination of true density of carbon materials.
(5) Testing the mass percentage of fluorine element in the graphite anode active material
May be measured by Inductively Coupled Plasma (ICP) analysis methods.
(6) Contact angle test
Adding graphite powder into a pre-mold, and pressing to form, wherein the formed graphite powder is only required to be capable of holding liquid drops; water contact angle measurements were carried out at 25 c±5 ℃ using a contact angle tester (e.g., SDC-200S): the water drop is dripped on the surface of the formed artificial graphite powder, the quantity of the water drop is 10 mu L+/-1 mu L, the water contact angle is tested 3-5 seconds after the water drop is dripped, specifically, the average value of the angles of the left side and the right side of the water drop is adopted for measuring the water contact angle, and the specific value is automatically fit and read by an instrument.
2. Pole piece performance test
(1) Testing of resistivity of negative electrode sheet
The four-probe method is adopted to test the resistance of the diaphragm, and the specific steps are as follows: a. placing the pole piece on a testing device to enable the surface of the pole piece to be flat; b. adjusting the pressure gauge to 0.001MPa to fix the test sample, and ensuring that the probe is well contacted with the sample; c. starting a testing device, introducing current into a sample to be tested through circuit connection, and recording voltage change; d. and calculating the resistance value of the sample according to ohm's law.
3. Battery performance test
(1) Testing of the Capacity of the Ke and the first charge and discharge efficiency (first Effect)
The materials of examples 1 to 8 and the natural graphite active materials of comparative examples 1 to 6 were prepared into button cells, and the prepared button cells were tested on an arbin bt2000 type battery tester in the united states under the following conditions: according to the constant-current charge and discharge of 1C, the charge and discharge voltage range is as follows: 0.1V-2V. Firstly, placing the battery tester for 16 hours to perform constant temperature, and then discharging the battery tester to 5mV at a constant current of 0.1 ℃; standing for 5min, and discharging to 5mV at constant current of 0.05C; standing for 5min, and discharging to 5mV at constant current of 0.02 ℃; standing for 5min, and finally discharging to 5mV at constant current of 0.01C, standing for 10min, thereby completing the first-turn discharge test. Then charging to 2V at constant current of 0.1C, standing for 10min, and completing the first-round charging test. The capacity recorded in the first-cycle charging process is taken as the charging capacity, and the ratio of the first-cycle charging capacity to the discharge capacity is taken as the first-time charging and discharging efficiency.
(2) Testing of full cell first charge and discharge efficiency (first effect) and cycle performance (500 turns)
The materials of examples 1 to 8 and the materials of comparative examples 1 to 6 were made into soft-pack cells, and the cycle performance test at room temperature of 25℃was conducted on a New Wei battery test cabinet,
the first-effect test method comprises the following steps: the method for specifically testing the soft package battery core forming section data and the capacity-dividing section data are taken as the capacity of the soft package battery core first-circle charging, and the method comprises the following steps: standing for 5min, performing constant temperature treatment, charging for 120min at 0.05C constant current, charging for 60min at 0.1C constant current after standing for 5min, charging for 54 min at 0.33C constant current after standing for 5min, and ending the formation section charging after standing for 5min, wherein the charging depth is 70% of SOC; then enters a capacity-dividing section, and is charged to 3.8V at a constant current of 0.33C, and the charging depth is 100% SOC. And taking the sum of the filling capacity of the formation section and the filling capacity of the capacity-dividing section to record as the first circle of filling capacity. Then, 0.33C was discharged to 2.3V, and then 0.1C was discharged to 2.2V, and the discharge capacity was recorded as the first-turn discharge capacity, first-effect=first-turn discharge capacity/first-turn charge capacity.
The capacity retention test method after 500cls is: and (3) performing constant-current discharge on the lithium ion battery according to the current of 1C at the normal temperature of 25 ℃, and then performing constant-current charge according to the current of 1C, wherein the cutoff voltage is 2.3V, and the cutoff voltage is 3.8V, so that the operation is repeated.
After 500 cycles of charge and discharge, the capacity retention after 500 th cycle was calculated according to the following formula:
the values of capacity during the cycle were tested according to conventional test methods in the art.
(3) Calendar life capacity retention test
And (3) at the normal temperature of 25 ℃, carrying out constant current charging on a fresh soft-packaged battery cell (lithium ion battery) according to the current of 0.5C, wherein the cutoff voltage is 3.8V, then carrying out constant current discharging according to the current of 0.5C, wherein the cutoff voltage is 2.3V, and recording the capacity of the first discharging as a calculation reference value. And then charging according to the constant current of 0.5C, and fully charging with the cut-off voltage of 3.8V, and placing the fully charged battery in a 45 ℃ incubator for preservation, wherein the battery is kept for 60 days without opening the incubator. And taking out the battery after 60 days, placing the battery at the normal temperature of 25 ℃ for 6-8 hours, performing discharge test after the battery is restored to 25 ℃, performing constant-current discharge according to 0.5C current, and recording that the discharge capacity is that after the battery is stored for 60 days at 45 ℃ when the cut-off voltage is 2.3V. The calendar life capacity retention at 45℃for 60 days was calculated as follows:
the test results are shown in tables 1-2.
TABLE 1
TABLE 2
As can be seen from tables 1 to 2, examples 1 to 8 have improved gram capacity and first cycle efficiency, both of the button cell and the full cell (lithium ion secondary battery), and the first cycle efficiency was improved, and the gram capacity thereof satisfied the range of 365mAh/g-367mAh/g, and was excellent in cycle performance, 500cls. After-cycle capacity retention was 89% or more, and 60 days 45℃calendar life capacity retention was 93.5% or more. The performance of comparative examples 1 to 6 was significantly reduced compared to examples 1 to 8, and specifically, the first cycle efficiency was much lower than that of examples 1 to 8, and the second gram capacity was also low, and did not satisfy the 365mAh/g-367mAh/g range, and most importantly, the 500cls post-cycle capacity retention was less than 89%, the 60 day 45℃calendar life capacity retention was less than 92.5%, and the cycle use requirements were not satisfied.
While certain exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. Rather, one of ordinary skill in the art will recognize that certain modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application, as described in the appended claims.
Claims (10)
1. The negative electrode plate comprises a current collector and a negative electrode active material layer arranged on the surface of the current collector, wherein the negative electrode active material layer comprises graphite negative electrode active materials, and the graphite negative electrode active materials contain fluorine, and the negative electrode plate meets the following conditions: r x M+T is more than or equal to 0.1 and less than or equal to 0.31,
r is the mass percentage of the fluorine element in the graphite anode active material;
t is the resistivity of the negative electrode plate, and the unit is omega cm 2 ；
M is the contact angle of the graphite anode active material, and the unit is degree.
2. The negative electrode tab of claim 1, wherein 0.11 +.r x m+t +.0.29.
3. The negative electrode tab according to claim 1 or 2, characterized in that it satisfies at least one of the following conditions:
0.05％≤R≤0.55％；
20≤M≤60；
0.01≤T≤0.17。
4. the negative electrode tab of claim 3, wherein the negative electrode tab satisfies at least one of the following conditions:
0.12％≤R≤0.48％；
23≤M≤58；
0.03≤T≤0.15。
5. the negative electrode tab according to claim 1 or 2, wherein the graphite negative electrode active material satisfies 1.1% or more and 3.5% or less of A, wherein,wherein,
a refers to the surface roughness of the graphite anode active material;
s refers to the specific surface area of the graphite anode active material, and the unit is m 2 /g；
B is Dv50 of the graphite anode active material, and the unit is mu m;
t is the true density of the graphite anode active material, and the unit is kg/m 3 ；
D means S50 of the graphite anode active material, wherein S50 means sphericity at which the cumulative frequency from the side where sphericity is low is 50%.
6. The negative electrode tab of claim 5, wherein the negative electrode tab satisfies at least one of the following conditions:
1.5％≤A≤3.5％；
1.0m 2 /g≤S≤9.0m 2 /g；
2.0kg/m 3 ≤T≤2.5kg/m 3 ；
13.0μm≤B≤20.0μm；
0.7≤D≤1.0。
7. the negative electrode tab of claim 6, wherein the negative electrode tab satisfies at least one of the following conditions:
2.0m 2 /g≤S≤8.0m 2 /g；
2.22kg/m 3 ≤T≤2.25kg/m 3 ；
15.0μm≤B≤18.0μm；
0.85≤D≤0.93。
8. the negative electrode tab of claim 1 or 2, wherein the graphite negative electrode active material comprises at least one of natural graphite and artificial graphite.
9. A secondary battery comprising the negative electrode tab according to any one of claims 1 to 8.
10. An apparatus comprising the secondary battery according to any one of claims 1 to 9.
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