CN118589019A - Battery cell - Google Patents

Battery cell Download PDF

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Publication number
CN118589019A
CN118589019A CN202410862611.0A CN202410862611A CN118589019A CN 118589019 A CN118589019 A CN 118589019A CN 202410862611 A CN202410862611 A CN 202410862611A CN 118589019 A CN118589019 A CN 118589019A
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battery
less
electrolyte
formula
equal
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于智力
邱亚明
王海
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Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery Co Ltd
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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 invention provides a battery, which comprises a positive plate, a negative plate, a diaphragm and electrolyte, wherein the positive plate comprises a positive current collector and a positive active layer arranged on at least one side surface of the positive current collector, the positive active layer comprises a lithium cobaltate material, and the mass percentage of cobalt element in the positive active layer is W Co; the electrolyte comprises fluoroacetonitrile and polynitrile compounds; based on the mass of the electrolyte, the mass percentage of the fluoroacetonitrile is W a, and the mass percentage of the polynitrile compound is W b; wherein, W a+Wb)/WCo is less than or equal to 0.12 and less than or equal to 1.12, the invention uses the fluoro-acetonitrile and the polynitrile compound in the electrolyte in a matching way, and controls the content of the fluoro-acetonitrile and the polynitrile compound and the cobalt element content in the positive electrode active layer to meet the above relation, thereby leading the battery to have excellent cycle performance, quick charge performance and storage performance under high voltage.

Description

Battery cell
Technical Field
The invention belongs to the technical field of batteries, and relates to a battery.
Background
With the development of electric vehicles, energy storage systems and other high-energy consumption applications, the requirements on the energy density and the charging speed of lithium ion batteries are increasingly high.
The energy density of a lithium ion battery is closely related to the energy density of the anode material and the cathode material and the working voltage of the battery. Therefore, the improvement of the compaction density and gram capacity of the anode and cathode materials of the battery and the improvement of the working voltage of the lithium ion battery are effective ways for increasing the energy density of the battery. Compared with other positive electrode materials, the lithium cobaltate material has the advantages of high specific capacity, high voltage and high-rate discharge, and is beneficial to increasing the energy density of the battery. However, the lithium cobaltate material has poor structural stability, and as the voltage increases, the lithium cobaltate material can undergo phase change, so that the volume of material particles expands and contracts, the volume deformation not only affects the structural stability of the material, but also can cause the damage of the electrode material and the attenuation of the cell performance, and the cycle performance of the battery under high voltage is deteriorated.
The charging speed of the lithium ion battery is closely related to the conductivity of the electrolyte. The electrolyte which is conventionally used in the field and is suitable for a high-voltage quick-charging system generally comprises a polynitrile compound, the compound has a relatively wide electrochemical window and ionic conductivity, and can form a good protection film on the positive electrode to avoid side reactions of a positive electrode material and the electrolyte, but the compound has poor compatibility with a negative electrode material, so that the interface impedance of an interface impedance battery is large, the internal resistance is high, and the cycle performance and the storage performance of the battery are not facilitated.
Therefore, how to make a battery have good cycle performance and storage performance at high voltage is a technical problem to be solved in the art.
Disclosure of Invention
The invention provides a battery, which is characterized in that fluoroacetonitrile and polynitrile compounds are matched in electrolyte for use, and the content of the fluoroacetonitrile and the polynitrile compounds and the cobalt content in an anode active layer are controlled to meet the relational expression, so that the battery has excellent cycle performance, quick charge performance and storage performance at high voltage.
The invention provides a battery, which comprises a positive plate, a negative plate, a diaphragm and electrolyte, wherein the positive plate comprises a positive current collector and a positive active layer arranged on at least one side surface of the positive current collector, and the positive active layer comprises a lithium cobaltate material; the mass percentage of cobalt element in the positive electrode active layer is W Co;
The electrolyte comprises fluoroacetonitrile and polynitrile compounds; based on the mass of the electrolyte, the mass percentage of the fluoroacetonitrile is W a, and the mass percentage of the polynitrile compound is W b;
Wherein, W a+Wb)/WCo is more than or equal to 0.12 and less than or equal to 1.12.
In the present invention, the polynitrile compound means a nitrile compound having at least two cyano groups.
Cyano is a high-activity functional group which can coordinate with cobalt element in the positive electrode active layer, so that a good protective film is formed at the interface between the positive electrode and the electrolyte, and side reactions of a lithium cobaltate material and the electrolyte are avoided. However, the negative electrode is usually made of carbon material or silicon material, which has high inertia and is not easy to have high interaction force with cyano functional groups, so that the traditional polynitrile compound in the electrolyte has poor compatibility with the negative electrode, so that the interface impedance between the negative electrode and the electrolyte is high, the internal resistance of the battery is increased, and the cycle performance and the storage performance of the battery are not good.
Based on the method, the fluoroacetonitrile is added into the electrolyte, compared with the traditional nitrile compound in the electrolyte, the F atom contained in the fluoroacetonitrile has extremely strong electronegativity, and can react with a carbon material or a silicon material with relatively strong inertia in the cathode to form stable C-F or Si-F bonds, so that the compatibility of the electrolyte and the cathode is enhanced, the internal resistance of a battery is reduced, and the improvement of the cycle performance and the storage performance of the battery is facilitated.
In addition, the fluoro-acetonitrile and the polynitrile compound are compounded, the fluoro-acetonitrile has smaller viscosity and is easy to transmit in the electrolyte, the film can be formed on the surface of the positive electrode better than the polynitrile compound, the formed film contains C-F bonds, the transmission of lithium ions is facilitated, the polynitrile compound is coordinated with cobalt ions in the positive electrode material to form a film on the basis of the fluoro-acetonitrile film formation, a metal dissolution channel is blocked, the structural stability of the lithium cobaltate material is enhanced, and therefore, the inner protective film formed by the fluoro-acetonitrile and the outer protective film formed by the polynitrile compound are synergistic, the dissolution of cobalt elements is effectively avoided while the transmission of the lithium ions is not influenced, and the side reaction of the positive electrode material and the electrolyte is reduced.
In summary, the inventor researches the synergistic effect of the fluoroacetonitrile content W a, the polynitrile compound content W b and the cobalt element content W c, and discovers that when the three contents are less than or equal to 0.12 (W a+Wb)/WCo is less than or equal to 1.12), the electrolyte and the negative electrode have lower interface impedance, the structural stability of the positive electrode material can be enhanced, the dissolution of the cobalt element is avoided, and the battery has excellent cycle performance and storage performance.
The polynitriles of the invention include, but are not limited to, succinonitrile (SN), glutaronitrile, adiponitrile (AND), 1, 5-dicyanopentane, 1, 6-dicyanohexane, 1, 7-dicyanoheptane, 1, 8-dicyanooctane, 1, 9-dicyanononane, 1, 10-dicyanodecane, 1, 12-dicyanododecane, tetramethylsuccinonitrile, 2-methylglutaronitrile, 2, 4-dimethylglutaronitrile, 2, 4-tetramethylglutaronitrile, 1, 4-dicyanopentane, 2, 6-dicyanoheptane, 2, 7-dicyanooctane, 2, 8-dicyanononane, 1, 6-dicyanodecane, 1, 2-dicyanobenzene, 1, 3-dicyanobenzene, 1, 4-dicyanobenzene 3, 5-dioxa-pimelic acid dinitrile, 1, 4-bis (cyanoethoxy) butane, ethylene glycol bis (2-cyanoethyl) ether, diethylene glycol bis (2-cyanoethyl) ether, triethylene glycol bis (2-cyanoethyl) ether, tetraethylene glycol bis (2-cyanoethyl) ether, 3,6,9,12,15,18-hexaoxaeicosanoic acid dinitrile, 1, 3-bis (2-cyanoethoxy) propane, 1, 4-bis (2-cyanoethoxy) butane, 1, 5-bis (2-cyanoethoxy) pentane, ethylene glycol bis (4-cyanobutyl) ether, 1, 4-dicyano-2-butene, 1, 4-dicyano-2-methyl-2-butene, 1, 4-dicyano-2-ethyl-2-butene, 1, 4-dicyano-2, 3-dimethyl-2-butene, 1, 4-dicyano-2, 3-diethyl-2-butene, 1, 6-dicyano-3-hexene, 1, 6-dicyano-2-methyl-3-hexene and 1, 6-dicyano-2-methyl-5-methyl-3-hexene, 1,3, 5-valeronitrile, 1,2, 3-propiotriazonitrile, 1,3, 6-Hexanetrinitrile (HTCN), 1,2, 6-hexanetrinitrile, 1,2, 3-tris (2-cyanoethoxy) propane, 1,2, 4-tris (2-cyanoethoxy) butane, 1-tris (cyanoethoxymethylene) ethane, 1-tris (cyanoethoxymethylene) propane, 3-methyl-1, 3, 5-tris (cyanoethoxy) pentane, 1,2, 7-tris (cyanoethoxy) heptane, 1,2, 6-tris (cyanoethoxy) hexane, tris (cyanoethoxy) phosphate and 1,2, 5-tris (cyanoethoxy) pentane.
In a preferred embodiment, (W a 2-Wb 2)/Wa is less than or equal to 0.80. The fluoroacetonitrile and the polynitrile compound meet the relational expression, the fluoroacetonitrile can form a layer of stable surface film on the surface of the positive electrode in preference to the polynitrile compound, the structural stability of the positive electrode material is enhanced, meanwhile, the transmission path of lithium ions on the surface of the positive electrode material is optimized, the transmission resistance is reduced, on the basis, the polynitrile compound coordinates with cobalt ions in the positive electrode material again to block a metal dissolution channel, and meanwhile, the mass transfer interface film formed on the basis of an inner layer does not influence the transmission performance of lithium ions while effectively protecting the positive electrode interface, and the rapid transmission of lithium ions under the condition of rapid charging is ensured.
When the content of the fluoroacetonitrile in the electrolyte is low, the viscosity of the electrolyte is high, and the compatibility with the negative electrode is poor; when the content of the fluoroacetonitrile is higher, the cyano content in the electrolyte is lower, which is unfavorable for coordination with the positive electrode material and has limited protection effect on the positive electrode. In order to have both a low viscosity of the electrolyte and to maintain proper fluorine and cyano concentrations in the electrolyte, 5% or less W a% or less 85%, preferably 10% or less W a% or less 60% is controlled. Illustratively, W a may be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or a range of any two values therein.
Also for the purpose of imparting both a lower viscosity and a suitable cyano concentration to the electrolyte, 2% or less W b% or less 10%, preferably 4% or less W b% or less 6% is controlled. Illustratively, W b may be 2%, 4%, 4.5%, 5%, 5.5%, 6%, 8%, 10% or a range of any two values therein.
The higher the cobalt element content in the positive electrode active layer is, the more favorable the improvement of the energy density of the battery is; however, the higher the cobalt element content, the poorer the structural stability of the positive electrode sheet. In order to have both good positive electrode stability and energy density of the battery, 35% or less W Co% or less 65%, preferably 54.8% or less W Co% or less 63.1% is controlled.
In a preferred embodiment, the electrolyte further comprises an additive of formula I:
A-B-C formula I;
In the formula I, A is selected from a structure shown in a formula Ia or a formula Ib, B is selected from a single bond, H or a structure shown in a formula Ic, and C is selected from H, a structure shown in a formula Id or a structure shown in Ie;
in the formula Ia, X 1 is selected from-O-or-CH 2-,n1 and is an integer between 0 and 4;
In the formula Ib, X 2 is selected from-O-or-CH 2-,n2 and is an integer between 0 and 3;
In the formula (Ic), X 3 and X 4 are each independently selected from-O-or-CH 2-,Y1 is selected from-C (O) -or-S (O) 2 -;
In the formula Id, X 5 and X 6 are each independently selected from-O-or-CH 2-,Y2 is selected from-C (O) -or-S (O) 2-,n3 and are integers between 0 and 4;
In formula Ie, X 7 is selected from-O-or-CH 2-,n4 and is an integer between 0 and 3.
In the above-mentioned structural formula, the catalyst,Indicating bonding to other groups at that position.
The lithium ion has higher solvation degree in the fluoroacetonitrile solvent, so that the desolvation resistance is higher when the lithium ion is intercalated into the anode and the cathode, the sulfur atom in the additive shown in the formula I can provide lone pair electrons, and forms stronger coordination bond with the lithium ion, so that the coordination environment between the lithium ion and the fluoroacetonitrile is improved, the coordination adjustment can weaken the solvation capacity of the lithium ion in the fluoroacetonitrile, reduce the interaction force between the lithium ion and the fluoroacetonitrile, improve the deintercalation speed of the lithium ion in the fluoroacetonitrile solvent, better improve the kinetic performance of the ion in electrolyte, and further improve the quick charge performance of a battery.
In addition, the SEI film with Li 2SO3 as the main component can be formed on the surface of the negative electrode by the additive shown in the formula I, the film has higher density and strength, liF can be formed on the surface of the negative electrode by the fluoroacetonitrile, and the LiF is cooperated with the SEI film with Li 2SO3 as the main component, so that the SEI film has better mechanical strength, is not easy to damage in the circulating process, and forms better protection on the interface of the negative electrode.
In addition, the sulfonic group in the additive shown in the formula I can form a CEI film on the surface of the positive electrode, so that the interface of the positive electrode is protected, the side reaction between the electrolyte and the positive electrode material is avoided, the cyclic expansion of the battery is further inhibited, and the cycle life of the battery is prolonged.
In a preferred embodiment, the additive of formula I is selected from one of the following compounds:
Taking the compound shown as the formula I-2 as an example, the additive shown as the formula I can be prepared by referring to the following method:
2,4:3, 5-di-O-benzylidene-L-iditol and 2, 2-dimethoxypropane are simultaneously placed in a reaction vessel, a catalyst p-TsOH is added into the reaction vessel, an intermediate compound 1 is obtained after the reaction, the obtained intermediate compound 1 is mixed with dimethyl carbonate and TBD and reacts to obtain an intermediate compound 2, p-TsOH is added into the reaction vessel to obtain a compound 3, thionyl chloride is added into the reaction vessel on the basis of the intermediate compound to obtain a compound 4, ruCl 3 is taken as a catalyst, naIO 4 is taken as an oxidant, and the compound 4 is oxidized to obtain the compound shown in the formula I-2.
In a preferred embodiment, the electrolyte further comprises lithium salt, the mass percentage of the lithium salt is W d based on the mass of the electrolyte, the mass percentage of the additive shown in the formula I is W c, and W d/Wc is more than or equal to 3.
As described above, when the contents of the lithium salt and the additive represented by formula I in the electrolyte satisfy the above relationship, the improvement of the stability of the negative electrode interface is further facilitated, and the cycle performance of the battery is improved.
The lithium salts of the present invention include, but are not limited to, one or more of lithium hexafluorophosphate (LiPF 6), lithium difluorophosphate (LiPO 2F2), lithium difluorooxalato borate (lipfob), lithium bis (trifluoromethylsulfonyl) imide, lithium difluorobis (oxalato) phosphate, lithium tetrafluoroborate, lithium bis (oxalato) borate, lithium hexafluoroantimonate, lithium hexafluoroarsonate, lithium bis (trifluoromethylsulfonyl) imide, lithium bis (pentafluoroethylsulfonyl) imide, lithium tris (trifluoromethylsulfonyl) methyl or lithium bis (trifluoromethylsulfonyl) imide.
In a preferred embodiment, 0.5% or less W c% or less 10% or less. Illustratively, the additive of formula I comprises 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% by mass or any two values thereof.
In a preferred embodiment, 5% or less W d% or less than 30%, preferably 10% or less W d% or less than 20%, more preferably 12% or less W d% or less than 17%.
In a preferred embodiment, the lithium cobaltate material comprises first particles and second particles, the ratio of the particle sizes of the first particles and the second particles being N, wherein 3.ltoreq.N.ltoreq.6.5.
The lithium cobaltate material with larger particles is favorable for providing better electron conduction performance and higher charge-discharge multiplying power, is favorable for outputting the whole power of the battery, and the smaller particle size can provide larger specific surface area, is favorable for increasing the contact area between the electrode and the electrolyte, and improves the ion transmission efficiency and the material capacity. Therefore, the electron and conduction properties and the ion transport efficiency can be balanced by adopting the first particles having a larger particle size and the second particles having a smaller particle size in the above particle size range ratio.
Further, the D50 particle diameter of the first particles is 15-35 mu m; and/or the second particles have a D50 particle size of 5 to 20 μm. Illustratively, the first particles have a D50 particle size of 15 μm, 20 μm, 25 μm, 30 μm, 35 μm or a range of values consisting of any two of these values, and the second particles have a D50 particle size of 5 μm, 10 μm, 15 μm, 20 μm or a range of values consisting of any two of these values.
In a preferred embodiment, W a/N is ≡0.012. When the ratio of the content of the fluoroacetonitrile in the electrolyte and the D50 particle size of the first particles and the second particles in the lithium cobaltate material meets the above ratio, the lithium cobaltate material interface and the electrolyte interface have good contact, so that the ion transmission distance is shortened, the internal resistance of the battery is further reduced, and the battery still has good circulation capacity retention rate when discharged at a high rate.
In a specific embodiment, the electrolyte of the present invention further comprises a carbonate solvent and/or a carboxylate solvent. Wherein the carbonate solvent is selected from one or more of fluoro or unsubstituted Ethylene Carbonate (EC), propylene Carbonate (PC), dimethyl carbonate, diethyl carbonate (DEC) and methyl ethyl carbonate; the carboxylic ester solvent is selected from one or more of fluoro or unsubstituted propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isoamyl acetate, propyl Propionate (PP), ethyl Propionate (EP), methyl butyrate and ethyl n-butyrate.
The positive electrode current collector of the present invention may be selected from aluminum foils.
In a specific embodiment, the positive electrode active layer comprises, by mass, 80% -99.8% of a positive electrode active material, 0.1% -10% of a conductive agent, and 0.1% -10% of a binder. Preferably, the positive electrode active layer comprises 90 to 99.6 mass percent of positive electrode active material, 0.2 to 5 mass percent of conductive agent and 0.2 to 5 mass percent of binder.
In a specific embodiment, the positive electrode active layer of the present invention may further include a positive electrode active material such as lithium nickelate, lithium manganate, lithium nickel cobalt aluminate, lithium nickel manganate, lithium iron phosphate, ternary material, or the like, in addition to lithium cobaltate.
Further, doping of elements in the lithium cobaltate material may also be performed to enhance the internal structural stability of the lithium cobaltate material, wherein the doping elements are selected from one or more of Ti, mg, al, ni.
The conductive agent includes, but is not limited to, at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and carbon fiber.
The binder includes, but is not limited to, at least one of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.
The positive plate can be prepared by the following method: dispersing the positive electrode active material, the conductive agent and the binder in a solvent to obtain positive electrode active material layer slurry, coating the slurry on a positive electrode current collector, and drying to obtain the positive electrode plate.
The negative electrode sheet of the present invention comprises a negative electrode current collector and a negative electrode active material layer provided on at least one side surface of the negative electrode current collector, wherein the negative electrode current collector may be selected from copper foil.
In a specific embodiment, the negative electrode active layer comprises, by mass, 80% -99.8% of a negative electrode active material, 0.1% -10% of a conductive agent, and 0.1% -10% of a binder. Preferably, the negative electrode active layer comprises 90 to 99.6 mass percent of negative electrode active material, 0.2 to 5 mass percent of conductive agent and 0.2 to 5 mass percent of binder.
The negative electrode active material of the present invention includes, but is not limited to, at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon carbon material, and silicon oxygen material.
The conductive agent in the anode active layer includes, but is not limited to, at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and carbon fiber.
The binder in the negative active layer includes, but is not limited to, at least one of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.
The negative plate can be prepared by the following method: dispersing a negative electrode active material, a conductive agent and a binder in a solvent to form a negative electrode active slurry; and then coating the negative electrode active slurry on a negative electrode current collector, and drying and rolling to obtain the negative electrode plate.
The separator is used for separating the positive electrode plate from the negative electrode plate and providing a channel for lithium ion migration. The separator of the present invention may be selected from polypropylene separators, polyethylene separators, and the like.
In one embodiment, the battery is prepared by the following method: and sequentially stacking the positive plate, the diaphragm and the negative plate, enabling the diaphragm to be positioned between the positive plate and the negative plate, obtaining a battery cell through lamination or winding process, and then performing procedures of baking, liquid injection, formation, encapsulation and the like to obtain the battery.
The implementation of the invention has at least the following beneficial effects:
1) The electrolyte provided by the invention comprises the fluoroacetonitrile, wherein the extremely strong electronegativity of fluorine atoms enables the fluoroacetonitrile to react with an inert anode active material to form a stable covalent bond, so that the compatibility between the electrolyte and an anode is enhanced, the interface impedance is improved, the internal resistance of a battery is reduced, the fluoroacetonitrile also has lower viscosity and high dielectric constant, the conductivity of the electrolyte is improved, and further, the battery has good cycle performance, quick charge performance and storage performance.
2) The electrolyte provided by the invention adopts the combination of the fluoroacetonitrile and the polynitrile compound, so that the electrolyte has enough cyano groups and cobalt element in the positive electrode material are coordinated to form a protective film on the surface of the positive electrode, the structural stability of the lithium cobaltate material is enhanced, the thickness expansion of the battery caused by the phase change of the structure of the lithium cobaltate material under high voltage is inhibited, the side reaction of the positive electrode material and the electrolyte is avoided, and the gas production of the battery is inhibited.
3) According to the invention, the synergistic effect of the fluoroacetonitrile content W a, the polynitrile compound content W b and the cobalt element content W c in the electrolyte is researched to enable the electrolyte to meet a specific relational expression, so that the battery has excellent high-voltage resistance, cycle performance, storage performance and quick charge performance.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The battery provided by the present invention will be described in further detail by means of specific examples.
Unless otherwise indicated, reagents, materials and equipment used in the examples below are conventional in the art, conventional materials and conventional equipment, and are commercially available, and the reagents involved can also be obtained synthetically by methods conventional in the art.
Examples 1 to 25 and comparative examples 1 to 6
Examples 1 to 25 and comparative examples 1 to 6 provide a battery, and the preparation method is as follows:
1. Preparation of positive plate
Mixing positive active materials lithium cobaltate (LiCoO 2), polyvinylidene fluoride (PVDF), SP (super P) and Carbon Nano Tube (CNT) according to the mass ratio of 96:2:1.5:0.5, adding N-methyl pyrrolidone (NMP), and stirring under the action of a vacuum stirrer until the mixed system becomes positive active slurry with uniform fluidity; uniformly coating anode active slurry on two surfaces of an aluminum foil; and drying the coated aluminum foil, and then rolling and slitting to obtain the required positive plate.
Wherein, the lithium cobaltate consists of first particles with the particle diameter D50 of 30.7 mu m and second particles with the particle diameter D50 of 8.3 mu m according to the mass ratio of 4:1, wherein the mass percentage of the cobalt element W Co in the positive electrode active layer is 57.8%.
2. Preparation of negative electrode sheet
Taking a mixture of artificial graphite and silicon carbon in a mass ratio of 4:1 as a negative electrode active material, wherein the outer surface of the silicon carbon is provided with a coating layer, and the coating layer comprises carbon elements;
Uniformly mixing a negative electrode active substance, sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive carbon black and carbon nano tubes according to the mass ratio of 98.2:0.5:0.5:0.2:0.6, adding deionized water, and obtaining negative electrode active slurry under the action of a vacuum stirrer; uniformly coating the anode active slurry on two surfaces of a copper foil; and (3) airing the coated copper foil at room temperature, transferring to an 80 ℃ oven for drying for 10 hours, and then carrying out cold pressing and slitting to obtain the negative electrode plate, wherein the weight content of the element sodium in the negative electrode active material layer is 0.048%.
3. Preparation of electrolyte
In an argon-filled glove box (H 2O＜0.1ppm,O2 < 0.1 ppm), a sufficiently dry lithium salt was added to the mixture of solvent and additive, and dissolved to give an electrolyte.
Wherein the solvent is obtained by mixing EC, PC, EP, PP with the mass ratio of 1:1:2:6, the lithium salt in the electrolyte is lithium hexafluorophosphate, and the mass content W d is 15%.
The additives included 8% FEC and other additives, the types and mass content of which are listed in table 1.
4. Preparation of lithium ion batteries
Laminating the positive plate in the step 2, the negative plate in the step 3 and the diaphragm (the PP diaphragm with the diameter of 9 mu m) in the order of the positive plate, the diaphragm and the negative plate, and then winding to obtain a battery cell; and (3) placing the battery cell in an outer packaging aluminum foil, injecting the electrolyte in the step (1) into the outer packaging aluminum foil, and performing the procedures of vacuum packaging, standing, formation, shaping, sorting and the like to obtain the lithium ion battery.
TABLE 1
Examples 26 to 32
Examples 26 to 32 provided a battery substantially identical to example 1 except that in the preparation of the electrolyte, the mass content of the fluoroacetonitrile added was 7%, and in the preparation of the positive electrode sheet, lithium cobaltate of example 26 was prepared from first particles having a particle diameter D50 of 30.7 μm and second particles having a particle diameter D50 of 8.3 μm in a mass ratio of 4:1, the lithium cobaltate of example 27 comprises only first particles having a particle diameter D50 of 30.7 μm, the lithium cobaltate of example 28 comprises only second particles having a particle diameter D50 of 8.3 μm, and the lithium cobaltate of example 29 comprises, in mass ratio, 4:1, the lithium cobaltate of example 30 was obtained by mixing first particles having a particle diameter D50 of 35 μm and second particles having a particle diameter D50 of 5 μm in a mass ratio of 4:1, the lithium cobaltate of example 31 was obtained by mixing first particles having a particle diameter D50 of 30.7 μm and second particles having a particle diameter D50 of 3 μm in a mass ratio of 4:1, the lithium cobaltate of example 32 was obtained by mixing first particles having a particle diameter D50 of 40 μm and second particles having a particle diameter D50 of 8.3 μm in a mass ratio of 4:1, the specific variation factors are listed in table 2.
TABLE 2
Test case
1. Cycle performance
A. Capacity retention rate of 800 weeks at 25 deg.c
The battery is subjected to charge-discharge circulation for 800 weeks at 25 ℃ according to the multiplying power of 5C within the charge-discharge cut-off voltage range of 3.0-4.55V, the discharge capacity of the 1 st week is tested to be x1mAh, and the discharge capacity of the 800 th week is tested to be y1mAh; the capacity retention at 25℃for 800 weeks was calculated by y1/x 1X 100%.
B. Capacity retention rate of 800 weeks at 45 deg.c
The battery is subjected to charge-discharge circulation for 800 weeks at 45 ℃ according to the multiplying power of 5C within the charge-discharge cut-off voltage range of 3.0-4.55V, the discharge capacity of the 1 st week is measured as m 1mAh, and the discharge capacity of the 800 circles is measured as n1mAh; the cycle capacity retention at 45℃for 800 weeks was calculated from n 1/m1X100%.
2. Rate capability
The testing method comprises the following steps: the battery after the formation of the capacity is firstly stood for 10min, then discharged to a lower limit voltage of 3V by 0.2C, the discharged discharge capacity is marked as an initial discharge capacity C0, the battery is stood for 10min, then charged to an upper limit voltage of 4.55V by 0.7C, then charged to a cut-off of 0.025C at the upper limit voltage, finally discharged to a lower limit voltage of 3.0V by 5C current, the discharge capacity C1 of the battery is recorded, and the discharge rate capacity retention rate of 5C is obtained through calculation by C1/C0.
3. High temperature storage performance
The testing method comprises the following steps: at room temperature, recording the initial thickness T1 of the battery after capacity division, then placing the full-charge battery in an incubator at 85 ℃ for 15 days, taking out and cooling to return to room temperature after storage, recording the thickness T2 of the battery, and obtaining the thickness expansion rate of the battery at 85 ℃ for 15 days through calculation of T2/T1 multiplied by 100 percent.
The above test results are listed in table 3.
TABLE 3 Table 3
1) From comparison of examples 1, 2,4, 7, 22, 26, when the content of fluoroacetonitrile in the electrolyte is too small, less than 10%, the 25 ℃ and 45 ℃ cycle performance, the quick charge performance, and the high temperature storage performance of the battery are all deteriorated.
2) From comparison of examples 1,3, 5, and 6, it can be seen that the polynitrile compound content in the most preferred range of 4% to 6% provides a battery with more excellent overall performance, but when it is < 4% or > 7%, the battery cycle, rate and high temperature storage performance are slightly lowered.
3) From the comparison of examples 1, 8, 9, 23, 24 and 25, it is apparent that the use of different kinds of polynitrile compounds can provide batteries with excellent high-low temperature cycle performance, fast charge performance and high temperature storage performance.
4) From the comparison of examples 1 and 10 to 18, the cyclic sulfonate compounds shown in the formula I with different substitution types can be added to improve the high-low temperature cycle performance, the fast charge performance and the high-temperature storage performance of the battery, and especially the fast charge performance is improved remarkably.
5) As can be seen from the comparison of examples 1, 19 to 21, when the content of the cyclic sulfonate compound represented by formula I is less than 0.5% or more than 10%, deterioration of the high-low temperature cycle performance, the fast charge performance and the high-temperature storage performance of the battery occurs.
6) From the comparison of example 1 and comparative examples 1 to 3, it is apparent that the high and low temperature cycle performance, the fast charge performance and the high temperature storage performance of the battery are remarkably poor when the fluoroacetonitrile or the polynitrile compound is not added to the electrolyte.
7) As can be seen from comparative examples 4 to 6, when the content Wa of fluoroacetonitrile, the content Wb of the polynitrile compound, and the content of Co element in the positive electrode active layer were not satisfied by 0.12 to 1.12, the high-low temperature cycle performance, the fast charge performance, and the high temperature storage performance of the battery also exhibited significant deterioration, and particularly when the cyclic sulfonate compound represented by formula I was not added in comparative example 6, the fast charge performance was more significant deterioration.
8) From the comparison of examples 26 to 28, the lithium cobaltate material with the size and the particle diameter matched with the first particle and the second particle is favorable for leading the battery to have more excellent 25 ℃ cycle performance, 45 ℃ storage performance, 5C discharge performance and high temperature storage performance; as can be seen from the comparison of examples 26, 29 to 32, when the first particles used had too large a D50 particle diameter, or the second particles had too small a D50 particle diameter, or the ratio N of the two particle diameters D50 was not in the range of 3 to 65, or W a/N.ltoreq.0.012, the high-low temperature cycle performance, 5C rate performance, 85℃high temperature storage performance of the battery were inferior to those satisfying the above conditions.
The above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims (10)

1. The battery comprises a positive plate, a negative plate, a diaphragm and electrolyte, and is characterized in that the positive plate comprises a positive current collector and a positive active layer arranged on at least one side surface of the positive current collector, and the positive active layer comprises a lithium cobaltate material; the mass percentage of cobalt element in the positive electrode active layer is W Co;
The electrolyte comprises fluoroacetonitrile and polynitrile compounds; based on the mass of the electrolyte, the mass percentage of the fluoroacetonitrile is W a, and the mass percentage of the polynitrile compound is W b;
Wherein, W a+Wb)/WCo is more than or equal to 0.12 and less than or equal to 1.12.
2. The battery of claim 1, wherein (W a 2-Wb 2)/Wa +.0.80).
3. The battery according to claim 1 or 2, characterized in that W a% or less than 85%, preferably 10% or less than W a% or less than 60%;
And/or, W b is more than or equal to 2% and less than or equal to 10%, preferably, W b is more than or equal to 4% and less than or equal to 6%;
And/or, 35% or less than or equal to W Co% or less than or equal to 65%, preferably, 54.8% or less than or equal to W Co% or less than or equal to 63.1%.
4. A battery according to any one of claims 1-3, wherein the electrolyte further comprises an additive of formula I:
A-B-C formula I;
In the formula I, A is selected from a structure shown in a formula Ia or a formula Ib, B is selected from a single bond, H or a structure shown in a formula Ic, and C is selected from H, a structure shown in a formula Id or a structure shown in Ie;
in the formula Ia, X 1 is selected from-O-or-CH 2-,n1 and is an integer between 0 and 4;
In the formula Ib, X 2 is selected from-O-or-CH 2-,n2 and is an integer between 0 and 3;
In the formula (Ic), X 3 and X 4 are each independently selected from-O-or-CH 2-,Y1 is selected from-C (O) -or-S (O) 2 -;
In the formula Id, X 5 and X 6 are each independently selected from-O-or-CH 2-,Y2 is selected from-C (O) -or-S (O) 2-,n3 and are integers between 0 and 4;
In formula Ie, X 7 is selected from-O-or-CH 2-,n4 and is an integer between 0 and 3.
5. The battery of claim 4, wherein the additive of formula I is selected from one or more of the following compounds:
6. The battery according to claim 4 or 5, wherein the electrolyte further comprises lithium salt, and the mass percentage of the lithium salt is W d, and the mass percentage of the additive shown in formula I is W c, wherein W d/Wc is equal to or greater than 3, based on the mass of the electrolyte.
7. The battery of claim 6, wherein 0.5% to 10% W c%;
And/or, 5% or less W d% or less 30%, preferably 10% or less W d% or less 20%.
8. The battery of any one of claims 1-7, wherein the lithium cobaltate material comprises first particles and second particles, the ratio of D50 particle sizes of the first particles and the second particles being N;
Wherein N is more than or equal to 3 and less than or equal to 6.5.
9. The battery of claim 8, wherein the D50 particle size of the first particles is 15-35 μιη; and/or the second particles have a D50 particle size of 5 to 20 μm.
10. The battery of claim 7, wherein W a/N is ≡0.012.
CN202410862611.0A 2024-06-28 2024-06-28 Battery cell Pending CN118589019A (en)

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