CN117117324A - Lithium ion battery - Google Patents

Lithium ion battery Download PDF

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Publication number
CN117117324A
CN117117324A CN202311271360.0A CN202311271360A CN117117324A CN 117117324 A CN117117324 A CN 117117324A CN 202311271360 A CN202311271360 A CN 202311271360A CN 117117324 A CN117117324 A CN 117117324A
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lithium
positive electrode
ion battery
lithium ion
equal
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林雄贵
向晓霞
皮琛琦
范双显
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Shenzhen Capchem Technology Co Ltd
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Shenzhen Capchem Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • 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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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Inorganic Chemistry (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Physics & Mathematics (AREA)
  • Materials Engineering (AREA)
  • Secondary Cells (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery with improved quick charge performance and cycle life. The lithium ion battery comprises a positive electrode, a negative electrode and a nonaqueous electrolyte; the positive electrode includes a positive electrode material layer including a positive electrode active material; the nonaqueous electrolyte comprises lithium salt, an organic solvent and an additive, wherein the additive comprises lithium difluorophosphate and boron-containing lithium salt; the working cut-off voltage of the lithium ion battery is more than or equal to 4.3V; the lithium ion battery meets the following conditions: the (B+C) multiplied by D/H is more than or equal to 0.02 and less than or equal to 0.5, B is more than or equal to 0.05 and less than or equal to 1.5,0.05, C is more than or equal to 1.5, D is more than or equal to 2.5 and less than or equal to 6.5, and H is more than or equal to 15 and less than or equal to 40. According to the lithium ion battery disclosed by the invention, the CEI interface film rich in LiF, P=O groups and B-O groups is formed on the positive electrode by utilizing lithium difluorophosphate and boron-containing lithium salt, and the electrolyte infiltration effect and the film forming condition are influenced by regulating and controlling the particle size and the porosity of the positive electrode active material, so that the film forming quality of the positive electrode is improved, the impedance is reduced, the migration rate of lithium ions is improved, the positive electrode is protected, the volume expansion and the structural damage of the positive electrode are restrained, and the quick charging capacity and the cycle life of the lithium ion battery are optimized.

Description

Lithium ion battery
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery with improved quick charge performance and cycle life.
Background
Electrochemical energy storage is widely used in portable electronic products and Electric Vehicles (EVs) to limit the influence of climate change air pollution, and the requirements and the dependence on lithium ion batteries become higher than ever before. However, compared with the traditional fuel vehicle, the problems of mileage anxiety, long charging time and the like become main problems which obstruct the development of the electric vehicle. Therefore, the improvement of battery energy density and quick charge capability is a popular development goal of battery manufacturers and whole vehicle factories.
Electrode polarization is a major contributor to the battery's ability to charge quickly, and its factors mainly include the diffusion rate of lithium ions in the active material, the transport of lithium ions in the electrolyte, and the charge transfer kinetics at the electrode/electrolyte interface. Common strategies for improvement include the introduction of electrolytes with high ionic conductivity, weak solvation, and the construction of stable solid electrolyte interface/positive electrolyte interface. The electrolyte component not only can adjust the electrode/electrolyte interface, but also can influence the performance of the battery, and mainly comprises capacity, internal resistance, multiplying power charge and discharge performance and the like. Increasing the ionic conductivity of the electrolyte is beneficial to reducing the solvation and desolvation activation energy of lithium ions and is beneficial to realizing quick charge. Therefore, how to improve the ion conductivity and form an interfacial film for an electrode/electrolyte through which lithium ions rapidly pass by controlling the electrolyte composition is important.
Methods for increasing the energy density of a battery are mainly to increase the compacted density to increase the mass of active material per unit volume and to increase the positive electrode charge cutoff voltage. However, increasing the compaction density can lead to the reduction of the porosity of the electrode, the liquid retention of the battery can also be reduced, the electrolyte is difficult to permeate at the interface of the low-porosity pole piece, so that the contact internal resistance between the electrolyte and the electrode is increased, the polarization is increased, the lithium precipitation phenomenon is easy to occur under the condition of fast charging and high current, meanwhile, the heat generation of the battery is obvious, and the thermal runaway is easy to be caused. The positive electrode charging cut-off voltage is increased, the activity of a positive electrode material can be improved, the positive electrode phase change process can gradually shift to high voltage under the influence of internal resistance increase in the circulation process, and some particles which are in a higher lithiation degree can be continuously charged due to dynamic driving, so that the particles are in a higher lithium removal state, further irreversible phase change occurs, the material crystal lattice is easier to break, a series of problems of transition metal dissolution, oxygen release, aggravation, electrolyte reaction and the like are caused, and the circulation performance is rapidly reduced.
Therefore, in response to the requirements of rapid battery charging and energy density, there is an urgent need to develop a high-performance battery having low impedance at high voltage, satisfying rapid battery charging, and having good cycle performance.
Disclosure of Invention
In order to solve the technical problems, the invention provides a lithium ion battery with improved quick charge performance and cycle life.
The invention adopts the following technical scheme:
a lithium ion battery comprises a positive electrode, a negative electrode and a nonaqueous electrolyte; the positive electrode includes a positive electrode material layer containing a positive electrode active material including Li 1+x Ni a Co b M’ 1-a-b O 2-y A y Wherein x is more than or equal to 0.1 and less than or equal to 0.2,0<a<1，0≤b<1，0<a+b<1，0≤y<0.2, m' comprises one or more of Mn, al, sr, mg, ti, ca, zr, zn, si, fe, ce, nb, ga, cu, sn, cr, sr, W or V, a comprises one or more of S, N, F, B, cl, br and I; the nonaqueous electrolytic solution comprises a lithium salt, an organic solvent and an additive, wherein the additive comprises lithium difluorophosphate and a boron-containing lithium salt, and the boron-containing lithium salt comprises lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate (LiBF) 4 ) And at least one of lithium bis (oxalato) borate (LiBOB); the working cut-off voltage of the lithium ion battery is more than or equal to 4.3V; the lithium ion battery meets the following conditions:
0.02-B+C multiplied by D/H-0.5, B-1.5,0.05-C-1.5, D-6.5, H-40 and B-0.05-1.5,0.05-C-2.5;
wherein B is the mass percentage of lithium difluorophosphate in the nonaqueous electrolyte, and the unit is wt%;
c is the mass percentage of boron-containing lithium salt in the nonaqueous electrolyte, and the unit is wt%;
d is the median particle diameter of the positive electrode active material, and the unit is mu m;
h is the porosity of the positive electrode material layer in%.
According to the invention, lithium difluorophosphate and boron-containing lithium salt are used in combination to construct the positive electrode interface protective film rich in LiF, P=O groups and B-O groups, so that the lithium ion migration rate is improved, the positive electrode is protected, the volume expansion and structural damage of the positive electrode are inhibited, and the quick charge cycle performance is optimized. If the film formation is insufficient, the electrolyte is continuously oxidized and decomposed at the positive electrode, the impedance is increased, and the battery performance is rapidly deteriorated; the film formation is too thick, consuming active lithium, increasing resistance and deteriorating the rapid charging performance. Meanwhile, the lithium salt type additive can cause larger increase of the viscosity of the electrolyte, which is not beneficial to the infiltration of the electrolyte and the transmission of lithium ions, so that when the dosage of the lithium difluorophosphate and the boron-containing lithium salt is increased, the porosity of the positive electrode material layer is required to be increased, the infiltration of the electrolyte is facilitated, the difficulty of the transmission of the lithium ions is reduced, the requirement of quick charge is met, and the lithium precipitation is avoided; in addition, when the particle size of the positive electrode active material is reduced, the specific surface area is increased, and the amount of lithium difluorophosphate and boron-containing lithium salt to be consumed is correspondingly increased, otherwise, the interface of the positive electrode interface film is easy to generate defects or nonuniform deposition, so that sudden water jump is caused in the battery circulation process, especially in the high-temperature 4C-stage charge cycle, the interface reaction is aggravated, the impedance is obviously increased, the temperature rise effect is aggravated, and the circulation is faster. The inventor finds that when the mass percent B of lithium difluorophosphate, the mass percent C of boron-containing lithium salt, the median particle diameter D of the positive electrode active material and the porosity H of the positive electrode material layer meet the conditions of 0.02-0.5 (B+C) x D/H, B-0.05-1.5,0.05-1.5, D-2.5-6.5 and H-15-40, dynamic balance can be maintained, the wetting effect and film forming quality of the electrolyte are ensured, and a good positive electrode interface film is formed, and the quick charge performance and the cycle life of the battery are improved.
Preferably, the lithium ion battery satisfies the following conditions: the (B+C) multiplied by D/H is more than or equal to 0.05 and less than or equal to 0.4.
In some specific embodiments of the invention, the additive lithium difluorophosphate can participate in film formation at the negative electrode to form an inorganic interface film rich in LiF, and also participate in film formation at the positive electrode, resist high pressure, inhibit the electrolyte from oxidative decomposition at the positive electrode, protect the stability of the positive electrode, inhibit transition metal ion crosstalk and inhibit diving. The lithium difluorophosphate may be present in an amount ranging from 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.4wt%, 0.5wt%, 0.75wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.2wt%, 1.3wt%, 1.5wt% or any value above. The lithium difluorophosphate is affected by poor solubility, and the lithium difluorophosphate accounts for 0.15-1 wt% of the nonaqueous electrolyte by combining film forming consumption.
In some specific embodiments of the invention, the boron-containing lithium salt has a higher HOMO energy level and better thermal stability, and is preferentially decomposed on the positive electrode to form an interfacial film rich in borate, so that the electrochemical performance of the high-voltage positive electrode is improved, and meanwhile, the aluminum foil can be passivated to inhibit corrosion. The content of the boron-containing lithium salt may be 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.4wt%, 0.5wt%, 0.75wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.2wt%, 1.3wt%, 1.5wt% or a range composed of any of the above values. The boron-containing lithium salt is preferable to the solvent decomposition, so that the film forming consumption is larger, and more preferably, the boron-containing lithium salt accounts for 0.15-1.2 wt% of the nonaqueous electrolyte, so as to ensure the film forming quality.
Preferably, the boron-containing lithium salt comprises at least one of lithium difluoroborate, lithium tetrafluoroborate and lithium bisoxalborate; more preferably, the boron-containing lithium salt includes at least one of lithium difluorooxalato borate and lithium tetrafluoroborate.
Because electrolyte components can be consumed on the surface of the positive electrode material to form a passivation film, theoretically, the smaller the particle size of the active material is, the larger the specific surface area is, the larger the contact reaction area with the electrolyte is, and a sufficient amount of additives are needed to ensure uniform film formation at the interface, so that the solvolysis at the positive electrode interface and the structural change of the positive electrode active material are inhibited under high voltage. Meanwhile, the particle size is reduced, so that the diffusion path of lithium ions in the battery can be shortened, and the electrochemical reaction activity of the lithium ion battery is enhanced; however, when the particle size of the positive electrode active material is too small, the agglomeration of particles is increased, and the solid-phase diffusion coefficient of lithium ions is rather lowered, resulting in an increase in the internal resistance of the battery. Accordingly, the present invention defines a range in which the median particle diameter of the positive electrode material is 2.5 μm to 6.5 μm, specifically, the median particle diameter is 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm or any value above, based on the selected contents of lithium difluorophosphate and the boron-containing lithium salt. The smaller particle size of the positive electrode active material can improve the long cycle performance and impedance of the lithium ion battery, but film forming protection is needed, otherwise, the exposed active surface can cause serious decomposition of electrolyte, aggravate ion shuttle effect, cause dissolution of transition metal and decay of battery capacity. Preferably, the median particle diameter D of the positive electrode active material is 3 μm to 5 μm.
The testing method of the median particle diameter D of the positive electrode active material comprises the following steps: soaking and cleaning a positive plate by DMC (dimethyl carbonate), placing the positive plate in a glove box, carrying out vacuum drying for 24 hours, taking a sample in a middle area, carrying out SEM test, selecting an accelerating voltage of 10kV, a working distance of 13mm, an amplifying multiple of 5k and a scale of 10 mu m, shooting the test to obtain a picture with the size of 25 mu m multiplied by 25 mu m, requiring more complete active material particles in the picture to be more than or equal to 30, selecting the maximum particle size in a picture to carry out particle size statistics of a positive material layer, accumulating the maximum particle values of ten effective pictures, deleting the maximum value and the minimum value, and taking the average value to obtain a median particle size D, wherein the rest numbers are named as R1, R2, … … and R8 respectively, and the calculation method is as follows:
median diameter d= (longest diameter r1+ … … +longest diameter R8)/8.
When the porosity of the positive electrode material layer is too low, the interface impedance is increased, which is not beneficial to the transmission of lithium ions and has poor quick charge performance; when the porosity is too high, the energy density is not improved, and meanwhile, harmful impurities can possibly pass through the porous ceramic material to harm the battery performance. The invention limits the porosity H of the positive electrode material layer to 15% -40%, the interface impedance is at a lower level, the porosity degree is convenient for electrolyte infiltration, simultaneously, the lithium ion transmission is also facilitated, the quick charge performance is better, and the volume energy density is considered. Specifically, the porosity H of the positive electrode material layer is in a range of 15%, 16%, 18%, 20%, 22%, 24%, 25%, 27%, 28%, 30%, 32%, 35%, 38%, 40% or any of the above values. When the viscosity of the electrolyte is lower and the conductivity is higher, the porosity of the positive electrode material layer can be properly reduced under the condition of meeting the electrolyte infiltration, and the quick charge performance of the battery is not reduced. Therefore, based on the selected content of lithium difluorophosphate and boron-containing lithium salt, etc., it is preferable that the porosity H of the positive electrode material layer is 16% to 30%; more preferably, the porosity H of the positive electrode material layer is 22% to 30%.
Further, the additive also comprises vinyl sulfate, and the lithium ion battery meets the following conditions:
0.1≤C/E≤13，0.01≤E≤2.5；
wherein E is the mass percentage of the ethylene sulfate to the nonaqueous electrolyte, and the unit is wt%.
The vinyl sulfate mainly participates in the film formation of the negative electrode, and the film forming component mainly comprises a sulfur-containing organic compound, so that the high-temperature performance of the battery can be improved, but the electrode interface film can be thickened, and the interface impedance of the battery is increased. The invention defines a range in which the mass percentage E of the vinyl sulfate in the nonaqueous electrolyte is 0.01wt% to 2.5wt%, specifically, 0.01wt%, 0.03wt%, 0.06wt%, 0.09wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.4wt%, 0.5wt%, 0.75wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.5wt%, 1.8wt%, 2wt%, 2.5wt% or any of the above. Considering the safety problems caused by impedance and gas production comprehensively, preferably, the mass percentage E of the ethylene sulfate in the nonaqueous electrolyte is 0.03-1.5 wt%.
The vinyl sulfate not only forms a film on the negative electrode and improves high-temperature performance, but also can participate in the film formation of the positive electrode. The CEI film formed by the vinyl sulfate film forming on the positive electrode is mainly a sulfur-containing organic compound, which can increase the impedance of the battery, is unfavorable for the transmission and diffusion of lithium ions, does not resist high pressure and is easy to decompose. According to the invention, the vinyl sulfate and the boron-containing lithium salt are mixed to be used as additives, the content of the vinyl sulfate and the boron-containing lithium salt is regulated to be less than or equal to 0.1 and less than or equal to 13, the organic components and the inorganic components of the positive electrode interface film are in a proper proportion, and the LiF and the B-O inorganic components generated by combining the sulfur-containing organic compound and the boron-containing lithium salt in the positive electrode are combined to inhibit the impedance from increasing, and meanwhile, the high-temperature performance of the battery can be improved. If the proportion of the boron-containing lithium salt is too high, the inorganic component of the positive electrode interface film covers the sulfur-containing organic compound component, so that the film is thickened, and the high-temperature storage performance cannot be improved; if the proportion of the boron-containing lithium salt is too low, the film formation is insufficient, the sulfur-containing organic compound is continuously decomposed, the interface is continuously deteriorated, and the battery performance decay is accelerated.
Specifically, the content ratio C/E of vinyl sulfate and boron-containing lithium salt is 0.1, 0.3, 0.5, 0.8, 1, 1.5,2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13; preferably, the content ratio of vinyl sulfate and boron-containing lithium salt satisfies the following conditions: C/E is more than or equal to 0.5 and less than or equal to 10.
In some embodiments, the positive electrode active material includes LiNi 0.5 Co 0.2 Mn 0.3 O 2 、LiNi 0.5 Co 0.2 Mn 0.2 Al 0.1 O 2 、LiNi 0.6 Co 0.1 Mn 0.3 O 2 、LiNi 0.6 Co 0.2 Mn 0.2 O 2 、LiNi 0.65 Mn 0.35 O 2 、LiNi 0.75 Mn 0.25 O 2 、LiNi 0.7 Co 0.1 Mn 0.2 O 2 、LiNi 0.8 Co 0.05 Mn 0.15 O 2 、LiNi 0.8 Co 0.1 Mn 0.1 O 2 、LiNi 0.8 Co 0.15 Al 0.05 O 2 、LiNi 0.9 Co 0.05 Mn 0.05 O 2 One or more of the following.
In some embodiments, the nonaqueous electrolytic solution further includes an auxiliary additive including at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, a phosphate compound, a borate compound, and a nitrile compound;
preferably, the cyclic sulfate compound is at least one selected from the group consisting of vinyl 4-methyl sulfate and propylene sulfate;
the sultone compound is at least one selected from 1, 3-propane sultone, 1, 4-butane sultone and propenyl-1, 3-sultone;
the cyclic carbonate compound is selected from at least one of ethylene carbonate, methylene ethylene carbonate, fluoroethylene carbonate (FEC), trifluoromethyl ethylene carbonate, bis-fluoroethylene carbonate and a compound shown in the following structural formula 1:
in the structural formula 1, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 Each independently selected from one of a hydrogen atom, a halogen atom, a C1-C5 group;
more preferably, the compound represented by the structural formula 1 includes at least one of the following compounds 1-1 to 1-6:
the phosphate compound is at least one selected from tris (trimethylsilane) phosphate (TMSP), tris (triethylsilane) phosphate and a compound shown in the following structural formula 2:
in the structural formula 2, R 31 、R 32 、R 33 Each independently selected from the group consisting of C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halogenated hydrocarbon groups, -Si (C) m H 2m+1 ) 3 M is a natural number of 1 to 3, and R 31 、R 32 、R 33 At least one of them is an unsaturated hydrocarbon group; more preferably, the compound of formula 2 comprises tripropylethyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphateAt least one of acid esters, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2, 2-trifluoroethyl phosphate, dipropargyl-3, 3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2, 2-trifluoroethyl phosphate, diallyl-3, 3-trifluoropropyl phosphate, diallyl hexafluoroisopropyl phosphate;
the borate compound is at least one selected from tri (trimethylsilane) borate and tri (triethylsilane) borate;
the nitrile compound is at least one selected from succinonitrile, glutaronitrile, ethylene glycol bis (propionitrile) ether, hexanedinitrile, adiponitrile, pimelic nitrile, suberonitrile, nonyldinitrile and decyldinitrile.
In some embodiments, the auxiliary additive is present in an amount of 0.01wt% to 10wt% based on 100% total mass of the nonaqueous electrolyte. Preferably, the content is 0.1-5%; more preferably, the content is 0.1% -2%. Specifically, the content of any optional substance in the auxiliary additive may be 0.01%, 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%.
In some embodiments, the organic solvent includes at least one of an ether solvent, a nitrile solvent, a carbonate solvent, a carboxylate solvent, and a sulfone solvent.
In a preferred embodiment, the ether solvent includes a cyclic ether or a chain ether, and the cyclic ether may be specifically but not limited to at least one of 1, 3-Dioxolane (DOL), 1, 4-Dioxane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH 3-THF), 2-trifluoromethyl tetrahydrofuran (2-CF 3-THF); the chain ether may be specifically but not limited to at least one of Dimethoxymethane (DMM), 1, 2-Dimethoxyethane (DME), diglyme (TEGDME). The nitrile solvent may be, but not limited to, at least one of acetonitrile, glutaronitrile, malononitrile. The carbonate solvent comprises cyclic carbonate or chain carbonate, and the cyclic carbonate can be at least one of Ethylene Carbonate (EC), propylene Carbonate (PC), gamma-butyrolactone (GBL) and Butylene Carbonate (BC); the chain carbonate may be, but not limited to, at least one of dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC). The carboxylic acid ester solvent may be, but not limited to, specifically at least one of Methyl Acetate (MA), ethyl Acetate (EA), propyl acetate (EP), butyl acetate, propyl Propionate (PP), butyl propionate. The sulfone-based solvent includes cyclic sulfone and chain sulfone, and is preferably a compound having usually 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms, in the case of cyclic sulfone, and usually 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms, in the case of chain sulfone.
In some embodiments, the lithium salt is selected from LiPF 6 、LiTFSI、LiDFOP、LiSbF 6 、LiAsF 6 、LiN(SO 2 C 2 F 5 ) 2 、LiC(SO 2 CF 3 ) 3 、LiClO 4 、LiAlCl 4 、LiCF 3 SO 3 、LiSO 3 F、Li 2 B 10 Cl 10 One or more of lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, lithium chloroborane, lithium lower aliphatic carboxylic acid having 4 or less carbon atoms, lithium tetraphenylborate.
In a specific embodiment, the total molar content of the lithium salt is 0.1mol/L to 4mol/L. In a preferred embodiment, the total molar content of lithium salt is 0.5mol/L to 2.5mol/L. Specifically, the total molar content of the lithium salt may be 0.5mol/L, 0.55mol/L, 0.6mol/L, 0.65mol/L, 0.7mol/L, 0.8mol/L, 0.85mol/L, 0.9mol/L, 0.95mol/L, 1.0mol/L, 1.1mol/L, 1.15mol/L, 1.2mol/L, 1.3mol/L, 1.4mol/L, 1.45mol/L, 1.5mol/L, 1.6mol/L, 1.7mol/L, 1.8mol/L, 1.9mol/L, 2.0mol/L, 2.1mol/L, 2.2mol/L, 2.3mol/L, 2.4mol/L or 2.5mol/L.
In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent.
The positive electrode binder includes thermoplastic resins such as polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, polypropylene, and the like; an acrylic resin; and one or more of styrene butadiene rubber.
The positive electrode conductive agent comprises one or more of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.
In some embodiments, the negative electrode comprises a negative electrode material layer comprising a negative electrode active material comprising one or more of a carbon-based negative electrode, a silicon-based negative electrode, a tin-based negative electrode, a lithium negative electrode. Wherein the carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, and the like; the silicon-based anode may include a silicon material, an oxide of silicon, a silicon-carbon composite material, a silicon alloy material, or the like; the tin-based negative electrode may include tin, tin carbon, tin oxygen, and tin metal compounds; the lithium negative electrode may include metallic lithium or a lithium alloy. The lithium alloy may specifically be at least one of a lithium silicon alloy, a lithium sodium alloy, a lithium potassium alloy, a lithium aluminum alloy, a lithium tin alloy, and a lithium indium alloy.
In some embodiments, the negative electrode further comprises a negative electrode current collector, and the negative electrode material layer is disposed on a surface of the negative electrode current collector. The material of the negative electrode current collector may be the same as that of the positive electrode current collector, and will not be described again.
In some embodiments, the negative electrode material layer further comprises a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder and the negative electrode conductive agent are blended to obtain the negative electrode material layer. The negative electrode binder and the negative electrode conductive agent may be the same as the positive electrode binder and the positive electrode conductive agent, respectively, and will not be described again here.
In some embodiments, the lithium ion battery further comprises a separator, wherein the separator is positioned between the positive electrode and the negative electrode.
The membrane can be an existing conventional membrane, and can be a ceramic membrane, a polymer membrane, a non-woven fabric, an inorganic-organic composite membrane and the like, including but not limited to a membrane such as single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP/PE, double-layer PP/PP, and three-layer PP/PE/PP.
According to the lithium ion battery disclosed by the invention, lithium difluorophosphate and boron-containing lithium salt are selected as electrolyte additives, and the median particle size of an anode active material and the porosity of an anode material layer are limited, when the lithium ion battery meets the relation of 0.02-0.5 (B+C) x D/H, B is more than or equal to 0.05-1.5,0.05-C is more than or equal to 1.5, D is more than or equal to 2.5-6.5, H is more than or equal to 15-40, a CEI interface film rich in LiF, P=O groups and B-O groups is formed on the anode by utilizing the lithium difluorophosphate and the boron-containing lithium salt, and the electrolyte infiltration effect and the film forming condition are influenced by regulating the particle size and the porosity of the anode active material, so that the film forming quality of the anode is improved, the impedance is reduced, the migration rate of lithium ions is improved, the anode is protected, the volume expansion and the structural damage of the anode are inhibited, the quick charge capacity and the cycle life of the lithium ion battery are optimized, and the high-temperature storage performance is also considered.
Detailed Description
The following description of the embodiments of the present invention will clearly and completely describe the technical solutions of the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, 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 fall within the scope of the invention.
Example 1
The preparation method of the lithium ion battery in the embodiment comprises the following steps:
1) Preparation of electrolyte:
the Ethylene Carbonate (EC) and the methyl ethyl carbonate (EMC) are formed by volumeThe ratio EC: emc=3:7 was mixed, and then lithium hexafluorophosphate (LiPF was added 6 ) The mass percentage of the lithium difluorophosphate, the boron-containing lithium salt and other additives in the electrolyte is shown in table 1 based on the total weight of the electrolyte as 100 percent.
2) Preparation of positive electrode:
the positive electrode active material LiNi was mixed in a mass ratio of 95:2.5:0.5:2 0.6 Co 0.2 Mn 0.2 O 2 Conductive carbon black Super-P, carbon nanotubes and a binder polyvinylidene fluoride (PVDF) which are then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry is uniformly coated on two sides of an aluminum foil, and the aluminum outgoing line is welded by an ultrasonic welding machine to obtain the positive electrode, wherein the porosity of the positive electrode material layer after vacuum drying and the median particle size of the positive electrode active material are shown in table 1.
3) Preparation of the negative electrode:
the negative electrode active material artificial graphite, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94.7:1.5:1.4:2.4, and then dispersed in deionized water to obtain a negative electrode slurry. Coating the slurry on two sides of a copper foil, drying, calendaring and vacuum drying, and welding a nickel outgoing line by an ultrasonic welder to obtain a negative electrode, wherein the thickness of the polar plate is 120-150 mu m.
4) Preparation of the battery cell:
and placing three layers of diaphragms with the thickness of 20 mu m between the anode and the cathode, then laminating and assembling a sandwich structure formed by the anode, the cathode and the diaphragms into a soft-package battery, respectively welding outgoing lines of the anode and the cathode on corresponding positions of a cover plate, and welding the cover plate and a metal shell into a whole by using a laser welding machine to obtain the battery cell to be injected with the liquid.
5) And (3) filling and forming the battery cell:
in a glove box with the dew point controlled below-40 ℃, the prepared electrolyte is injected into a battery cell, and is subjected to vacuum encapsulation and is kept at 45 ℃ for 48 hours.
And then carrying out hot pressing formation of primary charging according to the following steps: at 45 ℃,0.05C constant current charge is carried out for 3 hours, the pressure is 3kg/cc,0.1C constant current charge is carried out for 2 hours, the pressure is 5kg/cc, and 0.2C constant current charge is carried out for 2 hours, and the pressure is 5kg/cc. Resting for 48h at 45 ℃. Sealing in vacuum for the second time, charging to 4.35V with constant current of 0.5C, charging to 0.05C with constant voltage, standing for 5min, discharging to 3.0V with constant current of 0.5C to obtain a kind of LiNi 0.6 Co 0.2 Mn 0.2 O 2 Artificial graphite lithium ion battery.
Examples 2 to 38 and comparative examples 1 to 18
This example and comparative example are used to comparatively illustrate the disclosed lithium ion battery, and include most of the operating steps described in example 1 above, except that: the mass percentages and types of the lithium difluorophosphate, the boron-containing lithium salt and the auxiliary additive in the nonaqueous electrolyte are shown in table 1, and the types of the positive electrode active materials, the porosities of the positive electrode material layers and the median particle sizes of the positive electrode active materials are shown in table 1, based on 100% of the total weight of the nonaqueous electrolyte.
The lithium ion batteries prepared in each example and comparative example were subjected to performance testing as follows:
1. high Wen Jiechong cycle performance test
The formed battery was charged to 4.4V with a constant current of 0.2C at 45C, and then activated by discharging to 3.0V with a constant current of 0.2C. After activation, the battery is charged to 80% of SOC by using 4C constant current, then is charged to 4.4V by converting 1C constant current and constant voltage, then is discharged to 3.0V by using 1C constant current, and after 1500 times of charge/discharge cycles, the retention rate and the internal resistance increase rate of the 1500 th cycle capacity are calculated. The calculation formula is as follows:
1500 th cycle capacity retention (%) =1500 th cycle discharge capacity/1 st cycle discharge capacity×100%;
the internal resistance increase rate (%) = (the internal resistance after 1500 th cycle-the initial internal resistance before cycle)/the initial internal resistance before cycle×100%.
2. High temperature storage performance
Charging the formed battery to 4.4V at normal temperature with constant current and constant voltage of 0.5C, measuring the initial discharge capacity of the battery, storing for 90 days at 60 ℃, and finally cooling the battery to normal temperature; the holding capacity of the cell was then measured at 1C discharge to 3V. The calculation formula is as follows:
battery capacity retention (%) =retention capacity/initial discharge capacity x 100%.
The test results are shown in Table 2.
TABLE 1
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Note that: 1. LiODFB: lithium difluorooxalato borate;
2、LiBF 4 : lithium tetrafluoroborate;
3. LiBOB: lithium bis (oxalato) borate;
TABLE 2
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As can be seen from the test results of examples 1 to 38 in Table 2, when lithium difluorophosphate and a boron-containing lithium salt are selected as additives, the content B of lithium difluorophosphate, the content C of boron-containing lithium salt, the median particle diameter D of the positive electrode active material and the porosity H of the positive electrode material layer satisfy 0.02.ltoreq.B+C.times.D/H.ltoreq.0.5, and 0.05.ltoreq.B.ltoreq. 1.5,0.05.ltoreq.C.ltoreq.1.5, 2.5.ltoreq.D.ltoreq.6.5, 15.ltoreq.H.ltoreq.40, the contents of lithium difluorophosphate and the boron-containing lithium salt are in dynamic balance with the median particle diameter of the positive electrode active material and the porosity of the positive electrode material layer, the wetting effect and the film forming quality of the electrolyte are ensured, a good positive electrode interface film is formed, the battery quick charge performance and the cycle life are improved, and the high-temperature storage performance is taken into consideration. In examples 1-38, lithium difluorophosphate and boron-containing lithium salt are used in combination to construct an anode interface protective film, so that the migration rate of lithium ions is improved, and the quick charge cycle performance is optimized; meanwhile, the porosity of the positive electrode material layer is controlled, so that the lithium ion transmission difficulty caused by the increase of the viscosity of the electrolyte is reduced; and the relationship between the median particle diameter of the positive electrode active material and the amounts of lithium difluorophosphate and boron-containing lithium salt is controlled, the impedance is reduced, and the cycle life is improved.
From the test results of examples 1 to 16, when the boron-containing lithium salt is only selected from lithium bisoxalato borate, the improvement effect on the high-temperature storage performance of the battery is worse than that of other boron-containing lithium salts, and when the boron-containing lithium salt is selected from lithium difluorooxalato borate and/or lithium tetrafluoroborate or is used in combination with lithium bisoxalato borate and is used in combination with lithium difluorophosphate, the wetting effect and the film forming quality of the electrolyte can be ensured, a good positive electrode interface film is formed, the quick charge performance and the cycle life of the battery are improved, the high-temperature storage performance is also considered, and the battery performance is optimal.
As can be seen from the test results of examples 1 and 17 to 20, the present invention can achieve improvement of the battery fast charge performance and cycle life for different positive electrode active materials when the content B of lithium difluorophosphate, the content C of the boron-containing lithium salt, the median particle diameter D of the positive electrode active material, and the porosity H of the positive electrode material layer satisfy the corresponding conditions.
As can be seen from the test results of examples 21 to 32, when lithium difluorophosphate and a boron-containing lithium salt are used as additives, and vinyl sulfate is used in combination as an additive, the high-temperature storage performance of the battery can be remarkably improved; however, since vinyl sulfate is a sulfur-containing organic compound, the impedance of the battery is increased to some extent. As is clear from comparison of the results of examples 21 to 25, examples 30 to 32 and examples 26 to 29, when the content E of vinyl sulfate satisfies 0.01wt% to 2.5wt% and the content ratio of the boron-containing lithium salt to the vinyl sulfate is between 0.1 and 13, it is possible to realize a positive electrode interface film having an organic component and an inorganic component in a proper ratio, and to improve the high-temperature storage performance of the battery while suppressing the increase in resistance.
From the test results of comparative examples 5 to 16, it was found that even if the value of (b+c) ×d/H was satisfied between 0.02 and 0.5, the lithium ion battery failed to have good quick charge performance and cycle life when any one of the parameters of the content B of lithium difluorophosphate, the content C of the boron-containing lithium salt, the median particle diameter D of the positive electrode active material, and the porosity H of the positive electrode material layer did not satisfy the range limit. From the test results of comparative examples 17 to 18, it was found that even if the content B of lithium difluorophosphate, the content C of the boron-containing lithium salt, the median particle diameter D of the positive electrode active material, and the porosity H of the positive electrode material layer satisfy the range limit, the value of (b+c) ×d/H was too large or too small to achieve both the quick charge performance and the cycle life under the premise of low resistance. It can be seen that the content B of lithium difluorophosphate, the content C of the boron-containing lithium salt, the median particle diameter D of the positive electrode active material, and the porosity H of the positive electrode material layer have strong correlation in improving the battery quick charge performance and cycle life.
As can be seen from the test results of examples 1, 33-35 and the test results of examples 24, 36-38, the addition of tris (trimethylsilane) phosphate (TMSP) in the battery system provided by the invention can further reduce the impedance increase rate; the capacity retention rate of high-temperature storage can be further improved by additionally adding 1, 3-Propane Sultone (PS); the addition of the tripropylester phosphate additive can further improve the capacity retention rate of high-temperature storage and the circulation capacity retention rate, which shows that the lithium difluorophosphate and the boron-containing lithium salt have complementary effects with the vinyl sulfate and other additives.
Compared with the additive (comparative example 1) added with lithium difluorophosphate and the additive (example 1) added with boron-containing lithium salt, the additive (comparative examples 2-4) is not used, the effect of inhibiting the high-temperature cycle life and the impedance growth of the lithium ion battery is poor, and the improvement effect of the cycle capacity retention rate is obviously inferior to that of example 1, which shows that the improvement mechanism of the other additives on the battery performance is different from that of the lithium difluorophosphate and the additive of the boron-containing lithium salt to a certain extent, and the improvement effect of the lithium difluorophosphate and the additive of the boron-containing lithium salt in the system is superior to that of the other additives.
The invention has been further described with reference to specific embodiments, but it should be understood that the detailed description is not to be construed as limiting the spirit and scope of the invention, but rather as providing those skilled in the art with the benefit of this disclosure with the benefit of their various modifications to the described embodiments.

Claims (10)

1. A lithium ion battery is characterized by comprising a positive electrode, a negative electrode and a nonaqueous electrolyte;
the positive electrode includes a positive electrode material layer containing a positive electrode active material including Li 1+ x Ni a Co b M’ 1-a-b O 2-y A y Wherein x is more than or equal to 0.1 and less than or equal to 0.2,0<a<1，0≤b<1，0<a+b<1，0≤y<0.2, m' comprises one or more of Mn, al, sr, mg, ti, ca, zr, zn, si, fe, ce, nb, ga, cu, sn, cr, sr, W or V, a comprises one or more of S, N, F, B, cl, br and I;
the nonaqueous electrolyte comprises a lithium salt, an organic solvent and an additive, wherein the additive comprises lithium difluorophosphate and a boron-containing lithium salt, and the boron-containing lithium salt comprises at least one of lithium difluorooxalato borate, lithium tetrafluoroborate and lithium bisoxalato borate;
the working cut-off voltage of the lithium ion battery is more than or equal to 4.3V;
the lithium ion battery meets the following conditions:
0.02-B+C multiplied by D/H-0.5, B-1.5,0.05-C-1.5, D-6.5, H-40 and B-0.05-1.5,0.05-C-2.5;
wherein B is the mass percentage of lithium difluorophosphate in the nonaqueous electrolyte, and the unit is wt%;
c is the mass percentage of boron-containing lithium salt in the nonaqueous electrolyte, and the unit is wt%;
d is the median particle diameter of the positive electrode active material, and the unit is mu m;
h is the porosity of the positive electrode material layer in%.
2. The lithium ion battery of claim 1, wherein the lithium ion battery meets the following conditions: the (B+C) multiplied by D/H is more than or equal to 0.05 and less than or equal to 0.4.
3. The lithium ion battery according to claim 1, wherein the lithium difluorophosphate accounts for 0.15-1 wt% of the nonaqueous electrolyte.
4. The lithium ion battery according to claim 1, wherein the boron-containing lithium salt accounts for 0.15-1.2 wt% of the nonaqueous electrolyte.
5. The lithium ion battery according to claim 1, wherein the median particle diameter D of the positive electrode active material is 3 μm to 5 μm.
6. The lithium ion battery of claim 1, wherein the positive electrode material layer has a porosity H of 16% to 30%.
7. The lithium ion battery of claim 1, wherein the additive further comprises vinyl sulfate, the lithium ion battery satisfying the following conditions:
0.1≤C/E≤13，0.01≤E≤2.5；
wherein E is the mass percentage of the ethylene sulfate to the nonaqueous electrolyte, and the unit is wt%.
8. The lithium ion battery of claim 7, wherein the lithium ion battery meets the following conditions:
0.5≤C/E≤10，0.03≤E≤1.5。
9. the lithium ion battery of claim 1, wherein the lithium salt comprises LiTFSI, liDFOP, liSbF 6 、LiAsF 6 、LiN(SO 2 C 2 F 5 ) 2 、LiC(SO 2 CF 3 ) 3 、LiClO 4 、LiAlCl 4 、LiCF 3 SO 3 、LiSO 3 F、Li 2 B 10 Cl 10 One or more of lithium chloroborane, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, lithium lower aliphatic carboxylic acid having 4 or less carbon atoms, or lithium tetraphenyl borate.
10. The lithium ion battery according to claim 1, wherein the nonaqueous electrolyte further comprises an auxiliary additive, the auxiliary additive comprising at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, a phosphate compound, a borate compound, and a nitrile compound;
preferably, the content of the auxiliary additive is 0.01-10wt% based on 100% of the total mass of the nonaqueous electrolyte;
preferably, the cyclic sulfate compound is at least one selected from the group consisting of vinyl 4-methyl sulfate and propylene sulfate;
the sultone compound is at least one selected from 1, 3-propane sultone, 1, 4-butane sultone and propenyl-1, 3-sultone;
the cyclic carbonate compound is selected from at least one of ethylene carbonate, methylene ethylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, bifluoroethylene carbonate and a compound shown in the following structural formula 1:
in the structural formula 1, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 Each independently selected from one of a hydrogen atom, a halogen atom, a C1-C5 group;
the phosphate compound is at least one selected from tri (trimethylsilane) phosphate, tri (triethylsilane) phosphate and a compound shown in the following structural formula 2:
in the structural formula 2, R 31 、R 32 、R 33 Each independently selected from the group consisting of C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halogenated hydrocarbon groups, -Si (C) m H 2m+1 ) 3 M is a natural number of 1 to 3, and R 31 、R 32 、R 33 At least one of them is an unsaturated hydrocarbon group;
the borate compound is at least one selected from tri (trimethylsilane) borate and tri (triethylsilane) borate;
the nitrile compound is at least one selected from succinonitrile, glutaronitrile, ethylene glycol bis (propionitrile) ether, hexanedinitrile, adiponitrile, pimelic nitrile, suberonitrile, nonyldinitrile and decyldinitrile.
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Cited By (5)

* Cited by examiner, † Cited by third party
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CN117638201A (en) * 2024-01-24 2024-03-01 宁德新能源科技有限公司 Lithium ion battery and electronic device
CN117638082A (en) * 2024-01-24 2024-03-01 宁德新能源科技有限公司 Lithium ion battery and electronic device
CN117832626A (en) * 2024-03-06 2024-04-05 宁德新能源科技有限公司 Electrolyte, electrochemical device, and electronic apparatus
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Publication number Priority date Publication date Assignee Title
CN117638201A (en) * 2024-01-24 2024-03-01 宁德新能源科技有限公司 Lithium ion battery and electronic device
CN117638082A (en) * 2024-01-24 2024-03-01 宁德新能源科技有限公司 Lithium ion battery and electronic device
CN117638201B (en) * 2024-01-24 2024-04-09 宁德新能源科技有限公司 Lithium ion battery and electronic device
CN117638082B (en) * 2024-01-24 2024-04-09 宁德新能源科技有限公司 Lithium ion battery and electronic device
CN117832626A (en) * 2024-03-06 2024-04-05 宁德新能源科技有限公司 Electrolyte, electrochemical device, and electronic apparatus
CN117855608A (en) * 2024-03-07 2024-04-09 宁德新能源科技有限公司 Electrolyte, secondary battery, and electronic device
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