CN116802875A - Lithium secondary battery - Google Patents
Lithium secondary battery Download PDFInfo
- Publication number
- CN116802875A CN116802875A CN202280011717.9A CN202280011717A CN116802875A CN 116802875 A CN116802875 A CN 116802875A CN 202280011717 A CN202280011717 A CN 202280011717A CN 116802875 A CN116802875 A CN 116802875A
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- CN
- China
- Prior art keywords
- secondary battery
- chemical formula
- lithium
- lithium secondary
- positive electrode
- Prior art date
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- VDVLPSWVDYJFRW-UHFFFAOYSA-N lithium;bis(fluorosulfonyl)azanide Chemical compound [Li+].FS(=O)(=O)[N-]S(F)(=O)=O VDVLPSWVDYJFRW-UHFFFAOYSA-N 0.000 description 1
- QSZMZKBZAYQGRS-UHFFFAOYSA-N lithium;bis(trifluoromethylsulfonyl)azanide Chemical compound [Li+].FC(F)(F)S(=O)(=O)[N-]S(=O)(=O)C(F)(F)F QSZMZKBZAYQGRS-UHFFFAOYSA-N 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
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- 238000002844 melting Methods 0.000 description 1
- 229940017219 methyl propionate Drugs 0.000 description 1
- KKQAVHGECIBFRQ-UHFFFAOYSA-N methyl propyl carbonate Chemical compound CCCOC(=O)OC KKQAVHGECIBFRQ-UHFFFAOYSA-N 0.000 description 1
- PQIOSYKVBBWRRI-UHFFFAOYSA-N methylphosphonyl difluoride Chemical group CP(F)(F)=O PQIOSYKVBBWRRI-UHFFFAOYSA-N 0.000 description 1
- 239000011325 microbead Substances 0.000 description 1
- PYLWMHQQBFSUBP-UHFFFAOYSA-N monofluorobenzene Chemical compound FC1=CC=CC=C1 PYLWMHQQBFSUBP-UHFFFAOYSA-N 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 125000004433 nitrogen atom Chemical group N* 0.000 description 1
- JRZJOMJEPLMPRA-UHFFFAOYSA-N olefin Natural products CCCCCCCC=C JRZJOMJEPLMPRA-UHFFFAOYSA-N 0.000 description 1
- UMLDYULSMQUBPR-UHFFFAOYSA-N oxalic acid;phosphoric acid Chemical compound OP(O)(O)=O.OC(=O)C(O)=O.OC(=O)C(O)=O UMLDYULSMQUBPR-UHFFFAOYSA-N 0.000 description 1
- MHYFEEDKONKGEB-UHFFFAOYSA-N oxathiane 2,2-dioxide Chemical compound O=S1(=O)CCCCO1 MHYFEEDKONKGEB-UHFFFAOYSA-N 0.000 description 1
- 238000002161 passivation Methods 0.000 description 1
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- 229920000139 polyethylene terephthalate Polymers 0.000 description 1
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- 229910052710 silicon Inorganic materials 0.000 description 1
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- UFHILTCGAOPTOV-UHFFFAOYSA-N tetrakis(ethenyl)silane Chemical compound C=C[Si](C=C)(C=C)C=C UFHILTCGAOPTOV-UHFFFAOYSA-N 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
- 239000006163 transport media Substances 0.000 description 1
- CBIQXUBDNNXYJM-UHFFFAOYSA-N tris(2,2,2-trifluoroethyl) phosphite Chemical compound FC(F)(F)COP(OCC(F)(F)F)OCC(F)(F)F CBIQXUBDNNXYJM-UHFFFAOYSA-N 0.000 description 1
- VMZOBROUFBEGAR-UHFFFAOYSA-N tris(trimethylsilyl) phosphite Chemical compound C[Si](C)(C)OP(O[Si](C)(C)C)O[Si](C)(C)C VMZOBROUFBEGAR-UHFFFAOYSA-N 0.000 description 1
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Abstract
The present application relates to a lithium secondary battery in which an abnormal voltage drop phenomenon is improved. The lithium secondary battery includes: a negative electrode including a negative electrode active material, a positive electrode including a positive electrode active material represented by chemical formula 1, a separator provided between the positive electrode and the negative electrode, and a nonaqueous electrolyte solution, wherein the nonaqueous electrolyte solution includes a lithium salt; a non-aqueous organic solvent; a compound represented by chemical formula 2 as a first additive; and lithium difluorophosphate as a second additive.
Description
Technical Field
Cross Reference to Related Applications
The present application claims priority from korean patent application No. 10-2021-01333482 filed on 7 th 10 th 2021 and korean patent application No. 10-2022-012587 filed on 9 th 2022, the disclosures of which are incorporated herein by reference.
The present application relates to a lithium secondary battery having improved battery durability.
Background
As the dependence of modern society on electric energy increases, research into renewable energy sources capable of increasing electric energy production without causing environmental problems has emerged.
Since renewable energy sources exhibit intermittent power generation characteristics, large-capacity energy storage devices are critical for stable power supply. Among these energy storage devices, lithium ion batteries have been commercialized as devices having high energy density, and thus have received attention.
Lithium ion batteries generally comprise: a positive electrode containing a positive electrode active material containing a lithium-containing transition metal oxide, a negative electrode containing a negative electrode active material capable of storing lithium ions, an electrolyte solution as a lithium ion transport medium, and a separator.
The positive electrode stores energy through the oxidation-reduction reaction of the transition metal, and results in the fact that the transition metal must be contained in the positive electrode material.
The electrolyte solution of the lithium ion battery consists of a lithium salt, an organic solvent that dissolves the lithium salt, and a functional additive, wherein the proper selection of these components is very important for improving the electrochemical properties of the battery.
Because of the lithium salt contained in the nonaqueous electrolyte solution (in generalIs LiPF 6 Etc.) are susceptible to heat or moisture, so they react with or thermally decompose with moisture present in the cell to form lewis acids, e.g., HF or PF 5 . These lewis acids corrode and degrade the passivation film generated at the electrode-electrolyte interface, thereby causing elution of transition metal ions from the positive electrode due to side reactions between the exposed positive electrode surface and the electrolyte solution.
In particular, when a high Ni positive electrode active material having a Ni content higher than 0.5 is used, dissolution of transition metal from the positive electrode and disintegration of the positive electrode structure more easily occur because the crystal structure of the positive electrode is deformed and disintegrated during repeated charge and discharge or when exposed to high temperature. And the dissolved transition metal is electrodeposited on the surface of the anode after being transferred to the anode through the electrolyte solution, resulting in destruction and regeneration reaction of the Solid Electrolyte Interphase (SEI) film, and thus, additional lithium ion consumption. This causes the phenomena of an increase in resistance, a decrease in capacity, and an abnormal voltage drop of the battery, and further accelerates the decomposition of the electrolyte solvent to accelerate gas generation. Therefore, there is a problem in that the stability and high temperature durability of the secondary battery are deteriorated.
Accordingly, in order to improve the problem, research has been conducted to develop a lithium secondary battery using a lithium secondary battery capable of removing by-products (HF, PF) generated by thermal decomposition of lithium salts 5 Etc.) and forms a stable film on the electrode surface, and a positive electrode containing a positive electrode active material having a specific composition.
Disclosure of Invention
[ technical problem ]
An aspect of the present invention provides a lithium secondary battery having improved high temperature stability, high temperature cycle characteristics, and abnormal voltage drop by using a positive electrode including a positive electrode active material of a specific composition and a non-aqueous electrolyte solution including two additives capable of forming a stable ion conductive film on the surface of an electrode.
Technical scheme
According to one embodiment, the present invention provides a lithium secondary battery, comprising: a negative electrode including a negative electrode active material, a positive electrode including a positive electrode active material represented by the following chemical formula 1, a separator provided between the negative electrode and the positive electrode, and a nonaqueous electrolyte solution, wherein the nonaqueous electrolyte solution includes: a lithium salt; a non-aqueous organic solvent; a compound represented by the following chemical formula 2 as a first additive; lithium difluorophosphate as a second additive:
[ chemical formula 1]
Li a Ni x Co y M 1 z M 2 w O 2
In the chemical formula 1, the chemical formula is shown in the drawing,
M 1 is Mn, al or a combination thereof,
M 2 is at least one selected from the group consisting of Al, zr, W, ti, M, ca and Sr, wherein a is 0.8.ltoreq.a.ltoreq.1.2, and x is 0.7.ltoreq.x<1、0<y<0.3、0<z<0.3、0.01<w≤0.2；
[ chemical formula 2]
In chemical formula 2, R is an alkylene group having 1 to 5 carbon atoms.
The weight ratio of the compound represented by the above chemical formula 2 to lithium difluorophosphate may be 1:2 to 1:15.
[ advantageous effects ]
The lithium secondary battery of the present invention uses a positive electrode comprising a positive electrode active material of a specific composition and a nonaqueous electrolyte solution comprising a specific additive (for example, an imidazole compound and lithium difluorophosphate, the vinyl groups of which are substituted in the structure) so as to be able to form an electrochemically stable ion-conducting film on the surface of the positive electrode while effectively scavenging lewis acid (PF) generated as a decomposition product of the electrolyte 5 ) This makes it possible to realize a lithium secondary battery which improves high-temperature stability, high-temperature cycle characteristics, and abnormal voltage drop phenomenon.
Detailed Description
Hereinafter, the present invention will be described in more detail.
It should be understood that words or terms used in the specification and claims of the present invention should not be construed as meanings defined in commonly used dictionaries, and it should be further understood that these words or terms should be interpreted as meanings consistent with their meanings in the technical ideas of the present invention in the context of the relevant technical fields, based on the principle that the inventors can properly define the meanings of the words or terms to best explain the invention.
Meanwhile, the terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to be limiting of the invention. The singular is also intended to include the plural unless the context clearly indicates otherwise. It will be further understood that terms such as "comprises," "comprising," "includes," or "having," and the like, when used herein, are intended to specify the presence of stated features, integers, steps, elements, and/or groups thereof, but do not preclude the presence or addition of other specified features, integers, steps, elements, and/or groups thereof.
Before describing the present invention, the expressions "a" and "b" in the description of "a to b carbon atoms" respectively represent the number of carbon atoms contained in a specific functional group. That is, the functional group may contain "a" to "b" carbon atoms. For example, "alkyl having 1 to 5 carbon atoms" means an alkyl group having 1 to 5 carbon atoms, i.e., -CH 3 、-CH 2 CH 3 、-CH 2 CH 2 CH 3 、-CH 2 (CH 3 )CH 3 、-CH(CH 3 )CH 3 and-CH (CH) 3 )CH 2 CH 3 Etc.
In addition, unless otherwise defined in the specification, the expression "substituted" means that at least one hydrogen atom bonded to a carbon atom is replaced with an element other than hydrogen, for example, an alkyl group having 1 to 5 carbon atoms or a fluorine element.
In the specification, unless explicitly stated otherwise, the expression "%" means% by weight.
In general, the amount of lithium ions available in a battery decreases due to a change in the structure of the positive electrode caused by the generation of Hydrogen Fluoride (HF) from an electrolyte solution or repeated charge and discharge during the operation of the battery, while transition metals are easily eluted from the positive electrode into the electrolyte solution, and thus the battery capacity may decrease. In addition, the eluted transition metal ions are redeposited on the positive electrode, increasing the resistance of the positive electrode. In addition, the transition metal migrates to the anode through the electrolyte solution to destroy a Solid Electrolyte Interface (SEI) or electrodeposit on the anode surface, resulting in internal short circuit of the battery while growing dendrites. This series of reactions promotes the electrolyte solution decomposition reaction, thereby increasing the interfacial resistance of the anode, and causing additional low voltage failure due to self-discharge of the anode.
The present invention provides a lithium secondary battery comprising a nonaqueous electrolyte solution for a lithium secondary battery, the nonaqueous electrolyte solution comprising two additives capable of suppressing additional elution of transition metals by forming firm films on the surfaces of a positive electrode and a negative electrode, and preventing electrodeposition on the negative electrode by scavenging transition metal ions that are the cause of deterioration and operational failure.
Lithium secondary battery
According to one embodiment, the present invention provides a lithium secondary battery, comprising: a negative electrode containing a negative electrode active material, a positive electrode containing a positive electrode active material represented by the following chemical formula 1, a separator provided between the negative electrode and the positive electrode, and a nonaqueous electrolyte solution,
wherein the non-aqueous electrolyte solution comprises: a lithium salt; a non-aqueous organic solvent; a compound represented by the following chemical formula 2 as a first additive; lithium difluorophosphate as a second additive:
[ chemical formula 1]
Li a Ni x Co y M 1 z M 2 w O 2
In the chemical formula 1, the chemical formula is shown in the drawing,
M 1 is Mn, al or a combination thereof,
M 2 is at least one selected from the group consisting of Al, zr, W, ti, M, ca and Sr, wherein a is 0.8.ltoreq.a.ltoreq. 1.2,0.7.ltoreq.x<1，0<y<0.3，0<z<0.3，0.01<w≤0.2；
[ chemical formula 2]
In chemical formula 2, R is an alkylene group having 1 to 5 carbon atoms.
The lithium secondary battery of the present invention may be prepared as follows: an electrode assembly in which a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode are sequentially stacked is formed, the electrode assembly is contained in a battery case, and then the non-aqueous electrolyte solution of the present invention is injected. The lithium secondary battery of the present invention may be prepared according to a conventional method known and used in the art, and the preparation method of the lithium secondary battery of the present invention is specifically described as follows.
Hereinafter, each component constituting the lithium secondary battery of the present invention will be described in more detail.
(1) Negative electrode
Next, the negative electrode of the present invention will be described.
The anode of the present invention may contain an anode active material layer containing an anode active material, and the anode active material layer may further contain a conductive agent and/or a binder, if necessary.
As the anode active material, various anode active materials used in the art, for example, carbon-based anode active materials, silicon-based anode active materials, or a mixture thereof may be used.
According to an embodiment, the anode active material may include a carbon-based anode active material, and as the carbon-based anode active material, various carbon-based anode active materials used in the art, for example, graphite-based materials such as natural graphite, artificial graphite, and Kish graphite; high temperature sintered carbon such as pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microbeads, mesophase pitch, petroleum or coal tar pitch-derived cokes; soft carbon and hard carbon. The shape of the carbon-based anode active material is not particularly limited, and materials of various shapes, such as irregular, planar, flake-like, spherical, or fibrous, may be used.
Preferably, the anode active material may include at least one carbon-based anode active material selected from natural graphite and artificial graphite, and the natural graphite and artificial graphite may be used together to increase adhesion with a current collector and to suppress exfoliation of the active material.
According to another embodiment, the anode active material may include a silicon-based anode active material and a carbon-based anode active material together.
The silicon-based anode active material may be selected from, for example, si, siO x (wherein 0<x<2) SiC and Si-Y alloys (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si). The element Y may be selected from the group consisting of M, ca, sr, ba, ra, sc, Y, ti, zr, hf, rf, V, nb, ta,Cr, mo, W, tc, re, bh, fe, pb, ru, os, hs, rh, ir, pd, pt, cu, au, zn, cd, B, al, ga, sn, in, ti, ge, P, as, sb, bi, S, se, te, po and combinations thereof.
Since the silicon-based anode active material has higher capacity characteristics than the carbon-based anode active material, better capacity characteristics can be obtained when the silicon-based anode active material is further contained. However, silicon-containing cathodes contain more O-rich components in the SEI film than graphite cathodes, and lewis acids (e.g., HF or PF are present in the electrolyte solution 5 ) When an SEI film containing an O-rich component tends to be decomposed more easily. Therefore, for a negative electrode containing a silicon-based negative electrode active material, in order to maintain a stable SEI film, it is necessary to suppress lewis acid (e.g., HF or PF in an electrolyte solution 5 ) And (c) forming or removing (or scavenging) the lewis acid that has formed. Because the nonaqueous electrolyte solution of the present invention forms stable films on the positive electrode and the negative electrode and contains the electrolyte additive having excellent effect of removing Lewis acidSo that decomposition of the SEI film can be effectively suppressed when a negative electrode containing a silicon-based negative electrode active material is used.
The mixing weight ratio of the silicon-based anode active material to the carbon-based anode active material may be 3:97 to 99:1, preferably 5:95 to 15:85. In the case where the mixing ratio of the silicon-based anode active material to the carbon-based anode active material satisfies the above range, excellent cycle performance can be ensured because the volume expansion of the silicon-based anode active material is suppressed while improving the capacity characteristics.
The content of the anode active material may be 80 to 99 wt% based on the total weight of the anode active material layer. When the amount of the anode active material satisfies the above range, excellent capacity characteristics and electrochemical characteristics can be obtained.
In addition, the conductive agent is a component that further improves the conductivity of the anode active material, wherein the conductive agent may be added in an amount of 1 to 20 wt% based on the total weight of the anode active material layer. Any conductive agent may be used without particular limitation as long as it has conductivity and does not cause adverse chemical changes in the battery, for example, the following conductive materials may be used: graphite, such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers, such as carbon fibers or metal fibers; conductive powders such as fluorocarbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or a polyphenylene derivative.
The binder is a component assisting in adhesion between the conductive agent, the active material, and the current collector, wherein the binder is generally added in an amount of 1 to 30% by weight based on the total weight of the anode active material layer. Examples of the binder may be a fluororesin-based binder including polyvinylidene fluoride (PVDF) or Polytetrafluoroethylene (PTFE); rubber-based adhesives including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulosic binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; a polyol-based binder including polyvinyl alcohol; polyolefin adhesives, including polyethylene or polypropylene; polyimide-based adhesives; a polyester-based adhesive; a silane-based adhesive.
The anode may be prepared by an anode preparation method known in the art. For example, the anode may be prepared by the following method: preparing a negative electrode active material slurry by dissolving or dispersing a negative electrode active material and optionally a binder and a conductive agent in a solvent on a negative electrode current collector, coating the negative electrode current collector with the negative electrode active material slurry, rolling and drying; or casting the anode active material slurry on a separate support and then laminating a membrane separated from the support on the anode current collector.
The negative electrode current collector may generally have a thickness of 3 μm to 500 μm. The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause adverse chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. Like the positive electrode current collector, microscopic irregularities may be formed on the surface of the current collector to improve adhesion of the negative electrode active material. For example, various shapes of negative electrode current collectors, such as films, sheets, foils, nets, porous bodies, foam bodies, non-woven fabrics, and the like, may be used.
The solvent may include water or an organic solvent such as NMP and alcohol, and may be used in such an amount that a desired viscosity is obtained when the anode active material, and optionally, a binder and a conductive agent are contained. For example, the content of the solvent may be such that the solid content in the active material slurry containing the anode active material and optionally the binder and the conductive agent is 50 to 75 wt%, preferably 40 to 70 wt%.
(2) Positive electrode
Next, the positive electrode will be described.
The positive electrode of the present invention may include a positive electrode active material layer containing a positive electrode active material, and, if necessary, the positive electrode active material layer may further include a conductive agent and/or a binder.
The positive electrode active material layer may include lithium-nickel-cobalt-manganese-transition metal (M) oxide represented by the following chemical formula 1.
[ chemical formula 1]
Li a Ni x Co y M 1 z M 2 w O 2
In the chemical formula 1, the chemical formula is shown in the drawing,
M 1 is Mn, al or a combination thereof, and may be preferably Mn, or Mn and Al.
M 2 Is at least one selected from Al, zr, W, ti, M, ca and Sr, and may preferably be at least one selected from Al, zr, Y, M and Ti, and may more preferably be Al.
a represents the molar ratio of lithium in the lithium nickel-based oxide and may be 0.8.ltoreq.a.ltoreq.1.2, specifically 0.85.ltoreq.a.ltoreq.1.15, and more specifically 0.9.ltoreq.a.ltoreq.1.05. When the molar ratio of lithium satisfies the above range, the crystal structure of lithium nickel-based oxide can be stably formed.
x represents the molar ratio of nickel in all metals except lithium in the lithium nickel-based oxide and may be 0.7.ltoreq.x <1, specifically 0.75.ltoreq.x.ltoreq.0.99, more specifically 0.8.ltoreq.x.ltoreq.0.95, and more specifically 0.85.ltoreq.x.ltoreq.0.95. When the molar ratio of nickel satisfies the above range, it is possible to exhibit high energy density and achieve high capacity.
y represents the molar ratio of cobalt in all metals except lithium in the lithium nickel-based oxide and may be 0< y <0.3, preferably 0.001< y <0.3, particularly 0.01< y <0.25, more particularly 0.01.ltoreq.y <0.20, and more particularly 0.01.ltoreq.y <0.15. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be achieved.
z represents M in all metals except lithium in lithium nickel-based oxide 1 And may be 0.001<z<0.25, preferably 0.01.ltoreq.z<0.20, more preferably 0.01.ltoreq.z<0.20, and more specifically 0.01.ltoreq.z<0.15. When M 1 When the molar ratio satisfies the above range, the structural stability of the positive electrode active material is excellent.
w represents M in all metals except lithium in lithium nickel-based oxide 2 And may be 0.01<w is less than or equal to 0.2, specifically 0.01<w.ltoreq.0.1, and preferably 0.01<w≤0.05。
Specifically, in order to realize a high-capacity battery, the single-particle-based positive electrode active material may include Li (Ni 0.8 Co 0.15 Al 0.05 )O 2 、Li(Ni 0.85 Mn 0.08 Co 0.05 Al 0.02 )O 2 、Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O 2 、Li(Ni 0.87 Mn 0.07 Co 0.04 Al 0.02 )O 2 Or Li (Ni) 0.90 Mn 0.03 Co 0.05 Al 0.02 )O 2 。
In the case of using a high Ni lithium transition metal oxide having Ni content of more than 0.7 as a positive electrode active material, since Li + Ion and Ni 2+ The sizes of the ions are close to each other, so Li occurs in the layered material of the positive electrode active material during charge and discharge + Ion and Ni 2+ The positions of the ions change the cation mixing and discharging phenomenon with each other. That is, according to the change in the oxidation number of Ni contained in the positive electrode active material, the nickel transition metal having d-orbitals necessarily has an octahedral structure when forming coordination bonds in an environment such as a high temperature, but the crystal structure of the positive electrode active material may be deformed and disintegrated due to heterogeneous reactions of energy level order reversal or oxidation number change caused by external energy supply, while forming a distorted octahedral structure. In addition, since another side reaction occurs in which transition metal, particularly nickel metal, is eluted from the positive electrode active material due to side reaction between the positive electrode active material and the electrolyte solution during high temperature storage, the overall performance of the secondary battery is deteriorated due to structural disintegration of the positive electrode active material and exhaustion of the electrolyte solution.
The present invention can solve this problem by using a positive electrode containing a high content of nickel transition metal oxide and a nonaqueous electrolyte solution containing a specific additive. That is, a strong ion-conductive film is formed on the surface of the positive electrode to suppress Li using a nonaqueous electrolyte solution containing an additive having a specific composition + Ions andNi 2+ the cation mixing and discharging phenomenon of the ions and effectively inhibits side reactions between the positive electrode and the electrolyte solution and occurrence of metal dissolution, thus alleviating structural instability of the high-capacity electrode. Accordingly, since a sufficient amount of nickel transition metal for securing the capacity of the lithium secondary battery can be secured, the energy density can be increased to prevent the reduction of the output characteristics.
The content of the positive electrode active material may be 80 to 99 wt%, specifically, 90 to 99 wt%, based on the total weight of the positive electrode active material layer. Here, when the amount of the positive electrode active material is 80% or less, the energy density is reduced, and thus the capacity is reduced.
The conductive agent may be used without particular limitation as long as it has conductivity without causing adverse chemical changes in the battery, for example, carbon powder such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder, such as natural graphite, artificial graphite, or graphite having a highly developed crystal structure; conductive fibers, such as carbon fibers or metal fibers; conductive powders such as fluorocarbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or a polyphenylene derivative. The conductive agent may be added in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.
The binder is a component that aids in the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector, wherein the binder is generally added in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer. Examples of the binder may be a fluororesin-based binder including polyvinylidene fluoride (PVDF) or Polytetrafluoroethylene (PTFE); rubber-based adhesives including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulosic binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; a polyol-based binder including polyvinyl alcohol; polyolefin adhesives, including polyethylene or polypropylene; polyimide-based adhesives; a polyester-based adhesive; a silane-based adhesive.
The positive electrode may be prepared by a positive electrode preparation method well known in the art. For example, the positive electrode may be prepared by: dissolving or dispersing a positive electrode active material, a binder and/or a conductive agent in a solvent to prepare a positive electrode slurry, coating a positive electrode current collector with the positive electrode slurry, and then rolling and drying; or casting the positive electrode active material layer on a separate support and then laminating a membrane separated from the support on the positive electrode current collector.
The positive electrode current collector is not particularly limited as long as it has conductivity without causing adverse chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon, aluminum surface-treated with carbon, nickel, titanium, silver, or the like, or stainless steel may be used.
The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount such that a desired viscosity is obtained when the positive electrode active material, and optionally, the binder and the conductive agent are contained. For example, the content of the solvent may be such that the solid content in the active material slurry including the positive electrode active material and optional binder and conductive agent is 10 to 90 wt%, preferably 30 to 80 wt%.
(3) Diaphragm
As the separator included in the lithium secondary battery of the present invention, a general porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer and ethylene/methacrylate copolymer, may be used alone or in a laminated form, or a general porous non-woven fabric, for example, a non-woven fabric formed of high-melting glass fiber or polyethylene terephthalate fiber, may be used, but the present invention is not limited thereto.
(4) Nonaqueous electrolyte solution
Next, the nonaqueous electrolyte solution of the present invention will be described.
The non-aqueous electrolyte solution of the present invention may comprise: a lithium salt; a non-aqueous organic solvent; a compound represented by chemical formula 2 as a first additive; and lithium difluorophosphate as a second additive, and optionally may further comprise a third additive.
(4-1) lithium salt
First, a lithium salt will be described.
As the lithium salt, any lithium salt commonly used in nonaqueous electrolyte solutions for lithium secondary batteries may be used without limitation, and for example, the lithium salt may contain Li + As cations, and may contain a cation selected from the group consisting of F - 、Cl - 、Br - 、I - 、NO 3 - 、N(CN) 2 - 、BF 4 - 、ClO 4 - 、B 10 Cl 10 - 、AlCl 4 - 、AlO 4 - 、PF 6 - 、SO 3 F - 、CF 3 SO 3 - 、CH 3 CO 2 - 、CF 3 CO 2 - 、AsF 6 - 、SbF 6 - 、CH 3 SO 3 - 、(CF 3 CF 2 SO 2 ) 2 N - 、(CF 3 SO 2 ) 2 N - 、(FSO 2 ) 2 N - 、(PO 2 F 2 ) - 、(FSO 2 )(POF 2 )N - 、BF 2 C 2 O 4 - 、BC 4 O 8 - 、PF 4 C 2 O 4 - 、PF 2 C 4 O 8 - 、(CF 3 ) 2 PF 4 - 、(CF 3 ) 3 PF 3 - 、(CF 3 ) 4 PF 2 - 、(CF 3 ) 5 PF - 、(CF 3 ) 6 P - 、C 4 F 9 SO 3 - 、CF 3 CF 2 SO 3 - 、CF 3 CF 2 (CF 3 ) 2 CO - 、(CF 3 SO 2 ) 2 CH - 、CF 3 (CF 2 ) 7 SO 3 - And SCN - At least one of the group consisting of as an anion.
In particular, the lithium salt may comprise a compound selected from the group consisting of LiCl, liBr, liI, liBF 4 、LiClO 4 、LiB 10 Cl 10 、LiAlCl 4 、LiAlO 4 、LiPF 6 、LiSO 3 F、LiCF 3 SO 3 、LiCH 3 CO 2 、LiCF 3 CO 2 、LiAsF 6 、LiSbF 6 、LiCH 3 SO 3 、LiN(SO 2 F) 2 Lithium bis (fluorosulfonyl) imide, liLSI, liN (SO) 2 CF 2 CF 3 ) 2 Lithium bis (pentafluoroethylsulfonyl) imide, liBETI, and LiN (SO) 2 CF 3 ) 2 A single material of the group consisting of lithium bis (trifluoromethanesulfonyl) imide, liTFSI, or a mixture of two or more thereof. In addition to these materials, a lithium salt commonly used in an electrolyte solution of a lithium secondary battery may be used without limitation. In particular, the lithium salt may comprise LiPF 6 。
The lithium salt may be appropriately changed within a generally usable range, but the concentration of the lithium salt contained in the electrolyte solution may be 0.8M to 3.0M, specifically 1.0M to 3.0M, to obtain an optimal effect of forming an anti-corrosion film on the electrode surface. In the case where the concentration of the lithium salt is within the above concentration range, the viscosity of the nonaqueous electrolyte solution can be controlled to achieve optimal impregnability, and the effect of improving the capacity and cycle characteristics of the lithium secondary battery can be obtained by improving the mobility of lithium ions.
(4-2) non-aqueous organic solvent
In addition, a nonaqueous organic solvent will be described.
As the nonaqueous organic solvent, various nonaqueous organic solvents commonly used in nonaqueous electrolyte solutions can be used without limitation. The nonaqueous organic solvent is not limited as long as decomposition caused by oxidation reactions during charge and discharge of the secondary battery can be minimized and desired characteristics can be exhibited in the presence of the additive.
In particular, the non-aqueous organic solvent having higher ionic conductivity may include a cyclic carbonate compound of high viscosity (which well dissociates lithium salt due to high dielectric constant) and a linear carbonate compound of low viscosity and low dielectric constant.
The cyclic carbonate compound may include at least one selected from the group consisting of Ethylene Carbonate (EC), propylene Carbonate (PC), 1, 2-butylene carbonate, 2, 3-butylene carbonate, 1, 2-pentylene carbonate, 2, 3-pentylene carbonate, and vinylene carbonate, wherein ethylene carbonate may be included.
The linear carbonate compound may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate, and in particular may include ethylmethyl carbonate (EMC).
In the present invention, a mixture of a cyclic carbonate compound and a linear carbonate compound may be used, wherein a mixing ratio of the cyclic carbonate compound to the linear carbonate compound may be in a range of 10:90 to 80:20 by volume, and particularly may be 30:70 to 50:50 by volume. In the case where the mixing ratio of the cyclic carbonate compound to the linear carbonate compound satisfies the above range, a nonaqueous electrolyte solution having higher conductivity can be prepared.
In addition, in order to improve the disadvantages of the carbonate compound and increase the stability during high-temperature and high-voltage driving, a propionate compound may be further mixed as a non-aqueous organic solvent.
The propionate compound may include at least one selected from the group consisting of methyl propionate, ethyl Propionate (EP), propyl propionate, and butyl propionate. Specifically, at least one of ethyl propionate and propyl propionate may be included.
In the nonaqueous electrolyte solution, unless otherwise specified, the remainder other than the nonaqueous organic solvent (e.g., lithium salt, oligomer, and optionally additives) may be the nonaqueous organic solvent.
(4-3) first additive
The nonaqueous electrolyte solution for a lithium secondary battery of the present invention may contain a compound represented by the following chemical formula 2 as a first additive.
(chemical formula 2)
In chemical formula 2, R is an alkylene group having 1 to 5 carbon atoms.
R may further comprise at least one unsaturated bond.
The compound represented by chemical formula 2 contains an imidazole structure capable of acting as a lewis base. Thus, the nitrogen atom of the imidazolyl group can effectively scavenge lewis acid generated as a lithium salt decomposition product. During charge and discharge, when the battery reaches a predetermined voltage, vinyl groups in the structure of the compound represented by chemical formula 2 are reduced on the surface of the anode, thereby forming an ion conductive film on the surface of the anode. The ion-conductive film can inhibit the decomposition reaction of the additional electrolyte solution. This can also improve cycle life characteristics and high temperature storage performance by promoting intercalation and deintercalation of lithium ions in the anode during repeated charge and discharge or during high temperature storage, and can improve resistivity increase by effectively preventing electrodeposition of lithium ions caused by eluted transition metal or overvoltage
Specifically, in chemical formula 2, R may be an alkylene group having 1 to 3 carbon atoms. More specifically, the compound represented by chemical formula 2 may be a compound represented by chemical formula 2a below.
[ chemical formula 2a ]
The content of the compound represented by chemical formula 2 may be 0.1 to 5.0 wt% based on the total weight of the nonaqueous electrolyte solution.
In the case where the content of the compound represented by chemical formula 2 is within the above range, a secondary battery with further improved overall performance can be manufactured. For example, when the amount of the first additive is 0.1 wt% or more, a stabilization effect and a dissolution-inhibiting effect can be obtained during formation of the SEI film, while suppressing an increase in resistance, so that an effect of improving abnormal voltage drop can be obtained. In addition, when the amount of the additive is 5.0 wt% or less, an increase in viscosity of the electrolyte solution caused by the excessive compound can be prevented, and an increase in battery resistance can be effectively prevented by suppressing excessive formation of a film. Therefore, the maximum dissolution-inhibiting effect can be obtained within the allowable resistance increase range.
Specifically, when the content of the compound represented by chemical formula 2 is 0.3 to 3.0 wt%, specifically 0.3 to 2.5 wt%, based on the total weight of the nonaqueous electrolyte solution, a secondary battery with further improved overall performance can be manufactured.
(4-4) second additive
In addition, by mixing a lithium salt additive such as lithium difluorophosphate (LiDFP) as a second additive, the non-aqueous electrolyte solution of the present invention can form a film containing an inorganic component and having improved thermal stability on the surface of the positive electrode.
Lithium difluorophosphate is a component for achieving an effect of improving long-term life characteristics of a secondary battery, in which, since lithium difluorophosphate is electrochemically decomposed on the surfaces of a positive electrode and a negative electrode to assist in forming an ion conductive film, it can suppress elution of metal from the positive electrode and can prevent side reactions between the electrode and an electrolyte solution, thereby achieving an effect of improving high-temperature storage characteristics and cycle life characteristics of a secondary battery.
In the non-aqueous electrolyte solution of the present invention, the weight ratio of the compound represented by chemical formula 2 as the first additive to lithium difluorophosphate as the second additive may be 1:2 to 1:15. When the content of the compound represented by chemical formula 2 and lithium difluorophosphate is in the above range, the effect of removing the decomposition product generated from the lithium salt can be further improved, and at the same time, a film excellent in thermal stability is formed on the electrode surface, whereby the output of the secondary battery can be improved.
Specifically, the compound represented by chemical formula 2 and lithium difluorophosphate may be contained in a weight ratio of 1:2 to 1:10, more specifically 1:2 to 1:7.
In the case where the compound represented by chemical formula 2 and lithium difluorophosphate are contained in equal amounts (e.g., 1:1), the highly ion conductive component generated by decomposition of lithium difluorophosphate is relatively reduced, while the organic film derived from the compound represented by chemical formula 2 is formed relatively thicker, the initial film resistance may increase and the overpotential may be exacerbated. Therefore, when used with a positive electrode active material using a lithium transition metal oxide having a high nickel (Ni) content of Ni content of more than 0.7, decomposition of an electrolyte solution and an aging rate of the active material may be accelerated, and thus long-term durability (cycle characteristics, etc.) may be relatively deteriorated.
(4-5) third additive
In addition, in order to prevent the decomposition of the nonaqueous electrolyte solution under a high output environment from causing the disintegration of the positive electrode, or to further improve the low-temperature high-rate discharge characteristic, the high-temperature stability, the overcharge protection, and the battery expansion suppressing effect at high temperature, the nonaqueous electrolyte solution for a lithium secondary battery of the present invention may further contain another additional third additive, if necessary, in addition to the above two additives.
Examples of the third additive may be at least one selected from the group consisting of cyclic carbonate compounds, halogenated carbonate compounds, sultone compounds, sulfate/salt compounds, phosphate/salt or phosphite/salt compounds, borate/ester compounds, benzene compounds, amine compounds, imidazole compounds, silane compounds, and lithium salt compounds.
The cyclic carbonate compound may include Vinylene Carbonate (VC) or Vinyl Ethylene Carbonate (VEC).
The halogenated carbonate compound may include fluoroethylene carbonate (FEC) and the like.
As a specific example, the sultone-based compound may include at least one selected from the group consisting of 1, 3-Propane Sultone (PS), 1, 4-butane sultone, ethane sultone, 1, 3-propylene sultone (PRS), 1, 4-butene sultone, and 1-methyl-1, 3-propylene sultone.
As a specific example, the sulfate/salt compound may be ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyltrimethylene sulfate (MTMS).
The phosphate or phosphite/salt compound may be, for example, at least one selected from the group consisting of lithium difluoro (bisoxalic acid) phosphate, lithium difluoro phosphate, tris (trimethylsilyl) phosphite, tris (2, 2-trifluoroethyl) phosphate, and tris (trifluoroethyl) phosphite.
The borate/ester compound may include, for example, tetraphenyl borate capable of forming a film on the surface of the anode, lithium oxalyldifluoroborate (LiODFB) or lithium bis (oxalato) borate (LiB (C) 2 O 4 ) 2 ，LiBOB)。
The benzene compound can be fluorobenzene, and the amine compound can be triethanolamine or ethylenediamine.
The imidazole compound can be 2-trifluoromethyl-4, 5-dicyanoimidazole lithium, 1-methyl-5-propargyl imidazole, propargyl 1H-imidazole-1-formic acid, 1-vinyl imidazole or allyl 1H-imidazole-1-formic acid.
The silane compound may be tetravinyl silane.
The lithium salt compound is a compound different from the lithium salt contained in the non-aqueous electrolyte solution, wherein the lithium salt compound may include LiPO 2 F 2 、LiSO 3 F or LiBF 4 。
Among these third additives, in order to form a stronger SEI film on the anode surface during initial activation, other additives having an excellent effect of forming a film on the anode surface may be included, specifically selected from the group consisting of vinylene carbonate, 1, 3-propane sultone, ethylene sulfate, fluoroethylene carbonate (FEC), liBF 4 And lithium difluorophosphate (LiPO) 2 F 2 ) At least one of the group consisting of.
The third additive may be used by mixing two or more compounds, and the content of the third additive may be 0.01 to 50% by weight, particularly 0.01 to 20% by weight, preferably 0.05 to 15% by weight, based on the total weight of the nonaqueous electrolyte solution. The amount of the above other additives is desirable in the above range because the high-temperature storage characteristics and cycle life characteristics can be improved, side reactions due to the addition of excessive additives can be prevented, and unreacted materials can be prevented from precipitating or remaining.
The shape of the lithium secondary battery of the present invention is not particularly limited, and may be cylindrical, prismatic, pouch-shaped, or coin-shaped using a can.
Hereinafter, the present invention will be described in more detail according to examples. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these example embodiments are provided so that this description will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
Examples
Example 1
(preparation of nonaqueous electrolyte solution)
LiPF is put into 6 Dissolving in non-aqueous organic solvent (ethylene carbonate (EC) and methyl ethylene carbonate (EMC) mixed at a volume ratio of 30:70) to give LiPF 6 After that, 0.1% by weight of the compound represented by chemical formula 2a, 1.0% by weight of lithium difluorophosphate, and as a third additive, 0.5% by weight of Vinylene Carbonate (VC), 0.5% by weight of 1, 3-Propane Sultone (PS) and 1.0% by weight of ethylene sulfate (ESa) were added, thereby preparing a nonaqueous electrolyte solution (see table 1 below).
(preparation of secondary battery)
The positive electrode active material (Li (Ni 0.85 Mn 0.08 Co 0.05 Al 0.02 )O 2 ) The conductive agent (carbon black) and the binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 97.6:0.8:1.6 to prepare a positive electrode active material slurry (solid content 72 wt%). A positive electrode current collector (Al thin film) 13.5 μm thick was coated with a positive electrode active material slurry, dried and rolled to prepare a positive electrode.
The anode active material (weight ratio of artificial graphite to natural graphite=80:20), binder (SBR-CMC), and conductive agent (carbon black) were added to water as a solvent in a weight ratio of 95.6:3.4:1.0 to prepare an anode active material slurry (solid content: 50 wt%). A negative electrode current collector (Cu thin film) of 6 μm thickness was coated with a negative electrode active material slurry, dried and rolled to prepare a negative electrode.
The positive electrode and the inorganic particles (Al 2 O 3 ) An electrode assembly was prepared from the polyolefin-based porous separator and the negative electrode, and then the electrode assembly was put into a pouch-shaped secondary battery case, and the non-aqueous electrolyte solution for a lithium secondary battery prepared as above was injected to prepare a pouch-shaped lithium secondary battery having a driving voltage of 4.2V or more.
Example 2
(preparation of nonaqueous electrolyte solution)
LiPF is put into 6 Dissolving in a non-aqueous organic solvent to obtain LiPF 6 After that, 0.1% by weight of the compound represented by chemical formula 2a, 0.8% by weight of lithium difluorophosphate, and as a third additive, 0.5% by weight of Vinylene Carbonate (VC), 0.5% by weight of 1, 3-Propane Sultone (PS) and 1.0% by weight of ethylene sulfate (ESa) were added to prepare a nonaqueous electrolyte solution (see table 1 below).
(preparation of secondary battery)
A lithium secondary battery was fabricated in the same manner as in example 1, except that the nonaqueous electrolyte solution for a lithium secondary battery fabricated in example 1 was replaced with the nonaqueous electrolyte solution for a lithium secondary battery fabricated in the above.
Example 3
(preparation of nonaqueous electrolyte solution)
LiPF is put into 6 Dissolving in a non-aqueous organic solvent to obtain LiPF 6 After that, 0.3% by weight of the compound represented by chemical formula 2a, 1.0% by weight of lithium difluorophosphate and 0.5% by weight of ethylene carbonate as a third additive were added at a concentration of 1.0MAn olefin ester (VC), 0.5 wt% of 1, 3-Propane Sultone (PS), and 1.0 wt% of ethylene sulfate (ESa) were prepared to prepare a nonaqueous electrolyte solution (see table 1 below).
(preparation of secondary battery)
A lithium secondary battery was fabricated in the same manner as in example 1, except that the nonaqueous electrolyte solution for a lithium secondary battery fabricated in example 1 was replaced with the nonaqueous electrolyte solution for a lithium secondary battery fabricated in the above.
Example 4
(preparation of nonaqueous electrolyte solution)
LiPF is put into 6 Dissolving in a non-aqueous organic solvent to obtain LiPF 6 After that, 0.3 wt% of the compound represented by chemical formula 2a, 0.8 wt% of lithium difluorophosphate, and as a third additive, 0.5 wt% of Vinylene Carbonate (VC), 0.5 wt% of 1, 3-Propane Sultone (PS) and 1.0 wt% of ethylene sulfate (ESa) were added to prepare a nonaqueous electrolyte solution.
(preparation of secondary battery)
A lithium secondary battery was fabricated in the same manner as in example 1, except that the nonaqueous electrolyte solution for a lithium secondary battery fabricated in example 1 was replaced with the nonaqueous electrolyte solution for a lithium secondary battery fabricated in the above.
Example 5
(preparation of nonaqueous electrolyte solution)
LiPF is put into 6 Dissolving in a non-aqueous organic solvent to obtain LiPF 6 After that, 0.5% by weight of the compound represented by chemical formula 2a, 1.0% by weight of lithium difluorophosphate, and as a third additive, 0.5% by weight of Vinylene Carbonate (VC), 0.5% by weight of 1, 3-Propane Sultone (PS) and 1.0% by weight of ethylene sulfate (ESa) were added to prepare a nonaqueous electrolyte solution.
(preparation of secondary battery)
A lithium secondary battery was fabricated in the same manner as in example 1, except that the nonaqueous electrolyte solution for a lithium secondary battery fabricated in example 1 was replaced with the nonaqueous electrolyte solution for a lithium secondary battery fabricated in the above.
Example 6
(preparation of nonaqueous electrolyte solution)
LiPF is put into 6 Dissolving in a non-aqueous organic solvent to obtain LiPF 6 After that, 0.5% by weight of the compound represented by chemical formula 2a, 0.5% by weight of lithium difluorophosphate, and as a third additive, 0.5% by weight of Vinylene Carbonate (VC), 0.5% by weight of 1, 3-Propane Sultone (PS) and 1.0% by weight of ethylene sulfate (ESa) were added to prepare a nonaqueous electrolyte solution.
(preparation of secondary battery)
A lithium secondary battery was fabricated in the same manner as in example 1, except that the nonaqueous electrolyte solution for a lithium secondary battery fabricated in example 1 was replaced with the nonaqueous electrolyte solution for a lithium secondary battery fabricated in the above.
Comparative example 1
(preparation of nonaqueous electrolyte solution)
LiPF is put into 6 Dissolving in a non-aqueous organic solvent to obtain LiPF 6 After that, 0.5 wt% of Vinylene Carbonate (VC), 0.5 wt% of 1, 3-Propane Sultone (PS) and 1.0 wt% of ethylene sulfate (ESa) were added to prepare a nonaqueous electrolyte solution.
(preparation of secondary battery)
A lithium secondary battery was fabricated in the same manner as in example 1, except that the nonaqueous electrolyte solution for a lithium secondary battery fabricated in example 1 was replaced with the nonaqueous electrolyte solution for a lithium secondary battery fabricated in the above.
Comparative example 2
(preparation of nonaqueous electrolyte solution)
LiPF is put into 6 Dissolving in a non-aqueous organic solvent to obtain LiPF 6 After that, 1.0 wt% lithium difluorophosphate, 0.5 wt% Vinylene Carbonate (VC), 0.5 wt% 1, 3-Propane Sultone (PS) and 1.0 wt% ethylene sulfate (ESa) were added to prepare a nonaqueous electrolyte solution.
(preparation of secondary battery)
A lithium secondary battery was fabricated in the same manner as in example 1, except that the nonaqueous electrolyte solution for a lithium secondary battery fabricated in example 1 was replaced with the nonaqueous electrolyte solution for a lithium secondary battery fabricated in the above.
Comparative example 3
(preparation of nonaqueous electrolyte solution)
LiPF is put into 6 Dissolving in a non-aqueous organic solvent to obtain LiPF 6 After that, 0.5% by weight of the compound represented by chemical formula 2a, 0.5% by weight of Vinylene Carbonate (VC), 0.5% by weight of 1, 3-Propane Sultone (PS) and 1.0% by weight of ethylene sulfate (ESa) were added to prepare a non-aqueous electrolyte solution.
(preparation of secondary battery)
A lithium secondary battery was fabricated in the same manner as in example 1, except that the nonaqueous electrolyte solution for a lithium secondary battery fabricated in example 1 was replaced with the nonaqueous electrolyte solution for a lithium secondary battery fabricated in the above.
Comparative example 4
(preparation of nonaqueous electrolyte solution)
LiPF is put into 6 Dissolving in a non-aqueous organic solvent to obtain LiPF 6 After that, 0.5 wt% of the compound represented by the following chemical formula 3, 1.0 wt% of lithium difluorophosphate, 0.5 wt% of Vinylene Carbonate (VC), 0.5 wt% of 1, 3-Propane Sultone (PS) and 1.0 wt% of ethylene sulfate (ESa) were added to prepare a nonaqueous electrolyte solution.
[ chemical formula 3]
(preparation of secondary battery)
A lithium secondary battery was fabricated in the same manner as in example 1, except that the nonaqueous electrolyte solution for a lithium secondary battery fabricated in example 1 was replaced with the nonaqueous electrolyte solution for a lithium secondary battery fabricated in the above.
Comparative example 5
A lithium secondary battery was fabricated in the same manner as in example 2, except that Li (Ni 0.8 Mn 0.1 Co 0.1 )O 2 (hereinafter referred to as "NCM 1") instead of Li (Ni 0.85 Mn 0.08 Co 0.05 Al 0.02 )O 2 As a positive electrode active material, a positive electrode was prepared.
Comparative example 6
A lithium secondary battery was fabricated in the same manner as in example 4, except that Li (Ni 0.8 Mn 0.1 Co 0.1 )O 2 (hereinafter referred to as "NCM 1") instead of Li (Ni 0.85 Mn 0.08 Co 0.05 Al 0.02 )O 2 As a positive electrode active material, a positive electrode was prepared.
Comparative example 7
A lithium secondary battery was fabricated in the same manner as in example 3, except that Li (Ni 0.6 Mn 0.2 Co 0.2 )O 2 (hereinafter referred to as "NCM 2") instead of Li (Ni 0.85 Mn 0.08 Co 0.05 Al 0.02 )O 2 As a positive electrode active material, a positive electrode was prepared.
Comparative example 8
A lithium secondary battery was fabricated in the same manner as in example 5, except that Li (Ni 0.6 Mn 0.2 Co 0.2 )O 2 (hereinafter referred to as "NCM 2") instead of Li (Ni 0.85 Mn 0.08 Co 0.05 Al 0.02 )O 2 As a positive electrode active material, a positive electrode was prepared.
TABLE 1
In table 1, abbreviations for the respective compounds have the following meanings:
NCMA：Li(Ni 0.85 Mn 0.08 Co 0.05 Al 0.02 )O 2
NCM1：Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2
NCM2：Li(Ni 0.6 Mn 0.2 Co 0.2 )O 2
test case
Test example 1: evaluation of resistivity after high temperature storage
Each of the secondary batteries prepared in examples 1 to 6 and comparative examples 1 to 8 was charged to 4.2V at a constant current/constant voltage condition at 25 ℃ at a rate of 0.33C, and thereafter, each of the secondary batteries was discharged to 2.5V at a constant current condition at a rate of 0.33C, and the above procedure was set as one cycle. After initial charge and discharge for 3 cycles, the voltage drop value confirmed when discharged at a rate of 2.5C for 10 seconds at a SOC of 50% was measured, and the initial resistance value was calculated using the following equation 1.
Subsequently, each of the lithium secondary batteries prepared in examples 1 to 6 and comparative examples 1 to 8 was stored at 60 ℃ for 3 weeks at 100% SOC and cooled to 25 ℃, after which the voltage drop value confirmed when discharged at 50% SOC at a rate of 2.5C for 10 seconds was measured, and the resistance increase rate was calculated using the following equation 2.
[ equation 1]
Initial discharge resistance (ohm) = (pre-discharge voltage-post-discharge voltage) [ V ]/discharge current value [ a ]
[ equation 2]
Resistance increase ratio (%) = { (resistance after high temperature storage-resistance before high temperature storage)/resistance before high temperature storage) } ×100
TABLE 2
| Initial discharge resistance (milliohm) | Resistivity after high temperature storage (%) | |
| Example 1 | 36.0 | 2.9 |
| Example 2 | 36.2 | 3.6 |
| Example 3 | 38.2 | -4.3 |
| Example 4 | 38.4 | 1.3 |
| Example 5 | 42.1 | -8.6 |
| Example 6 | 41.0 | 5.1 |
| Comparative example 1 | 33.4 | 96.5 |
| Comparative example 2 | 44.1 | 49.6 |
| Comparative example 3 | 36.6 | 43.7 |
| Comparative example 4 | 39.6 | 19.5 |
| Comparative example 5 | 44.5 | 7.7 |
| Comparative example 6 | 47.0 | 4.4 |
| Comparative example 7 | 58.5 | 35.5 |
| Comparative example 8 | 61.7 | 32.9 |
Referring to table 2 above, it can be seen that the secondary batteries prepared in examples 1 to 5 exhibited greatly reduced resistivity increase (%) after high-temperature storage, compared to the lithium secondary batteries prepared in comparative examples 1 to 4 using the nonaqueous electrolyte solutions without the first additive and/or the second additive and the lithium secondary batteries prepared in comparative examples 5 to 8 having positive electrodes with different positive electrode active material compositions.
It can be understood that the secondary battery including the non-aqueous electrolyte solutions having the same contents of the first additive and the second additive prepared in example 6 exhibited a relatively increased resistance increase rate (%) after storage at high temperature because the initial film resistance was increased as compared to the batteries prepared in examples 1 to 5.
Test example 2: evaluation of initial discharge capacity and discharge capacity retention (%)
Each of the lithium secondary batteries prepared in examples 1 to 6 and comparative examples 1 to 4, 7 and 8 was charged to 4.2V at a constant current-constant voltage condition at 25 ℃ at a rate of 0.33C, and thereafter, each of the lithium secondary batteries was discharged to 2.5V at a constant current condition at a rate of 0.33C, and the above procedure was set as one cycle. After 3 cycles, the initial discharge capacity was measured, and the results are shown in table 3 below.
Subsequently, after storing at 60 ℃ for 3 weeks at 100% SOC, each of the lithium secondary batteries prepared in examples 1 to 6 and comparative examples 1 to 4, 7 and 8 was cooled to 25 ℃, and then the discharge capacity was measured. The discharge capacity retention rate was calculated using the following equation 3, and the results thereof are shown in the following table 3.
[ equation 3]
Discharge capacity retention (%) = (discharge capacity after 3 weeks of high temperature storage at 60 ℃ c/initial discharge capacity) ×100
TABLE 3
| Initial discharge capacity (mAh) | Discharge capacity retention after high temperature storage (%) | |
| Example 1 | 2034.3 | 86.5 |
| Example 2 | 2033.5 | 84.2 |
| Example 3 | 2030.2 | 93.0 |
| Examples4 | 2030.0 | 90.4 |
| Example 5 | 2025.2 | 96.3 |
| Example 6 | 2028.8 | 79.6 |
| Comparative example 1 | 2046.3 | 56.8 |
| Comparative example 2 | 1987.2 | 75.2 |
| Comparative example 3 | 2021.4 | 68.4 |
| Comparative example 4 | 2020.7 | 78.5 |
| Comparative example 7 | 1007.4 | 84.1 |
| Comparative example 8 | 1003.4 | 82.5 |
Referring to table 3 above, it can be seen that the initial discharge capacities of the secondary batteries prepared in examples 1 to 6 were increased as compared with comparative examples 2 to 4, 7 and 8.
The secondary battery of comparative example 1, in which the nonaqueous electrolyte solution contained no first and second additives, did not form a stable film, so the consumption amount of lithium ions was lower during evaluation of initial performance, as compared with the secondary battery of example, in which sufficient film can be formed because lithium ions were easily consumed. Accordingly, it can be understood that the initial discharge capacity was relatively increased as compared with the secondary batteries in examples 1 to 6.
In addition, referring to the above table 3, it can be seen that the discharge capacity retention (%) of the secondary batteries prepared in examples 1 to 5 was increased as compared to comparative examples 1 to 4, 7 and 8.
It can be understood that the secondary battery having the non-aqueous electrolyte solution having the same contents of the first additive and the second additive prepared in example 6 exhibited a relatively reduced discharge capacity retention (%) after high-temperature storage due to an increase in film resistance as compared to the batteries prepared in examples 2 to 6.
Test example 3: evaluation of volume increase rate after high temperature storage
Each of the lithium secondary batteries prepared in examples 1 to 6 and comparative examples 1 to 4 was charged to 4.2V (0.05C cut-off) at a constant current/constant voltage condition at a rate of 0.33C, after which each of the lithium secondary batteries was insulated with an imide tape, and then the initial volume was measured. The volume was calculated by measuring the weight of deionized water in and out based on archimedes' principle.
Subsequently, after storage at 60 ℃ for 3 weeks, the thickness of each lithium secondary battery after high temperature storage was measured, and the volume increase rate was calculated by introducing the measurement result into the following equation 4, the result of which is shown in the following table 4.
[ equation 4]
Volume increase rate (%) = { (volume after high temperature storage-volume before high temperature storage)/volume before high temperature storage) } ×100
TABLE 4
| Rate of volume increase (%) | |
| Example 1 | 2.9 |
| Example 2 | 3.3 |
| Example 3 | 2.0 |
| Example 4 | 2.3 |
| Example 5 | 1.3 |
| Example 6 | 3.1 |
| Comparative example 1 | 10.0 |
| Comparative example 2 | 4.6 |
| Comparative example 3 | 6.3 |
| Comparative example 4 | 4.6 |
Referring to table 4 above, it can be seen that the volume increase rate (%) of the secondary batteries of examples 1 to 6 of the present invention after high temperature storage at 60 ℃ was about 3.6% or less, and thus the volume increase rate (%) after high temperature storage was increased as compared with comparative examples 1 to 4.
Claims (10)
1. A lithium secondary battery, comprising:
a negative electrode containing a negative electrode active material,
a positive electrode containing a positive electrode active material represented by chemical formula 1,
a separator disposed between the positive electrode and the negative electrode, and
a non-aqueous electrolyte solution comprising a non-aqueous electrolyte,
wherein the non-aqueous electrolyte solution comprises: a lithium salt; a non-aqueous organic solvent; a compound represented by chemical formula 2 as a first additive; lithium difluorophosphate as a second additive:
[ chemical formula 1]
Li a Ni x Co y M 1 z M 2 w O 2
Wherein, in the chemical formula 1,
M 1 is Mn, al or a combination thereof,
M 2 is at least one selected from the group consisting of Al, zr, W, ti, M, ca and Sr, 0.8.ltoreq.a.ltoreq.1.2, 0.7.ltoreq.x<1、0<y<0.3、0<z<0.3、0.01<w≤0.2；
[ chemical formula 2]
Wherein, in chemical formula 2, R is an alkylene group having 1 to 5 carbon atoms.
2. The lithium secondary battery according to claim 1, wherein in chemical formula 1, M 2 Is selected fromAt least one of the group consisting of Al, zr, Y, M and Ti, and 0.85.ltoreq.a.ltoreq. 1.15,0.75.ltoreq.x.ltoreq. 0.99,0.001<y<0.3，0.001<z<0.25，0.01<w≤0.1。
3. The lithium secondary battery according to claim 1, wherein in chemical formula 1, M 2 Al, and a is more than or equal to 0.9 and less than or equal to 1.05,0.8 and x is more than or equal to 0.95,0.01<y<0.25，0.01≤z<0.20，0.01<w≤0.05。
4. The lithium secondary battery according to claim 1, wherein the positive electrode active material is Li (Ni 0.8 Co 0.15 Al 0.05 )O 2 、Li(Ni 0.85 Mn 0.08 Co 0.05 Al 0.02 )O 2 、Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O 2 、Li(Ni 0.87 Mn 0.07 Co 0.04 Al 0.02 )O 2 Or Li (Ni) 0.90 Mn 0.03 Co 0.05 Al 0.02 )O 2 。
5. The lithium secondary battery according to claim 1, wherein in chemical formula 2, R is an alkylene group having 1 to 3 carbon atoms.
6. The lithium secondary battery according to claim 1, wherein the compound represented by chemical formula 2 is a compound represented by chemical formula 2a,
[ chemical formula 2a ]
7. The lithium secondary battery according to claim 1, wherein the content of the compound represented by chemical formula 2 is 0.5 to 5 wt% based on the total weight of the lithium secondary battery.
8. The lithium secondary battery according to claim 1, wherein a weight ratio of the compound represented by chemical formula 2 to lithium difluorophosphate is 1:2 to 1:15.
9. The lithium secondary battery according to claim 1, wherein a weight ratio of the compound represented by chemical formula 2 to lithium difluorophosphate is 1:2 to 1:10.
10. The lithium secondary battery according to claim 1, wherein the nonaqueous electrolyte solution contains at least one of a cyclic carbonate organic solvent, a linear carbonate organic solvent, and a linear ester organic solvent, and further contains at least one selected from the group consisting of a cyclic carbonate compound, a halogenated carbonate compound, a sultone compound, a sulfate compound, a phosphate compound or a phosphite compound, a borate compound, a benzene compound, an amine compound, an imidazole compound, a silane compound, and a lithium salt compound as a third additive.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR10-2021-0133482 | 2021-10-07 | ||
| KR1020220125821A KR20230050243A (en) | 2021-10-07 | 2022-09-30 | Lithium secondary battery |
| KR10-2022-0125821 | 2022-09-30 | ||
| PCT/KR2022/014922 WO2023059037A1 (en) | 2021-10-07 | 2022-10-04 | Lithium secondary battery |
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| CN116802875A true CN116802875A (en) | 2023-09-22 |
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| CN202280011717.9A Pending CN116802875A (en) | 2021-10-07 | 2022-10-04 | Lithium secondary battery |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117810539A (en) * | 2024-03-01 | 2024-04-02 | 如鲲(江苏)新材料科技有限公司 | Electrolyte additive, nonaqueous electrolyte and lithium ion battery |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117810539A (en) * | 2024-03-01 | 2024-04-02 | 如鲲(江苏)新材料科技有限公司 | Electrolyte additive, nonaqueous electrolyte and lithium ion battery |
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