CN118073519A - Electrode for lithium secondary battery and lithium secondary battery including the same - Google Patents
Electrode for lithium secondary battery and lithium secondary battery including the same Download PDFInfo
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- CN118073519A CN118073519A CN202310876798.5A CN202310876798A CN118073519A CN 118073519 A CN118073519 A CN 118073519A CN 202310876798 A CN202310876798 A CN 202310876798A CN 118073519 A CN118073519 A CN 118073519A
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- Prior art keywords
- electrode
- active material
- secondary battery
- lithium
- electrode active
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 93
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 93
- 229910003002 lithium salt Inorganic materials 0.000 claims abstract description 129
- 159000000002 lithium salts Chemical class 0.000 claims abstract description 126
- 239000007772 electrode material Substances 0.000 claims abstract description 121
- 239000011247 coating layer Substances 0.000 claims abstract description 83
- 239000010410 layer Substances 0.000 claims abstract description 82
- 230000003746 surface roughness Effects 0.000 claims abstract description 52
- 239000002245 particle Substances 0.000 claims abstract description 34
- 238000000576 coating method Methods 0.000 claims description 45
- 239000011248 coating agent Substances 0.000 claims description 42
- 239000003792 electrolyte Substances 0.000 claims description 42
- 238000005259 measurement Methods 0.000 claims description 28
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 16
- 229910001416 lithium ion Inorganic materials 0.000 claims description 16
- 238000004128 high performance liquid chromatography Methods 0.000 claims description 15
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 6
- 229940031993 lithium benzoate Drugs 0.000 claims description 6
- AMXOYNBUYSYVKV-UHFFFAOYSA-M lithium bromide Chemical compound [Li+].[Br-] AMXOYNBUYSYVKV-UHFFFAOYSA-M 0.000 claims description 6
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 claims description 6
- IIPYXGDZVMZOAP-UHFFFAOYSA-N lithium nitrate Chemical compound [Li+].[O-][N+]([O-])=O IIPYXGDZVMZOAP-UHFFFAOYSA-N 0.000 claims description 6
- INHCSSUBVCNVSK-UHFFFAOYSA-L lithium sulfate Chemical compound [Li+].[Li+].[O-]S([O-])(=O)=O INHCSSUBVCNVSK-UHFFFAOYSA-L 0.000 claims description 6
- LDJNSLOKTFFLSL-UHFFFAOYSA-M lithium;benzoate Chemical compound [Li+].[O-]C(=O)C1=CC=CC=C1 LDJNSLOKTFFLSL-UHFFFAOYSA-M 0.000 claims description 6
- 229910011131 Li2B4O7 Inorganic materials 0.000 claims description 3
- FUJCRWPEOMXPAD-UHFFFAOYSA-N Li2O Inorganic materials [Li+].[Li+].[O-2] FUJCRWPEOMXPAD-UHFFFAOYSA-N 0.000 claims description 3
- 229910001323 Li2O2 Inorganic materials 0.000 claims description 3
- 229910013178 LiBO2 Inorganic materials 0.000 claims description 3
- 229910010878 LiIO2 Inorganic materials 0.000 claims description 3
- XUCJHNOBJLKZNU-UHFFFAOYSA-M dilithium;hydroxide Chemical compound [Li+].[Li+].[OH-] XUCJHNOBJLKZNU-UHFFFAOYSA-M 0.000 claims description 3
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims description 3
- 229910052808 lithium carbonate Inorganic materials 0.000 claims description 3
- 229910001386 lithium phosphate Inorganic materials 0.000 claims description 3
- GKQWYZBANWAFMQ-UHFFFAOYSA-M lithium;2-hydroxypropanoate Chemical compound [Li+].CC(O)C([O-])=O GKQWYZBANWAFMQ-UHFFFAOYSA-M 0.000 claims description 3
- AZVCGYPLLBEUNV-UHFFFAOYSA-N lithium;ethanolate Chemical compound [Li+].CC[O-] AZVCGYPLLBEUNV-UHFFFAOYSA-N 0.000 claims description 3
- XAVQZBGEXVFCJI-UHFFFAOYSA-M lithium;phenoxide Chemical compound [Li+].[O-]C1=CC=CC=C1 XAVQZBGEXVFCJI-UHFFFAOYSA-M 0.000 claims description 3
- GRVDJDISBSALJP-UHFFFAOYSA-N methyloxidanyl Chemical compound [O]C GRVDJDISBSALJP-UHFFFAOYSA-N 0.000 claims description 3
- TWQULNDIKKJZPH-UHFFFAOYSA-K trilithium;phosphate Chemical compound [Li+].[Li+].[Li+].[O-]P([O-])([O-])=O TWQULNDIKKJZPH-UHFFFAOYSA-K 0.000 claims description 3
- HAUKUGBTJXWQMF-UHFFFAOYSA-N lithium;propan-2-olate Chemical compound [Li+].CC(C)[O-] HAUKUGBTJXWQMF-UHFFFAOYSA-N 0.000 claims description 2
- 229910001216 Li2S Inorganic materials 0.000 claims 1
- 239000006183 anode active material Substances 0.000 description 17
- 239000011230 binding agent Substances 0.000 description 15
- 239000007774 positive electrode material Substances 0.000 description 15
- 239000007773 negative electrode material Substances 0.000 description 14
- 230000000052 comparative effect Effects 0.000 description 13
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 12
- DTQVDTLACAAQTR-UHFFFAOYSA-N Trifluoroacetic acid Chemical compound OC(=O)C(F)(F)F DTQVDTLACAAQTR-UHFFFAOYSA-N 0.000 description 12
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 11
- 238000000034 method Methods 0.000 description 10
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- 238000007086 side reaction Methods 0.000 description 9
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- -1 lithium salt compound Chemical class 0.000 description 8
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- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
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- 229910021450 lithium metal oxide Inorganic materials 0.000 description 2
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- SJHAYVFVKRXMKG-UHFFFAOYSA-N 4-methyl-1,3,2-dioxathiolane 2-oxide Chemical compound CC1COS(=O)O1 SJHAYVFVKRXMKG-UHFFFAOYSA-N 0.000 description 1
- 229910000838 Al alloy Inorganic materials 0.000 description 1
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- 229910018279 LaSrMnO Inorganic materials 0.000 description 1
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Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Battery Electrode And Active Subsutance (AREA)
Abstract
An electrode for a lithium secondary battery includes an electrode current collector, an electrode active material layer formed on at least one surface of the electrode current collector and including electrode active material particles, and a coating layer containing a lithium salt formed on at least a portion of the surface of the electrode active material particles or at least a portion of the surface of the electrode active material layer. The electrode for the lithium secondary battery may have a predetermined surface roughness.
Description
Cross Reference to Related Applications
The present application claims priority from korean patent application No. 10-2022-0157578 and korean patent application No. 10-2023-0028636, filed on day 2022, 11 and 22, respectively, and filed on day 2023, 3 and 3, the disclosures of which are incorporated herein by reference in their entireties.
Technical Field
The present invention relates to an electrode for a lithium secondary battery and a lithium secondary battery including the same. More particularly, the present invention relates to an electrode for a lithium secondary battery including an electrode active material, and a lithium secondary battery including the same.
Background
The secondary battery is a battery that can be repeatedly charged and discharged, and is widely used in portable electronic communication devices such as video cameras, mobile phones, notebook computers, and the like with the development of information communication industry and display industry. Examples of the secondary battery may include lithium secondary batteries, nickel cadmium batteries, nickel hydrogen batteries, and the like. Among them, the lithium secondary battery has a high operating voltage and a high energy density per unit weight, and is advantageous in terms of charging speed and light weight. In this regard, lithium secondary batteries have been actively developed and used as a power source.
The lithium secondary battery may include an electrode assembly including a positive electrode, a negative electrode, and a separator, and an electrolyte to immerse the electrode assembly. In addition, the lithium secondary battery may further include a case having, for example, a soft-pack shape (pouch-shaped) for accommodating the electrode assembly and an electrolyte is enclosed in the case.
For example, the electrode may include electrode active material particles capable of intercalating (INTERCALATING) and Deintercalating (DEINTERCALATING) lithium ions. When the secondary battery is repeatedly charged/discharged, mechanical and chemical damage such as particle breakage (crack) may occur, and contact between active material particles may be deteriorated and a short circuit may occur.
When the composition and structure of the electrode active material are changed to improve the stability of the active material particles, the electrical conductivity (conductivity) may be reduced, resulting in a decrease in the output (output) of the secondary battery. Therefore, it is required to develop a secondary battery electrode capable of securing life stability and output/capacity characteristics.
For example, korean patent laid-open publication No. 2017-0099748 discloses an electrode assembly for a lithium secondary battery and a lithium secondary battery including the same, but has limitations in securing sufficient high rate and high capacity characteristics.
Disclosure of Invention
According to one aspect of the present invention, there is provided an electrode for a lithium secondary battery having improved electrical properties and stability.
According to an aspect of the present invention, there is provided a lithium secondary battery including the electrode having improved electrical properties and stability.
In order to achieve the above object, according to one aspect of the present invention, there is provided an electrode for a lithium secondary battery, including an electrode current collector; an electrode active material layer disposed on at least one surface of the electrode current collector and including electrode active material particles; and a lithium salt-containing coating layer formed on at least a portion (at least portions) of the surface of the electrode active material particle and/or at least a portion of the surface of the electrode active material layer, wherein the electrode has an arithmetic average value (Ra) of surface roughness represented by the following formula 1:
[ 1]
Ra≤25nm
In formula 1, ra is a value obtained by calculating an arithmetic average of surface roughness values measured in 20 or more measurement areas for an electrode surface of a lithium secondary battery in a scanning range of 0.5 μm×0.5 μm using an atomic force microscope.
For example, the arithmetic average (Ra) of the surface roughness may be 0.1nm to 25nm.
In some embodiments, the surface roughness value measured in each measurement region may be an arithmetic average of surface roughness values excluding a maximum value and a minimum value from roughness values measured for each measurement region 15 times or more in a scanning range of 0.5 μm×0.5 μm.
In some embodiments, the standard deviation of the surface roughness value measured in the measurement region for the electrode surface of the lithium secondary battery may be 2.5nm or less.
In some embodiments, the lithium salt-containing coating layer may have a continuous film shape (continuous FILM SHAPE) covering the surface of the electrode active material particle or the surface of the electrode active material layer.
In some embodiments, the thickness of the lithium salt-containing coating may be from 1nm to 1000nm.
In some embodiments, the lithium salt-containing coating may include at least one of ：LiCl、LiF、Li3PO4、LiBO2、LiIO2、Li2CO3、Li2B4O7、Li2SO4、LiBr、LiI、LiNO3、Li(CF3CO2)、Li((CH3)3SiO)、Li(CH3O)、LiCH3COO、Li(CO2CH3)、(CH3)2CHOLi( lithium isopropoxide), CH 3 CH (OH) coli (lithium lactate), li 2S、LiOH、Li2O、Li2O2、CH3CH2 OLi (lithium ethoxide), C 6H5 OLi (lithium phenoxide), and/or C 7H5LiO2 (lithium benzoate).
In some embodiments, the content of the lithium salt-containing coating layer may be 20ppm to 600ppm as measured by High Performance Liquid Chromatography (HPLC) based on the total weight of the electrode active material layer.
In some embodiments, a coating layer containing a lithium salt may be formed on both the surface of the electrode active material particles and the surface of the electrode active material layer.
In some embodiments, the lithium ion conductivity (lithium ion conductivity) of the lithium salt-containing coating may be 1 x 10 -7 S/cm or greater and the electron conductivity (electronic conductivity) may be 1 x 10 -5 S/cm or less.
In some embodiments, the electrode for a lithium secondary battery may be a negative electrode or a positive electrode.
According to another aspect of the present invention, there is provided a lithium secondary battery including: a positive electrode; and a negative electrode disposed opposite to the positive electrode, wherein at least one of the positive electrode and the negative electrode is the electrode for a lithium secondary battery described above.
In some embodiments, the lithium secondary battery may further include an electrolyte impregnating the positive electrode and the negative electrode, wherein the lithium salt-containing coating layer has a solubility of 1g/L or less in the electrolyte.
The electrode for a lithium secondary battery according to an exemplary embodiment may include a coating layer containing a lithium salt formed on the surface of the electrode active material and/or the surface of the electrode active material layer. The lithium salt-containing coating layer can inhibit direct contact between the electrode active material and the electrolyte, and can prevent volume expansion and structural collapse of the electrode active material.
The electrode for a lithium secondary battery may have an arithmetic average value of predetermined surface roughness. Therefore, side reactions between the electrode active material and the electrolyte can be further suppressed. Accordingly, consumption of electrolyte and irreversible capacity loss can be reduced, and the rapid charge performance and cycle performance of the lithium secondary battery can be improved.
The lithium salt-containing coating layer has high lithium ion conductivity and low electron conductivity, and thus, life characteristics and structural stability of the electrode active material can be improved even in repeated charge/discharge behavior under extremely high temperature/high humidity conditions. Accordingly, the durability and the charge/discharge capacity of the lithium secondary battery can be improved without reducing the initial efficiency and the high charge rate.
Drawings
Fig. 1 is a schematic view showing an electrode active material having a coating layer containing a lithium salt according to an exemplary embodiment;
Fig. 2 is a schematic cross-sectional view illustrating an electrode for a lithium secondary battery according to an exemplary embodiment;
Fig. 3 is a schematic plan view (plan view) showing a lithium secondary battery according to an exemplary embodiment;
Fig. 4 is a schematic cross-sectional view illustrating an electrode assembly according to an exemplary embodiment;
Fig. 5 is a graph showing the distribution of the surface roughness values measured on the anode according to example 4 and comparative example 1;
Fig. 6 is an Atomic Force Microscope (AFM) image showing the electrode surface for a lithium secondary battery according to example 4;
Fig. 7 is an Atomic Force Microscope (AFM) image showing the electrode surface for a lithium secondary battery according to comparative example 1.
Detailed Description
According to an embodiment of the present invention, there is provided an electrode for a lithium secondary battery, which includes a coating layer containing a lithium salt and has an arithmetic average value of predetermined surface roughness.
Further, there is provided a lithium secondary battery including the above electrode for a lithium secondary battery.
Various features of the disclosed technology will be described in detail below with reference to embodiments and accompanying drawings.
As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.
For the purposes of this specification, unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, dimensions, physical characteristics, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". Unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors resulting from the standard deviation found in their respective testing measurements. Unless specifically defined otherwise in the present specification, numerical values outside the numerical range that may occur due to experimental error or rounding off also fall within the numerical range that is defined. For example, a range of "1 to 10" is intended to include any and all subranges between and including the minimum value of 1 and the maximum value of 10, i.e., all subranges beginning with a minimum value equal to or greater than 1 and ending with a maximum value of equal to or less than 10, and all subranges therebetween, e.g., 1 to 6.3 or 5.5 to 10 or 2.7 to 6.1.
The expression "comprising" as used herein is intended to mean as an open transition phrase, the meaning of which is equivalent to "comprising," "including," "having," or "characterized by … …," and does not exclude elements, materials, or steps, all of which are not described in further detail herein.
< Electrode for lithium Secondary Battery >
An electrode for a lithium secondary battery may include an electrode current collector and an electrode active material layer disposed on at least one surface of the electrode current collector and including electrode active material particles. The lithium salt-containing coating layer may be formed on the surface of the electrode active material particles and/or the surface of the electrode active material layer.
For example, a coating layer containing lithium salt may be formed on at least a portion of the surface of the electrode active material. For example, a coating layer containing a lithium salt may be formed on at least a portion of the surface of the electrode active material layer.
The lithium salt-containing coating layer is formed on the surface of the electrode active material and/or the surface of the electrode active material layer, so that the electrode active material particles can be prevented from being directly exposed to the electrolyte. Therefore, side reactions between the electrode active material particles and the electrolyte can be suppressed, thereby preventing irreversible decomposition of the electrolyte.
According to an exemplary embodiment, an electrode for a lithium secondary battery may have an arithmetic average value (Ra) of surface roughness represented by the following formula 1.
[ 1]
Ra≤25nm
In formula 1, the arithmetic average value of the surface roughness (Ra) can be obtained by measuring the surface roughness value at the surface of the electrode active material layer in a scanning range of 0.5 μm×0.5 μm using an Atomic Force Microscope (AFM).
The scanning range of 0.5 μm×0.5 μm may be a range of a portion of the electrode surface for the lithium secondary battery or a portion of the electrode active material particle surface designated in the surface direction of the electrode active material layer when the surface of the electrode active material layer is observed with an Atomic Force Microscope (AFM).
For example, ra of an electrode for a lithium secondary battery may be an arithmetic average value of surface roughness values measured at a predetermined region of a surface of an electrode active material layer using an Atomic Force Microscope (AFM).
In one embodiment, ra of an electrode for a lithium secondary battery may be obtained by measuring surface roughness values of at least three regions of the electrode. For example, an arithmetic average value (Ra) of the surface roughness may be obtained by measuring a surface roughness value of each region by selecting three or more regions of the surface of the electrode active material layer, and calculating an arithmetic average value of the measured surface roughness values.
In one embodiment, the arithmetic average of the measured surface roughness (Ra) may be performed by arbitrarily (randomly) specifying 15 or more regions, 30 or more regions, 45 or more regions, 100 or more regions, or 100 to 1000 regions of the surface of the electrode active material layer. As the number of measurement areas increases, the accuracy and reliability of the measurement can be further improved. The area of each measurement region may be about 20 μm by about 20 μm in size.
In one embodiment, the surface roughness value of each measurement area may be obtained by measuring the roughness value of the measurement area a plurality of times in a scanning range of 0.5 μm×0.5 μm, and calculating an arithmetic average of the measured roughness values.
For example, the surface roughness value may be obtained from electrode active material particles present in each measurement region, and may refer to center line average roughness in a direction perpendicular to the surface of the measurement region.
The roughness value of each measurement area can be measured in several directions of each measurement area. For example, the surface roughness value of the measurement area may be obtained by measuring the roughness value in the measurement area in each of 15 or more directions and calculating an arithmetic average of the measured roughness values. For example, the roughness value of each measurement area may be measured 15 times or more, 30 times or more, or 50 to 200 times in several directions. The measurement direction in the measurement area may be randomly selected.
In one embodiment, the surface roughness value of each measurement region may be obtained by calculating an arithmetic average of roughness values excluding one maximum value and one minimum value among the measured roughness values in consideration of measurement errors and dispersion (dispersion).
Since the electrode for a lithium secondary battery has an arithmetic average value of surface roughness in the above range, the surface area of the electrode exposed to an electrolyte can be reduced, and side reactions in the electrode can be suppressed, thereby improving life characteristics.
For example, when the surface roughness of the electrode active material and/or the electrode active material layer is high, the surface area exposed to the electrolyte may increase due to the uneven structure. Accordingly, side reactions between the electrolyte and the electrode active material may increase, and structural collapse of the electrode active material and exhaustion of the electrolyte may occur due to repeated charge and discharge.
The lithium salt-containing coating layer is formed on the surface of the electrode active material particles and/or the surface of the electrode active material layer, and the arithmetic average value of the surface roughness of the electrode for the lithium secondary battery is adjusted within the above-described range, whereby the side reaction between the electrode active material and the electrolyte can be further suppressed.
For example, since the arithmetic average value of the surface roughness of the electrode active material is reduced, contact between the electrode active material and the electrolyte can be suppressed, and since the electron conductivity is reduced by the lithium salt-containing coating layer, side reactions of the electrode active material and the electrolyte can be prevented. Furthermore, the arithmetic average of the surface roughness can be easily adjusted by the lithium salt-containing coating.
In some embodiments, the arithmetic average of the surface roughness of the electrode for a lithium secondary battery may be 0.001nm to 25nm, or 0.1nm to 21nm. Within the above range, the surface of the electrode active material layer may easily form a stable solid electrolyte interface (solid electrolyte interface, SEI) layer during initial driving, and the reactivity between the electrode active material and the electrolyte may be further reduced. Therefore, by further preventing collapse/regeneration (collapse/reproduction) of the SEI layer during repeated charge and discharge and consumption of an electrolyte due to the same reasons, the life characteristics of the battery can be more improved.
In some embodiments, the standard deviation of the surface roughness value measured in the measurement region for the electrode surface of the lithium secondary battery may be 2.5nm or less. For example, the standard deviation may be less than 2.5nm,2.3nm or less, or 2.0nm or less.
The standard deviation may be an index representing uniformity of surface roughness of an electrode for a lithium secondary battery. For example, since the surface roughness value measured in an arbitrary region of the surface of the electrode for a lithium secondary battery has a low standard deviation or a narrow distribution, the roughness deviation between local regions can be reduced.
For example, as the standard deviation increases, a portion of the area of the electrode surface may have a relatively high roughness. Therefore, since the reaction between the electrode active material and the electrolyte may be concentrated in the corresponding region, the structural stability of the electrode and the life characteristics of the electrode active material may be relatively degraded.
According to the exemplary embodiment, since both the arithmetic average value (Ra) of the surface roughness and the standard deviation of the surface roughness value measured from the electrode surface for a lithium secondary battery have low values, the surface of the electrode may have low and uniform roughness as a whole. Accordingly, the stability and life characteristics of the lithium secondary battery may be further improved.
In some embodiments, the lithium salt-containing coating layer may cover at least a portion of the surface of the electrode active material and/or at least a portion of the surface of the electrode active material layer. For example, the lithium salt-containing coating layer may have a continuous film shape, and the lithium salt-containing coating layer covers part or all of the surface of the electrode active material and/or part or all of the surface of the electrode active material layer.
Fig. 1 is a schematic cross-sectional view illustrating an electrode active material included in an electrode for a lithium secondary battery according to an exemplary embodiment.
Referring to fig. 1, an electrode for a lithium secondary battery may include electrode active material particles 10 and a coating layer 12 containing a lithium salt surrounding the surface of the electrode active material particles 10.
Since the lithium salt-containing coating layer 12 is formed on the surface of the electrode active material particles 10, direct contact between the electrode active material particles 10 and the electrolyte can be prevented, and mechanical/thermal shock from the outside can be alleviated. Therefore, structural defects and damages of the electrode active material particles 10 can be prevented.
For example, the lithium salt-containing coating 12 may be formed by a wet coating process (wet coating method). For example, the coating layer 12 containing lithium salt may be formed on the surface of the electrode active material particles 10 by mixing and stirring a mixed solution containing lithium salt and an organic solvent with the electrode active material particles 10, and then drying the mixture to evaporate the organic solvent. A heat treatment step may be additionally performed after the drying.
Fig. 2 is a schematic cross-sectional view illustrating an electrode for a lithium secondary battery according to an exemplary embodiment.
Referring to fig. 2, an electrode 20 for a lithium secondary battery may include an electrode current collector 22, an electrode active material layer 24 formed on at least one surface of the electrode current collector 22, and a coating layer 26 containing a lithium salt covering at least a portion of the surface of the electrode active material layer 24.
In some embodiments, the electrode active material layer 24 may be formed on both surfaces of the electrode current collector 22. For example, the electrode active material layer 24 may be coated on the upper and lower surfaces of the electrode current collector 22, respectively. The electrode active material layer 24 may be directly coated on the surface of the electrode current collector 22.
The lithium salt-containing coating layer 26 may be formed to cover the electrode active material layer 24. For example, the lithium salt-containing coating 26 may be formed by a wet coating method.
In one embodiment, the lithium salt-containing coating layer 26 may be formed by applying a mixed solution including a lithium salt and an organic solvent to the electrode active material layer 24, and then drying the mixture. A heat treatment step may be additionally performed after the drying.
In one embodiment, the lithium salt-containing coating layer 26 may be formed on the electrode active material layer 24 by immersing the electrode active material layer 24 in a solution in which the lithium salt is dissolved, and then taking out the electrode active material layer 24 and drying. A heat treatment step may be additionally performed after the drying.
In some embodiments, the thickness of the lithium salt-containing coating may be 1nm to 1000nm, for example 1nm to 500nm.
Within the above range, consumption of the electrolyte and oxidation/reduction of the electrode active material due to contact between the electrode active material and the electrolyte can be more suppressed. In addition, since a lithium movement path (lithium movement path) in the lithium salt-containing coating layer is shortened, ion conductivity may be improved, and the lithium secondary battery may have higher initial efficiency and charge/discharge capacity.
For example, if the thickness of the lithium salt-containing coating layer is less than 1nm, it may be relatively difficult to block permeation (permeation) of the electrolyte due to the thin coating layer, and side reactions between the electrode active material and the electrolyte may not be effectively suppressed. If the thickness of the lithium salt-containing coating layer is greater than 1000nm, the resistance may be relatively increased due to the thicker formed coating layer, and the initial efficiency and performance of the lithium secondary battery may be relatively lowered.
In some embodiments, a coating layer containing lithium salt may be formed on both the surface of the electrode active material particles and the surface of the electrode active material layer. For example, the lithium salt-containing coating may include a first lithium salt-containing coating (first lithium salt-containing coating) covering the surface of the electrode active material particles and a second lithium salt-containing coating (second lithium salt-containing coating) covering the surface of the electrode active material layer. In one embodiment, the first lithium salt-containing coating and the second lithium salt-containing coating may comprise the same lithium salt compound, or may comprise different lithium salt compounds.
Since the lithium salt-containing coating layer is formed on both the surface of the electrode active material particles and the surface of the electrode active material layer, the penetration of the electrolyte into the electrode active material particles is doubly blocked (double blocked), thereby further improving the life characteristics. Further, since high ion conductivity can be ensured, output characteristics and charge/discharge capacity can be further improved.
In some embodiments, portions of the lithium salt-containing coating may be distributed (individually distributed) alone and disposed in islands (ISLAND SHAPE) on the surface of the electrode active material and/or on the surface of the electrode active material layer.
In one embodiment, the lithium salt-containing coating layer may be disposed in a region of 90% or more of the surface of the electrode active material, or in a region of 90% or more of the surface of the electrode active material layer, for example, in a region of 95% or more, or 99% or more. Accordingly, it is possible to prevent degradation of the electrode active material due to external environment and charge/discharge while maintaining high lithium ion conductivity, thereby further improving initial efficiency and capacity retention rate.
In some embodiments, the lithium salt-containing coating may include a lithium salt having low solubility and swelling characteristics (SWELLING CHARACTERISTICS) in an organic solvent. Thus, the lithium salt-containing coating may have low reactivity to the electrolyte, high insulation and improved mechanical/chemical stability.
For example, since lithium salts have low electron conductivity and high stability even under extremely high temperature/high humidity conditions, side reactions between the electrode active material and the electrolyte can be suppressed. Accordingly, oxidation/reduction of the electrode active material by the electrolyte can be prevented, and structural collapse and rupture (ack) of the electrode active material due to driving at high temperature/high voltage and external physical impact can be prevented.
The lithium salt can increase the rate of intercalation and deintercalation of lithium ions, and thus, can prevent irreversible reactions occurring during high-speed charging and capacity loss due to overvoltage. In addition, capacity retention and cycle characteristics can be improved while improving initial efficiency and high-speed charge characteristics due to high conductivity of lithium ions and low reactivity to an electrolyte.
For example, the lithium salt-containing coating may include more than one of the following lithium ：LiCl、LiF、Li3PO4、LiBO2、LiIO2、Li2CO3、Li2B4O7、Li2SO4、LiBr、LiI、LiNO3、Li(CF3CO2)、Li((CH3)3SiO)、Li(CH3O)、LiCH3COO、Li(CO2CH3)、(CH3)2CHOLi( isopropoxides), CH 3 CH (OH) coli (lithium lactate), li 2S、LiOH、Li2O、Li2O2、CH3CH2 OLi (lithium ethoxide), C 6H5 OLi (lithium phenoxide), and/or C 7H5LiO2 (lithium benzoate), and/or the like. These may be used alone or in combination of two or more thereof.
In one embodiment, the lithium salt-containing coating may include C 7H5LiO2 (lithium benzoate). C 7H5LiO2 has low reactivity to an electrolyte or an organic solvent and high transport capacity (transport capacity) for lithium ions, so that the charge characteristics and life characteristics of the lithium secondary battery can be further improved.
In some embodiments, the lithium salt-containing coating may consist of a lithium salt. For example, the lithium salt-containing coating may not include a polymer component or polymer, such as a binder resin (binder resin). In this case, a decrease in the conductivity of lithium ions and an increase in resistance due to other components (e.g., polymer components or polymers) can be prevented, and the electrochemical characteristics of the lithium secondary battery can be further improved.
In some embodiments, the content of the lithium salt-containing coating layer may be 20ppm or more based on the total weight of the electrode active material layer. The content of the lithium salt-containing coating may be measured by High Performance Liquid Chromatography (HPLC) analysis.
For example, the ratio of the lithium salt-containing coating layer to the electrode active material can be calculated by analyzing the peak area (e.g., peak area%) of the lithium salt compound measured by HPLC analysis.
If the content of the lithium salt-containing coating layer measured by the HPLC peak area is less than 20ppm, the lithium salt-containing coating layer may be substantially absent on the surface of the electrode active material or the surface of the electrode active material layer. For example, a peak area of less than 20ppm may be a value measured from byproducts generated from the electrolyte or the cathode.
In one embodiment, the content of the lithium salt-containing coating layer may be about 20ppm to 600ppm,50ppm to 600ppm, or 100ppm to 450ppm, as measured by HPLC, based on the total weight of the electrode active material layer. The above range may be the content measured during formation of the lithium secondary battery or after initial charge and discharge. For example, the content of the lithium salt-containing coating layer measured after the lithium secondary battery is fully charged and discharged may be 20ppm to 600ppm.
Within the above range, the coating coverage (coating coverage rate) of the electrode active material or electrode active material layer can be improved while further suppressing the increase in resistance due to the lithium salt-containing coating.
For example, when the content of the lithium salt-containing coating layer contained in the electrode, measured after initial charge and discharge, is greater than 600ppm based on the total weight of the electrode active material layer, the capacity and energy density of the lithium secondary battery may be relatively reduced.
In some embodiments, the content of the lithium salt-containing coating layer measured before the formation process (formation process) of the lithium secondary battery or before the initial charge and discharge may be 0.005 to 10 parts by weight based on 100 parts by weight of the electrode active material layer, and may be, for example, 0.01 to 5 parts by weight.
For example, if the content of the lithium salt-containing coating layer measured before the formation process (formation process) is less than 0.005 parts by weight, coating coverage may be reduced due to decomposition of the lithium salt-containing coating layer occurring during initial charge and discharge, and life characteristics and stability of an electrode for a lithium secondary battery may be relatively reduced.
For example, if the content of the lithium salt-containing coating layer measured before the formation process is more than 10 parts by weight, a thick film may be formed on the electrode active material during initial charge and discharge, resulting in an increase in internal resistance (INTERNAL RESISTANCE) and a relative decrease in electrochemical performance.
In one embodiment, the content of the lithium salt-containing coating layer in the electrode active material layer may be measured by High Performance Liquid Chromatography (HPLC) analysis. For example, a 0.5 gram sample of electrode active material, which is obtained from an electrode active material layer and has a coating layer containing a lithium salt formed thereon, may be added to 10 grams Deionized (DI) water containing 0.1% trifluoroacetic acid (TFA), and then subjected to ultrasonic extraction (ultrasonic extraction) for 20 minutes. Thereafter, the sample may be pretreated by mixing the extracted solution for 12 hours and filtering the mixture using a syringe filter (SYRINGE FILTER) (Whatman company, 67502502). The pretreated sample may then be subjected to HPLC analysis under the following analytical conditions to measure the content of the lithium salt-containing coating. The specific compounds corresponding to each peak in the HPLC profile can be analyzed by MS detector.
< Conditions for HPLC analysis >
I) The device comprises: AGILENT HPLC 1200 module 1200
Ii) Column (Column): agilent C18,5 μm,150 x 4.6mm
Iii) Chromatographic column heater temperature: 30 DEG C
Iv) eluent: water (containing 0.1% trifluoroacetic acid): acetonitrile=9: 1
V) wavelength: 230nm
Vi) flow rate: 1.0 ml/min
Vii) injection amount: 30 μl
Viii) MS detector: thermo Scientific company, LTQ XL type
In some embodiments, the lithium salt-containing coating may be in the form of a solid electrolyte (solid electrolyte) having high lithium ion conductivity and low electron conductivity. For example, a coating containing a lithium salt may have a lithium ion conductivity of 1X 10 -7 S/cm or more and an electron conductivity of 1X 10 -5 S/cm or less. For example, lithium ion conductivity and electron conductivity can be calculated by measuring resistance by electrochemical impedance spectroscopy (electrochemical impedance spectroscopy EIS) and then converting it to thickness and area of the lithium salt-containing coating.
In one embodiment, the lithium ion conductivity of the lithium salt-containing coating may be 1×10 -7 S/cm to 1×10 - 2 S/cm, for example, 1×10 -6 S/cm to 1×10 -2 S/cm. Since the lithium salt-containing coating layer has high lithium ion conductivity, an increase in resistance in the coating layer can be suppressed, and thus the life characteristics, initial efficiency, and stability of the secondary battery can be further improved.
In one embodiment, the electron conductivity of the lithium salt-containing coating may be 1X 10 -9 S/cm or less, for example, 1X 10 -10 S/cm or less. Since the lithium salt-containing coating layer has the above-described low electron conductivity, oxidation/reduction or side reaction of the electrode active material can be prevented, and the cycle characteristics (CYCLE CHARACTERISTICS) and the operation stability (operation stability) of the lithium secondary battery can be further improved.
In some embodiments, an electrode for a lithium secondary battery may be a positive electrode including a positive electrode active material. For example, the electrode current collector may be a positive electrode current collector, and the electrode active material layer may be a positive electrode active material layer.
In some embodiments, an electrode for a lithium secondary battery may be a negative electrode including a negative electrode active material. For example, the electrode current collector may be a negative electrode current collector, and the electrode active material layer may be a negative electrode active material layer.
In some embodiments, the positive electrode active material may include a lithium metal oxide, for example, lithium (Li) -nickel (Ni) oxide or a lithium iron phosphate compound (lithium iron phosphate compound, liFePO 4). For example, lithium (Li) -nickel (Ni) oxide contained in the positive electrode active material layer may be represented by the following chemical formula 1.
[ Chemical formula 1]
Li1+aNi1-(x+y)CoxMyO2
In chemical formula 1, a, x and y may be in the range of-0.05.ltoreq.a.ltoreq.0.15, 0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, 0.ltoreq.x+y.ltoreq.1, respectively, and M may be one or more elements selected from the group consisting of Mg, sr, ba, B, al, si, mn, ti, zr and W, and in one embodiment, x and y may be in the range of 0.01.ltoreq.x.ltoreq.0.2, 0.01.ltoreq.y.ltoreq.0.2, respectively.
In one embodiment, in chemical formula 1, M may be manganese (Mn). In this case, nickel-cobalt-manganese (NCM) oxide may be used as the positive electrode active material.
In some embodiments, the anode active material may include carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, and the like; a lithium alloy; silicon and/or tin.
Examples of amorphous carbon may include hard carbon, coke, mesophase Carbon Microbeads (MCMB), mesophase pitch-based carbon fibers (MPCF), and/or the like.
Examples of crystalline carbon may include graphite-based carbon such as natural graphite, graphite coke, graphite MCMB, graphite MPCF, and/or the like. As the element contained In the lithium alloy, al, zn, bi, cd, at, si, pb, sn, ga or In can be used.
< Lithium Secondary Battery >
The lithium secondary battery according to the exemplary embodiment may include a positive electrode and a negative electrode disposed opposite the positive electrode, and the electrode for the lithium secondary battery including the coating layer containing the lithium salt may be at least one or both of the positive electrode and the negative electrode. For example, a coating containing a lithium salt may be included in the positive electrode or in the negative electrode. For example, a coating containing lithium salt may be included in the positive electrode and the negative electrode.
Fig. 3 and 4 are a schematic top view and a sectional view, respectively, illustrating a secondary battery according to an exemplary embodiment. For example, FIG. 4 is a cross-sectional view taken on line I-I' shown in FIG. 3.
Referring to fig. 3 and 4, the secondary battery may include an electrode assembly 150 and a case 160 accommodating the electrode assembly 150. The electrode assembly 150 may include a positive electrode 100, a negative electrode 130, and a separator 140.
The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110 formed on at least one surface of the positive electrode current collector 105. In one embodiment, the above-described lithium salt-containing coating layer may be formed on at least a portion of the surface of the positive electrode active material layer 110.
In some embodiments, the positive electrode active material layer 110 may be formed on both surfaces (e.g., upper and lower surfaces) of the positive electrode current collector 105. For example, the positive electrode active material layer 110 may be coated on the upper and lower surfaces of the positive electrode current collector 105, respectively, or may be directly coated on the surface of the positive electrode current collector 105.
The positive electrode current collector 105 may include, for example, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably includes aluminum or an aluminum alloy.
In some embodiments, in the case of the positive electrode active material layer 110, a positive electrode slurry may be coated on the positive electrode current collector 105, followed by drying and calendaring to form the positive electrode active material layer 110. For example, the positive electrode slurry may be prepared by mixing a positive electrode active material with a binder, a conductive material, and/or a dispersant in a solvent, and then stirring. In some embodiments, the above-described lithium salt-containing coating layer may be formed on at least a portion of the surface of the positive electrode active material.
The binder may include, for example, an organic binder such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc., or an aqueous binder (aqueous binder) such as Styrene Butadiene Rubber (SBR), and the binder may be used together with a thickener such as carboxymethyl cellulose (CMC).
For example, PVDF-based binders may be used as the binder for forming the positive electrode. In this case, the amount of the binder used to form the positive electrode active material layer 110 may be reduced, and the amount of the positive electrode active material or the amount of lithium metal oxide particles may be relatively increased. Thereby, the output and capacity of the secondary battery can be further improved.
A conductive material may be included to facilitate electron transfer (electron transfer) between the active material particles. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene and/or carbon nanotubes and/or metal-based conductive materials such as tin, tin oxide, titanium oxide, and/or perovskite materials such as LaSrCoO 3 or LaSrMnO 3, and the like.
In some embodiments, the positive electrode 100 may have an electrode density of 3.0 grams/cubic centimeter (g/cc) to 3.9g/cc, and for example, 3.2g/cc to 3.8g/cc.
The anode 130 may include an anode current collector 125 and an anode active material layer 120 formed on at least one surface of the anode current collector 125. In some embodiments, a coating layer containing a lithium salt may be formed on at least a portion of the surface of the anode active material layer 120.
In some embodiments, the anode active material layer 120 may be formed on both surfaces (e.g., upper and lower surfaces) of the anode current collector 125. The anode active material layer 120 may be coated on the upper and lower surfaces of the anode current collector 125, respectively, and may be in direct contact with the surface of the anode current collector 125.
Negative current collector 125 may include gold, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, and preferably includes copper or copper alloys.
In some embodiments, in the case of the anode active material layer 120, an anode slurry may be applied (coated) onto the anode current collector 125, and then dried and rolled to form the anode active material layer 120. For example, the anode slurry may be prepared by mixing the anode active material with a binder, a conductive material, and/or a dispersant in a solvent, followed by stirring. In some embodiments, the above-described lithium salt-containing coating layer may be formed on at least a portion of the surface of the anode active material.
A material substantially the same as or similar to the material used to form the positive electrode 100 may be used as the binder and the conductive material. In some embodiments, the binder used to form the anode 130 may include, for example, styrene Butadiene Rubber (SBR) or an acrylic binder to be compatible with the graphite-based active material, and may be used together with a thickener such as carboxymethyl cellulose (CMC).
In some embodiments, the anode active material layer 120 may have a density of 1.4g/cc to 1.9 g/cc.
In some embodiments, the area (e.g., the contact area with separator 140) and/or volume of negative electrode 130 may be greater than the area and/or volume of positive electrode 100. Accordingly, lithium ions generated from the positive electrode 100 can smoothly move to the negative electrode 130 without being deposited in the middle (PRECIPITATED), so that output and capacity characteristics can be further improved.
Separator 140 may be interposed between positive electrode 100 and negative electrode 130. The separator 140 can include a porous polymer film (porous polymer film) made from a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, ethylene/methacrylate copolymer. The separator may include a nonwoven fabric (nonwoven fabric) made of glass fibers, polyethylene terephthalate fibers, or the like having a high melting point.
The separator 140 may extend between the positive electrode 100 and the negative electrode 130, and may be folded (folded) and wound (wound) in the thickness direction of the lithium secondary battery. Accordingly, the plurality of positive electrodes 100 and negative electrodes 130 may be stacked in the thickness direction with the separator 140 interposed therebetween (laminated).
In some embodiments, an electrode cell (electrode cell) is defined by the positive electrode 100, the negative electrode 130, and the separator 140, and a plurality of electrode cells are stacked to form, for example, a jelly roll type electrode assembly 150. For example, the electrode assembly 150 may be formed by winding (winding), laminating (lamination), folding (folding), or the like of the separator 140.
The electrode assembly 150 is enclosed in the case 160, and an electrolyte may be injected together into the case 160. The housing 160 may comprise, for example, a soft pack shape, a pot shape, or the like.
In some embodiments, a nonaqueous electrolyte may be used as the electrolyte.
The nonaqueous electrolytic solution may include a lithium salt of an electrolyte and an organic solvent. The lithium salt may be represented by Li +X-, for example, and as the anion of the lithium salt X - may be exemplified F-、Cl-、Br-、I-、NO3 -、N(CN)2 -、BF4 -、ClO4 -、PF6 -、(CF3)2PF4 -、(CF3)3PF3 -、(CF3)4PF2 -、(CF3)5PF-、(CF3)6P-、CF3SO3 -、CF3CF2SO3 -、(CF3SO2)2N-、(FSO2)2N-、CF3CF2(CF3)2CO-、(CF3SO2)2CH-、(SF5)3C-、(CF3SO2)3C-、CF3(CF2)7SO3 -、CF3CO2 -、CH3CO2 -、SCN- and (CF 3CF2SO2)2N-, etc.
As the organic solvent, for example, propylene Carbonate (PC), ethylene Carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide (DMSO), acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane (sulfolane), γ -butyrolactone, propylene sulfite, tetrahydrofuran, and/or the like can be used. These may be used alone or in combination of two or more thereof.
In some embodiments, the solubility of the lithium salt-containing coating in the electrolyte may be 1g/L or less, preferably 0.1g/L or less. For example, the lithium salt-containing coating layer may have the low solubility described above in an organic solvent contained in the electrolyte.
Therefore, the lithium salt-containing coating layer can have improved chemical stability and low reactivity to the electrolyte, so that deterioration of the electrode active material layer by the electrolyte can be suppressed. Accordingly, it is possible to provide a lithium secondary battery having improved capacity retention (capacity retention rate) and high efficiency even during repeated charge/discharge behaviors.
As shown in fig. 3, tabs (positive and negative tabs) may protrude from the positive and negative current collectors 105 and 125, respectively, belonging to each electrode unit, and may extend to one side of the case 160. The electrode tab may be fused with one side of the case 160 to form electrode leads (the positive electrode lead 107 and the negative electrode lead 127) extending or exposed to the outside of the case 160.
Fig. 3 illustrates that the positive electrode lead 107 and the negative electrode lead 127 are formed at the same side of the lithium secondary battery or the can 160, but the electrode leads may be formed at opposite sides to each other.
For example, the positive electrode lead 107 may be formed at one side of the case 160, and the negative electrode lead 127 may be formed at the other side of the case 160.
The lithium secondary battery may be manufactured, for example, in a cylindrical shape (using a can), a prismatic shape (square shape), a soft pack shape (pouch type), or a coin shape (coin shape).
In the following, experimental examples including specific examples and comparative examples are presented in order to facilitate understanding of the present invention. However, the following examples are for illustrative purposes only and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the invention. Such changes and modifications are properly covered by the appended claims.
Examples and comparative examples
(1) Preparation of negative electrode active material including lithium salt-containing coating layer
100G of artificial graphite (D50:10 μm) was prepared as a negative electrode active material.
Thereafter, a process of forming a coating layer containing a lithium salt is performed. Specifically, a coating solution (coating solution) in which 5% by weight of lithium benzoate (C 7H5LiO2) was dissolved in a mixed solvent of water and ethanol was placed in a vacuum planetary mixer (vacuum planetary mixer) (KURABO mixer) manufactured by KURABO corporation), and the prepared negative electrode active material was added, followed by stirring at a stirring speed of 20Hz for 2 hours. The mixture was then dried under vacuum at a temperature of 60 ℃ for 24 hours to form a lithium salt-containing coating having a thickness as shown in table 1 below.
In table 1 below, "O" represents a negative electrode active material in which a coating layer containing a lithium salt is formed. "X" represents a negative electrode active material in which a coating layer containing a lithium salt is not formed. A negative electrode active material in which a lithium salt-containing coating layer is not formed is prepared in the same manner, except that a process of forming a lithium salt-containing coating layer is omitted.
(2) Preparation of anode active material layer including lithium salt-containing coating layer and secondary battery
The negative electrode active material, conductive material (carbon black), binder (SBR) and thickener (CMC) were prepared by mixing 94:3:1.5:1.2 to prepare a composition for a negative electrode. The prepared composition for a negative electrode was coated on a Cu foil, dried and rolled (roll) to prepare a negative electrode active material layer having a loading amount (loading amountof) of 10mg/cm 2 and a slurry density of 1.7 g/cc.
Thereafter, a process of forming a coating layer containing a lithium salt is performed. Specifically, a coating solution in which 5wt% of lithium benzoate (C 7H5LiO2) was dissolved in a mixed solvent of water and ethanol was applied on the anode active material layer, and then dried in a hot air furnace (concentration oven) at a temperature of 60 ℃ for 24 hours to form a lithium salt-containing coating layer having a thickness as shown in table 1 below.
A coin cell type secondary battery was manufactured using a Li foil as a counter electrode (counter electrode) and an electrolyte containing 1M LiPF 6 in a mixed solvent of EC and EMC (EC: emc=3:7).
In table 1 below, "O" represents a negative electrode active material layer in which a coating layer containing a lithium salt is formed. "X" represents a negative electrode active material layer in which a lithium salt-containing coating layer is not formed. The anode active material layer in which the lithium salt-containing coating layer is not formed is prepared in the same manner, except that the process of forming the lithium salt-containing coating layer is omitted.
(3) Measurement of arithmetic average (Ra) of surface roughness of negative electrode
Any of 50 or more regions of the upper surface of the produced negative electrode was designated, and the roughness (i.e., center line average roughness) of each region was measured 15 times using an atomic force microscope (Icon, bruker co.) under the condition that the XY scanning range was 0.5 μm×0.5 μm. The surface roughness value of each region is calculated as an arithmetic average excluding the maximum value and the minimum value among the measured values.
Thereafter, the Ra value of the negative electrode is calculated as an arithmetic average of the surface roughness values of each region.
Fig. 5 is a graph showing the distribution of the surface roughness values measured on the anode according to example 4 and comparative example 1.
Referring to fig. 5, the negative electrode of example 4 has a low arithmetic average of surface roughness values measured from the whole thereof, and a relatively narrow distribution. Accordingly, the negative electrode may have a surface roughness value of a low standard deviation value and a relatively constant roughness over the entire area of its surface.
However, the negative electrode according to comparative example 1 had a high arithmetic average value of the surface roughness values measured from the whole thereof, and a relatively wide distribution. Therefore, it was confirmed that the variation in roughness value was high for each region of the anode surface, and the roughness uniformity (uniformity) of the anode was low.
The standard deviation of the surface roughness value measured on the negative electrode according to example 4 was 2.3nm, and the standard deviation of the surface roughness value measured on the negative electrode according to comparative example 1 was 2.56nm.
(4) Measurement of the content (ppm) of a coating containing lithium salts
After charging (CC/CV 0.5c 4.2v 0.05c cut-off) and discharging (CC 0.5c 2.5v cut-off) the prepared secondary battery, 0.5g of a negative electrode active material sample was obtained from the negative electrode active material layer.
The obtained sample was added to 10g of deionized water (containing 0.1% trifluoroacetic acid (TFA)) and subjected to ultrasonic extraction for 20 minutes, and then the extracted solution was mixed for 12 hours and filtered through a syringe filter. The filtered samples were subjected to HPLC analysis under the following HPLC analysis conditions to measure the content of the lithium salt-containing coating.
< Conditions for HPLC analysis >
I) The device comprises: AGILENT HPLC 1200 module 1200
Ii) chromatography column: agilent C18,5 μm,150 x 4.6mm
Iii) Chromatographic column heater temperature: 30 DEG C
Iv) eluent: water (containing 0.1% trifluoroacetic acid): acetonitrile=9: 1
V) wavelength: 230nm
Vi) flow rate: 1.0 ml/min
Vii) sample injection volume: 30 μl
Viii) MS detector: thermo Scientific company, LTQ XL type
TABLE 1
Experimental example
(1) Evaluation of surface characteristics of the upper surface of the negative electrode
Fig. 6 is an Atomic Force Microscope (AFM) image showing the upper surface of the negative electrode according to example 4, and fig. 7 is an atomic force microscope image showing the upper surface of the negative electrode according to comparative example 1.
Referring to fig. 5 and 6, the negative electrode according to example 4 exhibited an arithmetic average roughness of 23nm or less, and the upper surface of the negative electrode was uniform (uniform).
Referring to fig. 7, the anode according to comparative example 1 showed that no coating layer containing lithium salt was formed on both the anode active material and the anode active material layer, and the upper surface of the anode was non-uniform.
(2) Evaluation of initial efficiency
The secondary batteries according to examples and comparative examples were charged (CC/CV 0.5c 4.2V 0.05c off) and discharged (CC 0.5c 2.5V off) to measure initial charge/discharge capacities (CC: constant Current, CV: constant Voltage). The initial efficiency was evaluated by dividing the initial discharge capacity by the percentage of the value of the initial charge capacity.
(3) Evaluation of Capacity Retention Rate
The charge (CC/CV method, current magnification 0.5C, upper limit voltage 4.2V, off current 0.05C) and discharge (CC, 0.5C, lower limit voltage 2.5V off) were set to one cycle at 25 ℃, in such a manner that 300 charge/discharge cycles were repeated for the secondary batteries according to the examples and comparative examples. Thereafter, the capacity retention was evaluated as a percentage of a value obtained by dividing the discharge capacity of 300 cycles by the discharge capacity of one cycle.
The evaluation results are shown in table 2 below.
TABLE 2
Referring to table 2, the secondary batteries of the examples including the lithium salt-containing coating layer exhibited an arithmetic average value of the surface roughness of the negative electrode of 25nm or less, and improved initial efficiency and capacity retention.
On the other hand, the secondary battery of comparative example 1, which did not include a lithium salt-containing coating layer, exhibited an arithmetic average value of the surface roughness of the negative electrode of more than 25nm, and the initial efficiency and capacity retention rate were lowered.
Further, the secondary batteries of comparative examples 2 and 3 exhibited high surface roughness values, and initial efficiency and cycle characteristics were lowered.
Meanwhile, the secondary batteries of examples 7 to 9 showed that the performance of the secondary batteries as a whole was improved due to the formation of the lithium salt-containing coating layer on the surface of the anode active material and the surface of the anode active material layer.
Claims (13)
1. An electrode for a lithium secondary battery, comprising:
An electrode current collector;
An electrode active material layer disposed on at least one surface of the electrode current collector and including electrode active material particles; and
A lithium salt-containing coating layer formed on at least a portion of the surface of the electrode active material particles and/or at least a portion of the surface of the electrode active material layer,
Wherein the electrode has an arithmetic average Ra of surface roughness represented by formula 1:
[ 1]
Ra≤25nm
Wherein, in formula 1, ra is a value obtained by calculating an arithmetic average of surface roughness values measured in 20 or more measurement regions of the electrode surface in a scanning range of 0.5 μm×0.5 μm using an atomic force microscope.
2. The electrode for a lithium secondary battery according to claim 1, wherein an arithmetic average Ra of the surface roughness is 0.1nm to 25nm.
3. The electrode for a lithium secondary battery according to claim 1, wherein the surface roughness value measured in each of the measurement regions is an arithmetic average of surface roughness values excluding a maximum value and a minimum value among roughness values measured 15 times or more for each of the measurement regions in a scanning range of 0.5 μm x 0.5 μm.
4. The electrode for a lithium secondary battery according to claim 1, wherein a standard deviation of a surface roughness value measured in a measurement area of the electrode surface is 2.5nm or less.
5. The electrode for a lithium secondary battery according to claim 1, wherein the lithium salt-containing coating layer has a continuous film shape, and the lithium salt-containing coating layer covers the surface of the electrode active material particles or the surface of the electrode active material layer.
6. The electrode for a lithium secondary battery according to claim 1, wherein the thickness of the lithium salt-containing coating layer is 1nm to 1000nm.
7. The electrode for a lithium secondary battery according to claim 1, wherein the coating layer containing a lithium salt comprises at least one of ：LiCl、LiF、Li3PO4、LiBO2、LiIO2、Li2CO3、Li2B4O7、Li2SO4、LiBr、LiI、LiNO3、Li(CF3CO2)、Li((CH3)3SiO)、Li(CH3O)、LiCH3COO、Li(CO2CH3)、 lithium isopropoxide ((CH 3)2 CHOLi), lithium lactate (CH 3CH(OH)COOLi)、Li2S、LiOH、Li2O、Li2O2), lithium ethoxide (CH 3CH2 OLi), lithium phenoxide (C 6H5 OLi) and/or lithium benzoate (C 7H5LiO2).
8. The electrode for a lithium secondary battery according to claim 1, wherein the content of the lithium salt-containing coating layer is 20ppm to 600ppm as measured by High Performance Liquid Chromatography (HPLC), based on the total weight of the electrode active material layer.
9. The electrode for a lithium secondary battery according to claim 1, wherein the coating layer containing a lithium salt is formed on both the surface of the electrode active material particles and the surface of the electrode active material layer.
10. The electrode for a lithium secondary battery according to claim 1, wherein the lithium ion conductivity of the lithium salt-containing coating layer is 1 x 10 -7 S/cm or more and the electron conductivity is 1 x 10 -5 S/cm or less.
11. The electrode for a lithium secondary battery according to claim 1, wherein the electrode is a negative electrode or a positive electrode.
12. A lithium secondary battery, comprising:
A positive electrode; and
A negative electrode disposed opposite to the positive electrode,
Wherein at least one of the positive electrode and the negative electrode is the electrode for a lithium secondary battery according to claim 1.
13. The lithium secondary battery according to claim 12, further comprising an electrolyte impregnating the positive electrode and the negative electrode,
Wherein the solubility of the lithium salt-containing coating in the electrolyte is 1g/L or less.
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| KR10-2022-0157578 | 2022-11-22 | ||
| KR1020230028636A KR20240076652A (en) | 2022-11-22 | 2023-03-03 | Electrode for lithium secondary battery and lithium secondary battery including the same |
| KR10-2023-0028636 | 2023-03-03 |
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| CN118073519A true CN118073519A (en) | 2024-05-24 |
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