CN113394391A - Nonaqueous electrolyte secondary battery - Google Patents

Nonaqueous electrolyte secondary battery Download PDF

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Publication number
CN113394391A
CN113394391A CN202110271060.7A CN202110271060A CN113394391A CN 113394391 A CN113394391 A CN 113394391A CN 202110271060 A CN202110271060 A CN 202110271060A CN 113394391 A CN113394391 A CN 113394391A
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positive electrode
negative electrode
capacity
secondary battery
electrolyte secondary
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三浦研
小野寺学史
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Seiko Instruments Inc
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Seiko Instruments Inc
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
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  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Secondary Cells (AREA)

Abstract

The invention aims to: provided is a nonaqueous electrolyte secondary battery having excellent heat resistance which can withstand heating such as reflow soldering. The nonaqueous electrolyte secondary battery of the present invention is characterized in that: the nonaqueous electrolyte secondary battery is characterized in that a positive electrode, a negative electrode, an electrolyte solution containing a supporting salt and a solvent, and a separator are contained in a container composed of a positive electrode can and a negative electrode can, wherein the positive electrode contains a spinel-type lithium manganese oxide as an active material, the negative electrode contains a carbon-coated SiOx as an active material, the electrolyte solution contains a mixed solvent containing Ethylene Carbonate (EC) and Vinylene Carbonate (VC) in an ethylene glycol dimethyl ether solvent, the separator contains glass fibers, and the ratio of the negative electrode capacity to the positive electrode capacity, that is, the value of (negative electrode capacity/positive electrode capacity) is in the range of 1.7 to 2.4.

Description

Nonaqueous electrolyte secondary battery
Technical Field
The present invention relates to a nonaqueous electrolyte secondary battery.
Background
The method uses silicon oxide (SiO) with carbon-coated surfacex) Patent document 1 below describes that excellent initial capacity and cycle characteristics can be obtained in the small nonaqueous electrolyte secondary battery of (1).
In recent years, in small nonaqueous electrolyte secondary batteries, reflow soldering has been required to be compatible with the battery in order to improve soldering efficiency when mounting a circuit board.
Conventionally, a structure capable of reflow soldering has been provided in a small nonaqueous electrolyte secondary battery including a combination of a positive electrode active material of lithium manganese oxide and a negative electrode active material of lithium aluminum alloy.
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open publication No. 2013-101770.
Disclosure of Invention
Problems to be solved by the invention
However, in order to make a secondary battery using the silicon oxide for the negative electrode compatible with the backflow instead of the combination of the active materials, it is considered that a member having high heat resistance is used, and in addition, it is necessary to suppress an unexpected reaction of the electrode or the electrolyte solution and stabilize charge and discharge.
In particular, although the battery capacity is considered to be decreased by heating during reflow soldering, it is desirable that the capacity retention rate, which is the ratio of the assembled capacity to the reflowed capacity, is large.
In view of the above problems, the present invention has an object to provide a small nonaqueous electrolyte secondary battery which is excellent in cycle characteristics and long-term storage stability and can be mounted by reflow.
Means for solving the problems
"1" in order to solve the above problem, a nonaqueous electrolyte secondary battery according to an embodiment of the present invention is characterized in that: the nonaqueous electrolyte secondary battery is obtained by storing a positive electrode, a negative electrode, an electrolyte solution containing a supporting salt (supporting electrolyte) and a solvent, and a separator (separator) in a storage container composed of a positive electrode can and a negative electrode can, wherein the positive electrode contains a spinel-type lithium manganese oxide as an active material, the negative electrode contains a carbon-coated SiOx as an active material, the electrolyte solution contains a mixed solvent containing ethylene carbonate (EC, ethylene carbonate) and Vinylene Carbonate (VC) in an ethylene glycol dimethyl ether solvent, the separator contains glass fibers, and the value of the ratio of the negative electrode capacity to the positive electrode capacity (negative electrode capacity/positive electrode capacity) is in the range of 1.7 to 2.4.
In this embodiment, an electrolyte composed of a mixed solvent containing ethylene carbonate and vinylene carbonate is combined with a combination of a positive electrode active material containing a spinel-type lithium manganese oxide and a negative electrode active material containing carbon-coated SiOx, and the value (negative electrode capacity/positive electrode capacity) is set to be in the range of 1.7 to 2.4. This structure can be adapted to reflow soldering, and can provide a small-sized nonaqueous electrolyte secondary battery having excellent capacity retention after heating accompanying reflow soldering, and also having excellent cycle characteristics and long-term storage stability.
"2" in the nonaqueous electrolyte secondary battery according to the above-mentioned one embodiment, the value of (negative electrode capacity/positive electrode capacity) is preferably in the range of 1.9 to 2.4.
In this embodiment, by setting the value of (negative electrode capacity/positive electrode capacity) to a range of 1.9 to 2.4, an excellent initial capacity can be obtained, and an excellent capacity retention rate can be obtained.
"3" in the nonaqueous electrolyte secondary battery according to the above-described one embodiment, characterized in that: the positive electrode can has a cylindrical shape with a bottom, the negative electrode can is fixed to the inside of an opening of the positive electrode can via a gasket, the container is sealed by providing a caulking portion for caulking the opening of the positive electrode can to the negative electrode can, and the positive electrode, the negative electrode, the separator, and the electrolyte are contained in the container.
In this aspect, a button-type nonaqueous electrolyte secondary battery having a sealed structure in which a caulking portion is provided in the negative electrode can and the positive electrode can via the gasket can be provided. In addition, the nonaqueous electrolyte secondary battery is less in capacity reduction after reflow soldering, and a button-type secondary battery having excellent initial capacity and excellent capacity retention rate can be provided.
Effects of the invention
According to this aspect, a small nonaqueous electrolyte secondary battery that can be adapted to reflow soldering and is excellent in cycle characteristics and long-term storage stability can be provided.
Drawings
Fig. 1 is a sectional view showing a nonaqueous electrolyte secondary battery according to embodiment 1.
Fig. 2 is a graph showing the relationship between the capacity retention rate and the capacity balance between the positive and negative electrodes in the case where a heat treatment corresponding to reflow soldering was applied to a plurality of nonaqueous electrolyte secondary batteries produced in examples.
Fig. 3 is a graph showing the relationship between the capacity of a plurality of nonaqueous electrolyte secondary batteries produced in examples and the capacity balance between the batteries after the batteries were exposed to a high-temperature and high-humidity environment of 60 ℃ and 90% RH for 20 days after heat treatment equivalent to reflow soldering.
Detailed Description
Hereinafter, an example of the nonaqueous electrolyte secondary battery according to the embodiment of the present invention will be described in detail with reference to fig. 1. The nonaqueous electrolyte secondary battery described in the present invention is a secondary battery in which an active material serving as a positive electrode or a negative electrode and a separator are contained in a container. In the drawings used for the following description, the scale of each member is appropriately changed and displayed so that each member can be recognized.
[ 1 st embodiment of nonaqueous electrolyte Secondary Battery ]
The nonaqueous electrolyte secondary battery 1 of the present embodiment shown in fig. 1 is a so-called coin (button) type battery. The nonaqueous electrolyte secondary battery 1 includes: a metallic positive electrode can 12 having a bottomed cylindrical shape, a metallic negative electrode can 22 having a covered cylindrical shape covering the opening of the positive electrode can 12, and a gasket 40 provided along the inner peripheral surface of the positive electrode can 12.
The nonaqueous electrolyte secondary battery 1 includes a thin (flat) container 2 in which a positive electrode can 12 is disposed outside a negative electrode can 22 via a gasket 40, and an inner peripheral edge of an opening of the positive electrode can 12 is caulked inside. A storage space surrounded by the positive electrode can 12 and the negative electrode can 22 is formed in the storage container 2, and the positive electrode 10 and the negative electrode 20 are arranged to face each other with the separator 30 interposed therebetween and further filled with the electrolyte 50.
As the material of the positive electrode can 12, conventionally known materials are used, and examples thereof include: stainless steel such as SUS316L or SUS329 JL.
The material of the negative electrode can 22 is, as with the material of the positive electrode can 12, conventionally known stainless steel, and examples thereof include: SUS316L, SUS329JL, or SUS304-BA, etc. In addition, a coating material obtained by laminating copper, nickel, or the like on stainless steel may be used for the negative electrode can. The outer diameter of the container 2 is about 4 to 12mm, for example.
(Positive electrode)
In this embodiment, the positive electrode 10 is electrically connected to the inner surface of the positive electrode can 12 (the upper surface of the bottom wall of the container 2 in fig. 1) via the positive electrode current collector 14, and the negative electrode 20 is electrically connected to the inner surface of the negative electrode can 22 (the lower surface of the top wall of the container 2 in fig. 1) via the negative electrode current collector 24. The positive electrode current collector 14 and the negative electrode current collector 24 may be omitted, and the positive electrode 10 may be directly connected to the positive electrode can 12 to provide the positive electrode can 12 with the function of a current collector, or the negative electrode 20 may be directly connected to the negative electrode can 22 to provide the negative electrode can 22 with the function of a current collector.
The spacer 40 is connected to the outer peripheral edge of the separator 30 inside the storage container 2, and the spacer 40 holds the separator 30. The positive electrode 10, the negative electrode 20, and the separator 30 are impregnated with the electrolyte 50 filled in the container 2.
In the positive electrode 10, the type of the positive electrode active material is not particularly limited, and for example, a material containing a spinel-type lithium manganese oxide is preferably used as the positive electrode active material.
The content of the positive electrode active material in the positive electrode 10 is determined in consideration of the discharge capacity required for the nonaqueous electrolyte secondary battery 1, and may be in the range of 50 to 95 mass%. If the content of the positive electrode active material is equal to or greater than the lower limit of the above preferable range, a sufficient discharge capacity is easily obtained, and if the content is equal to or less than the preferable upper limit, the positive electrode 10 is easily molded.
The positive electrode 10 may contain a conductive auxiliary agent (hereinafter, the conductive auxiliary agent used for the positive electrode 10 is sometimes referred to as "positive electrode conductive auxiliary agent").
Examples of the positive electrode conductive auxiliary agent include: carbon materials such as furnace black, ketjen black (Ketjenblack), acetylene black, and graphite.
The positive electrode conductive auxiliary agent may be used alone in 1 of the above, or may be used in combination with 2 or more.
The content of the positive electrode conductive additive in the positive electrode 10 is preferably 2to 20 mass%, and more preferably 4 to 15 mass%. When the content of the positive electrode conductive additive is not less than the lower limit of the above preferable range, sufficient conductivity can be easily obtained. In addition, when the electrode is formed into a pellet shape, the electrode can be easily formed. On the other hand, if the content of the positive electrode conductive additive in the positive electrode 10 is not more than the upper limit of the above preferable range, a sufficient discharge capacity based on the positive electrode 10 can be easily obtained.
The positive electrode 10 may contain a binder (hereinafter, the binder used for the positive electrode 10 is sometimes referred to as "positive electrode binder").
As the positive electrode binder, conventionally known ones can be used, and for example, Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), Styrene Butadiene Rubber (SBR), Polyacrylic Acid (PA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), or the like can be selected, and a binder composed of a combination of a plurality of these can be used.
In addition, the positive electrode binder can be used alone in 1, or can be combined with 2 or more. In the positive electrode 10, the content of the positive electrode binder may be set to 1 to 20 mass%, for example.
In the present specification, when "to" is used to indicate an upper limit and a lower limit with respect to a numerical range, the range includes the upper limit and the lower limit unless otherwise specified. Therefore, for example, when the content is 1 to 20% by mass, the content is 1% by mass or more and 20% by mass or less.
As the positive electrode current collector 14, a conventionally known current collector can be used, and an example thereof is a conductive resin binder using carbon as a conductive filler.
In the present embodiment, the positive electrode active material may contain, in addition to the lithium manganese oxide, other positive electrode active materials, for example, 1 or more kinds of other oxides such as molybdenum oxide, lithium iron phosphate compound, lithium cobalt oxide, lithium nickel oxide, and vanadium oxide.
(cathode)
In the negative electrode 20, the kind of the negative electrode active material is not particularly limited, and for example, silicon oxide is preferably contained as the negative electrode active material.
In the negative electrode 20, it is preferable that the negative electrode active material contains carbon-coated SiOxE.g. SiOx(0. ltoreq. x < 2) is carbon-coated with a silicon oxide.
In addition, the negative electrode 20 contains SiO as described abovex(0. ltoreq. x < 2) the negative electrode active material may contain other negative electrode active materials, for example, Si, C and the like.
In the use of granular SiOx(0. ltoreq. x < 2) as the negative electrode active material, the particle diameter (D50) is not particularly limited, and may be, for example, 0.1 to 30μm is in the range of 1 to 10, preferablyμm is in the range. If SiOxIf the particle diameter (D50) of (a) is less than the lower limit of the above range, for example, when the nonaqueous electrolyte secondary battery 1 is stored or used under a severe high-temperature and high-humidity environment, or the reactivity by the reflow soldering treatment is increased, which may deteriorate the battery characteristics, or if it exceeds the upper limit, the discharge rate may be decreased.
Negative electrode active material, i.e., SiO, in negative electrode 20x(0. ltoreq. x < 2) in consideration of the content of the nonaqueous electrolyte secondary batteryThe discharge capacity required for the cell 1 is determined, and a range of 50 mass% or more, preferably 60 to 80 mass% can be selected.
In the negative electrode 20, if the content of the negative electrode active material containing the above-described element is not less than the lower limit of the above range, a sufficient discharge capacity is easily obtained, and if the content is not more than the upper limit, the negative electrode 20 is easily molded.
The anode 20 may contain a conductive auxiliary (hereinafter, the conductive auxiliary used for the anode 20 is sometimes referred to as "anode conductive auxiliary"). The negative electrode conductive additive is the same as the positive electrode conductive additive.
The content of the negative electrode conductive additive in the negative electrode 20 is, for example, 1 to 45 mass%.
The anode 20 may contain a binder (hereinafter, the binder used for the anode 20 is sometimes referred to as "anode binder").
As the negative electrode binder, polyvinylidene fluoride (PVDF), Styrene Butadiene Rubber (SBR), Polyacrylic Acid (PA), carboxymethyl cellulose (CMC), Polyimide (PI), polyamide imide (PAI), or the like can be selected.
In addition, the negative electrode binder may be used alone of 1 kind, or may be used in combination of 2 or more kinds. When polyacrylic acid is used as the negative electrode binder, the polyacrylic acid may be adjusted to a pH of about 3 to 10. In this case, for example, an alkali metal hydroxide such as lithium hydroxide or an alkaline earth metal hydroxide such as magnesium hydroxide can be used for adjusting the pH.
The content of the negative electrode binder in the negative electrode 20 is, for example, in the range of 1 to 20 mass%.
In the present embodiment, the size and thickness of the negative electrode 20 can be formed in the same manner as those of the positive electrode 10.
Although not shown in the drawings, the nonaqueous electrolyte secondary battery 1 shown in fig. 1 may be configured such that a lithium body 60 such as a lithium foil is provided on the surface of the negative electrode 20, that is, between the negative electrode 20 and a separator 30 described later.
"electrolyte solution"
The electrolyte 50 is generally a liquid obtained by dissolving a supporting salt in a nonaqueous solvent.
In the nonaqueous electrolyte secondary battery 1 of this embodiment, the nonaqueous solvent forming the electrolytic solution 50 may use: a mixed solvent comprising tetraethylene glycol dimethyl ether (TEG) as a main solvent, Diethoxyethane (DEE) as a sub-solvent, and further comprising Ethylene Carbonate (EC) and Vinylene Carbonate (VC) as additives. The nonaqueous solvent is generally determined in consideration of heat resistance, viscosity, and the like required for the electrolytic solution 50, and in the present embodiment, a liquid containing each of the above solvents is used.
Examples of the main solvent used to form the glyme-based solvent include tetraglyme, triethylene glycol dimethyl ether, pentaethylene glycol dimethyl ether, and diethylene glycol dimethyl ether.
In this embodiment, the electrolytic solution 50 using a nonaqueous solvent containing tetraethylene glycol dimethyl ether (TEG), Diethoxyethane (DEE), and Ethylene Carbonate (EC) can be used. By adopting such a constitution, DEE and TEG form solvates with Li ions forming a supporting salt.
At this time, DEE selectively forms a solvate with Li ions because it has a higher donor number (donor number) than TEG. Thus, DEE and TEG form solvates with the Li ions forming the supporting salt, protecting the Li ions. This prevents the reaction between moisture and Li even when moisture enters the nonaqueous electrolyte secondary battery under a high-temperature and high-humidity environment, for example, and thus suppresses a decrease in discharge capacity and improves storage stability.
The ratio of each of the solvents in the nonaqueous solvent in the electrolytic solution 50 is not particularly limited, and for example, TEG: 30 to 48.5 mass% (30 to 48.5%), DEE: 30 to 48.5 mass% (30 to 48.5%), EC: 0.5 to 10 mass% (0.5 to 10%) and VC: a range of 2to 13 mass% (2 to 13%) inclusive (total 100%).
When the ratio of TEG to DEE to EC contained in the nonaqueous solvent is in the above range, the above-described effect of protecting Li ions by solvate formation of DEE and Li ions can be obtained.
Even in the above range, the content of VC is preferably in the range of 2.5 mass% or more and 10 mass% or less (2.5 to 10%), more preferably in the range of 5.0 mass% or more and 7.5 mass% or less (5.0 to 7.5%). The upper limit of the content of TEG and DEE is preferably 48.25% by mass or less, and more preferably 48% by mass or less.
When the VC content is in the range of 2 mass% to 13 mass%, even if the container 2 including the positive electrode can 12 and the negative electrode can 22 is heated during reflow, the change in thickness is small, and the increase in internal resistance can be reduced. In addition, when the content of VC is in the range of 2.5 mass% or more and 10.0 mass% or less, even if the heat is applied during reflow soldering, the variation in thickness occurring in the housing container 2 can be further reduced, and the increase in internal resistance can be further reduced. Even within the above range, the content of VC is most preferably in the range of 5.0 mass% or more and 7.5 mass% or less.
As the supporting salt, known Li compounds used as supporting salts for electrolytic solutions of nonaqueous electrolyte secondary batteries can be used, and for example: LiCH3SO3、LiCF3SO3、LiN(CF3SO2)2、LiN(C2F5SO2)2、LiC(CF3SO2)3、LiN(CF3SO3)2、LiN(FSO2)2And organic acid lithium salts; LiPF6、LiBF4、LiB(C6H5)4And lithium salts such as lithium salts of inorganic acids such as LiCl and LiBr. Among them, lithium salts as compounds having lithium ion conductivity are preferable, and LiN (CF) is more preferable3SO2)2、LiN(FSO2)2、LiBF4LiN (CF) is particularly preferred from the viewpoint that it has low heat resistance and reactivity with moisture and can sufficiently exhibit storage characteristics3SO2)2。
The supporting salt may be used alone in 1 of the above, or may be used in combination with 2 or more.
The content of the supporting salt in the electrolyte 50 is determined in consideration of the kind of the supporting salt, and is, for example, preferably 0.1 to 3.5mol/L, more preferably 0.5 to 3mol/L, and particularly preferably 1 to 2.5 mol/L. Even if the supporting salt concentration in the electrolyte 50 is too high or too low, the conductivity may be lowered, which may adversely affect the battery characteristics.
"(value of negative electrode Capacity/Positive electrode Capacity)"
In the nonaqueous electrolyte secondary battery 1 of this embodiment, the value of "(negative electrode capacity/positive electrode capacity) = positive-negative electrode capacity balance" is preferably in the range of 1.7 to 2.4.
If the value of (negative electrode capacity/positive electrode capacity) is less than 1.7, in other words, if the positive electrode capacity is greater, the capacity after assembly can be sufficiently obtained, but the capacity retention rate after reflow heating is reduced, and a sufficient battery capacity cannot be obtained after reflow heating.
On the other hand, if the value (negative electrode capacity/positive electrode capacity) exceeds 2.4, in other words, if the negative electrode capacity is larger, the capacity retention rate is a sufficiently high value, but the amount of positive electrode is relatively small, and a sufficient battery capacity cannot be obtained after assembly or after reflow.
Therefore, the value of (negative electrode capacity/positive electrode capacity) is preferably in the range of 1.7 to 2.4. When the value (negative electrode capacity/positive electrode capacity) is in the range of 1.7 to 2.4, the nonaqueous electrolyte secondary battery 1 having a large capacity retention rate after reflow heating and a large initial capacity can be provided.
The value (negative electrode capacity/positive electrode capacity) is more preferably in the range of 1.9 to 2.4. If the amount is within this range, a sufficiently high capacity can be obtained after assembly, and the capacity retention rate after reflow heating becomes larger, so that a higher battery capacity can be obtained after reflow heating.
Even within the above range, in order to ensure the initial capacity and to make the capacity retention rate after the reflow heating to be high, it is most preferable to set the range to 1.94 to 2.39.
The negative electrode capacity shown here is a capacity obtained by calculating the product of the capacity density of the active material in the negative electrode and the amount of the active material used. The positive electrode capacity is a capacity obtained by calculating the product of the capacity density of the active material and the amount of the active material used in the positive electrode. As the capacity density of the active material, 137mAh/g was used for lithium manganate and 1775mAh/g was used for silicon monoxide.
The capacity density of the active material is a value obtained by preparing an electrochemical cell in which a positive electrode or a negative electrode is opposed to Li metal, actually charging and discharging the cell, and estimating the respective capacity densities from the obtained cell capacities. As theoretical capacities, it is known that lithium manganate has a value of 148mAh/g and SiO has a value of 2007mAh/g, but the values described above are used in the present application.
The following is given (negative electrode capacity/positive electrode capacity): example of calculation of capacity balance.
The positive electrode mixture ratio is lithium manganese oxide: graphite: polyacrylic acid = 95: 4: 1 (mass ratio), and the positive electrode capacity was 2.14mAh because 16.4mg of the positive electrode material mixture (15.6 mg of lithium manganate) was used.
The negative electrode mixture ratio is silicon monoxide: graphite: polyacrylic acid = 75: 20: 5 (mass ratio), 3.1mg of the negative electrode mixture (2.3 mg of SiO) was used, and therefore the negative electrode capacity was 4.08 mAh.
The amount of Li is adjusted in combination with the amount of SiO (the ratio of the number of Li atoms to the number of SiO molecules is designed to be about 4: 1).
Capacity balance under the conditions described above: the examples of calculation of (negative electrode capacity/positive electrode capacity) and the examples of calculation of the designed Li amount are shown in tables 1 and 2 below.
[ Table 1]
Figure 462135DEST_PATH_IMAGE001
[ Table 2]
Figure 54921DEST_PATH_IMAGE002
(baffle)
The separator 30 is interposed between the positive electrode 10 and the negative electrode 20, and uses an insulating film having a large ion permeability and mechanical strength.
As the separator 30, those conventionally used for separators of nonaqueous electrolyte secondary batteries can be applied without any limitation, and examples thereof include: and nonwoven fabrics made of resins such as alkali glass, borosilicate glass, quartz glass, lead glass, polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyethylene terephthalate (PET), polyamide imide (PAI), polyamide, and Polyimide (PI). Among them, a glass nonwoven fabric is preferable, and a borosilicate glass nonwoven fabric is more preferable. The glass nonwoven fabric has excellent mechanical strength and large ion permeability, so that the internal resistance can be reduced to improve the discharge capacity.
The thickness of the separator 30 is determined in consideration of the size of the nonaqueous electrolyte secondary battery 1, the material of the separator 30, and the like, and may be, for example, 5 to 300μm。
(pad)
The gasket 40 is preferably made of a resin having a heat distortion temperature of 230 ℃ or higher, for example. If the heat distortion temperature of the resin material used for the gasket 40 is 230 ℃ or higher, the gasket can be prevented from being deformed significantly by heating in the reflow process or in the use of the nonaqueous electrolyte secondary battery 1, and leakage of the electrolytic solution 50 can be prevented.
As shown in fig. 1, the gasket 40 is formed in an annular shape along the inner peripheral surface of the positive electrode can 12, and the outer peripheral end 22a of the negative electrode can 22 is disposed inside the annular groove 41.
The gasket 40 has an annular outer edge portion 40A having an outer diameter and inserted without a gap into the inner peripheral side of the opening of the positive electrode can 12. The gasket 40 has an annular inner edge portion 40B having an outer diameter and inserted into the inner peripheral edge of the negative electrode can 22 without a gap. The gasket 40 has a bottom wall portion 40C connecting lower end portions of the outer edge portion 40A and the inner edge portion 40B.
Therefore, an annular groove 41 into which the outer peripheral end 22a of the negative electrode can 22 is inserted is formed on the outer peripheral upper surface side of the gasket 40.
By caulking the peripheral edge portion 12b of the opening 12a of the positive electrode can 12 shown in fig. 1 to the inside, that is, the negative electrode can 22 side, the gasket 40 can be sandwiched together with the negative electrode can 22, and the storage container 2 having a structure in which the storage space is sealed is configured.
As the material of the spacer 40, for example, there can be mentioned: polyphenylene Sulfide (PPS), polyethylene terephthalate (PET), polyamide, Liquid Crystal Polymer (LCP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA), polyether ether ketone resin (PEEK), polyether nitrile resin (PEN), polyether ketone resin (PEK), polyarylate resin, polybutylene terephthalate resin (PBT), polycyclohexanedimethylene terephthalate resin, polyether sulfone resin (PES), polyaminobismaleimide resin, polyetherimide resin, fluorine resin, and the like. In addition, a material obtained by adding glass fiber, mica whisker, ceramic fine powder, or the like to these materials in an amount of 30 mass% or less can be suitably used. By using such a material, the gasket can be prevented from being significantly deformed by heating, and the electrolyte 50 can be prevented from leaking.
According to the nonaqueous electrolyte secondary battery 1 of the present embodiment described above, since the electrolytic solution 50 in which the nonaqueous solvent mainly contains tetraethylene glycol dimethyl ether (TEG) and Diethoxyethane (DEE) and contains Ethylene Carbonate (EC) and the above-described Vinylene Carbonate (VC) in an appropriate amount range is provided, it is possible to provide a configuration that has heat resistance capable of withstanding reflow soldering, is less likely to cause vaporization of the solvent even when heated by reflow soldering, is less likely to cause an increase in the internal pressure of the storage container 2, and is less likely to cause deformation of the storage container 2.
Further, if the solvent is an ethylene glycol dimethyl ether solvent mainly containing tetraethylene glycol dimethyl ether and diethoxyethane, the boiling point of these solvents is high, and therefore the heat resistance of the electrolyte can be improved.
In addition, according to the nonaqueous electrolyte secondary battery 1 of the present embodiment, in addition to the combination of the positive electrode, the negative electrode, and the electrolyte solution, the value of (negative electrode capacity/positive electrode capacity) is set to be in the range of 1.7 to 2.4, so that the capacity retention rate after the reflow heating can be increased while securing a high capacity after the assembly, and a sufficient battery capacity can be obtained after the reflow heating. Therefore, according to the present embodiment, a high-capacity nonaqueous electrolyte secondary battery suitable for reflow soldering can be provided.
Examples
The nonaqueous electrolyte secondary battery having the structure shown in fig. 1 was subjected to an evaluation test described later.
As the positive electrode 10, commercially available lithium manganese oxide (Li)1.14Co0.06Mn1.80O4) Wherein graphite used as a conductive auxiliary agent and polyacrylic acid used as a binder are selected from lithium manganese oxide: graphite: polyacrylic acid = 95: 4: 1 (mass ratio) to form a positive electrode mixture. At a rate of 2ton/cm216.4mg of the positive electrode mixture was pressurized and pressure-molded into disk-shaped pellets having a diameter of 2.8 mm.
The obtained particles (positive electrode) were bonded to the inner surface of a positive electrode can made of stainless steel (SUS 316L: t =0.20mm) using a conductive resin binder containing carbon, and they were integrated to obtain a positive electrode unit. Then, the positive electrode cell was dried by heating under reduced pressure at 120 ℃ for 11 hours in the air. Next, a sealing agent is applied to the inner surface of the opening of the positive electrode can in the positive electrode unit.
Next, as a negative electrode, SiO powder having carbon (C) formed on the entire surface thereof was prepared, and this was used as a negative electrode active material. Then, in the negative electrode active material, graphite as a conductive agent and polyacrylic acid as a binder were mixed in a ratio of 75: 20: 5 (mass ratio) to form a negative electrode mixture. At a rate of 2ton/cm23.1mg of the negative electrode mixture was press-molded into disc-shaped pellets having a diameter of 2.8 mm.
The obtained particles (negative electrode) were bonded to the inner surface of a negative electrode can made of stainless steel (SUS 316L: t =0.20mm) using a conductive resin binder using carbon as a conductive filler, and they were integrated to obtain a negative electrode unit. Then, the negative electrode cell was dried by heating under reduced pressure at 160 ℃ for 11 hours in the air.
This pellet-shaped negative electrode was further pressed and punched into a lithium foil having a diameter of 2.8mm and a thickness of 0.44mm to obtain a lithium-negative electrode laminated electrode.
As described above, in this example, the positive electrode can was made to function as the positive electrode collector and the negative electrode can were made to function as the negative electrode collector, without providing the positive electrode collector and the negative electrode collector as described in the configuration of the embodiment, thereby producing a nonaqueous electrolyte secondary battery.
Subsequently, the nonwoven fabric made of glass fibers was dried and then punched into a disk shape having a diameter of 3.6mm to form a separator. Then, the separator was placed on a lithium foil laminated on the negative electrode, and a gasket made of PEEK resin (polyether ether ketone resin) was disposed in the opening of the negative electrode can.
(preparation of electrolyte solution)
Tetraglyme (TEG), Diethoxyethane (DEE), Ethylene Carbonate (EC), and Vinylene Carbonate (VC) were mixed to form a nonaqueous solvent, and LiTFSI (1M) as a supporting salt was dissolved in the obtained nonaqueous solvent to obtain an electrolytic solution. At this time, the mixing ratio of each solvent was TEG: DEE: EC: VC = 44.8: 42.7: 5.0: 7.5.
the positive electrode can and the negative electrode can prepared as described above were filled with the electrolyte solutions of the respective examples adjusted by the above procedure, and the total of each battery was 7μL。
Next, the negative electrode unit is riveted to the positive electrode unit so that the separator is in contact with the positive electrode. Then, the positive electrode can and the negative electrode can were sealed by fitting the opening of the positive electrode can, and then allowed to stand at 25 ℃ for 7 days to obtain a sample.
In the case of preparing samples, the amounts of the positive electrode active material in the positive electrode and the negative electrode active material in the negative electrode were adjusted in the same manner as in the above-described calculation example of "(negative electrode capacity)/(positive electrode capacity)", and the nonaqueous electrolyte secondary batteries of samples 1 to 9 having different values of (negative electrode capacity/positive electrode capacity) were obtained. The nonaqueous electrolyte secondary batteries of these samples were all coin-type secondary batteries having an outer diameter of 4.8mm and a height of 2.1 mm.
As shown in table 3 described later, the nonaqueous electrolyte secondary batteries of samples 1 to 9 are secondary batteries having different values of (negative electrode capacity/positive electrode capacity).
Evaluation test "
(initial Capacity: mAh)
After each sample of the nonaqueous electrolyte secondary battery was produced, the capacity was measured before heating to the temperature of reflow soldering. The capacity measured in this case was taken as the initial capacity.
(Capacity maintenance ratio)
Each sample of the nonaqueous electrolyte secondary battery was heated at 260 ℃ for 10 seconds, the capacity after heating was measured, and the capacity maintenance ratio (%) was determined by comparing with the initial capacity. The heating treatment at 260 ℃ for 10 seconds corresponds to the heating condition accompanying reflow soldering.
(Capacity after storage in high temperature and high humidity Environment)
Each sample of the nonaqueous electrolyte secondary battery was heated at 260 ℃ for 10 seconds, and the capacity after exposure to a high-temperature high-humidity environment of 60 ℃ and 90% RH and standing for 20 days was measured using a constant temperature and humidity tester. The capacity measured in this case was taken as the capacity after storage at high temperature and high humidity.
(results)
With respect to the nonaqueous electrolyte secondary batteries of samples 1 to 9, the value of "(negative electrode capacity/positive electrode capacity) = (positive-negative electrode capacity balance)", the value of initial capacity, the value of capacity retention rate after reflow, and the value of capacity after high-temperature and high-humidity storage are shown in table 3. Fig. 2 shows the relationship between the capacity retention rate and the initial capacity and the balance between the positive and negative electrode capacities, and fig. 3 shows the relationship between the capacity after storage at high temperature and high humidity and the balance between the positive and negative electrode capacities in the form of a graph.
[ Table 3]
Figure 450131DEST_PATH_IMAGE003
As seen from the measurement results shown in table 3 and fig. 2, when a good range (negative electrode capacity/positive electrode capacity) having a high initial capacity and a capacity retention rate after reflow exceeding 70% is selected, the range is 1.72 to 2.39. Thus, it can be seen that: in order to increase the initial capacity and to increase the capacity retention rate after reflow, it is desirable to select a range of 1.7 to 2.4 as the value of (negative electrode capacity/positive electrode capacity).
In addition, it is also known that: the initial capacity is higher than 1.97, and the capacity maintenance rate after reflow is more than 80%, and the more preferable range is that the value of (negative electrode capacity/positive electrode capacity) is in the range of 1.9 to 2.4.
Referring to the relationship between the capacity after high-temperature and high-humidity storage and the balance between the positive and negative electrode capacities shown in table 3 as shown in fig. 3, the capacity after high-temperature and high-humidity storage after long-term storage is high, and thus it can be said that: a preferable range is a range in which the value (negative electrode capacity/positive electrode capacity) is 1.7 or more, and a more preferable range is a range in which the value (negative electrode capacity/positive electrode capacity) is 1.9 to 2.4.
Description of the symbols
1: a nonaqueous electrolyte secondary battery; 2: a storage container; 10: a positive electrode; 12: a positive electrode can; 12 a: an opening part; 12 b: a peripheral edge portion; 13: a positive electrode; 14: a positive electrode current collector; 20: a negative electrode; 22: a negative electrode can; 22 a: an outer peripheral end portion; 24: a negative electrode current collector; 30: a partition plate; 40: a gasket; 41: an annular groove; 50: and (3) an electrolyte.

Claims (3)

1. A nonaqueous electrolyte secondary battery, characterized in that: a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, an electrolyte solution containing a supporting salt and a solvent, and a separator accommodated in an accommodating container comprising a positive electrode can and a negative electrode can,
wherein the positive electrode contains a spinel-type lithium manganese oxide as an active material, the negative electrode contains a carbon-coated SiOx as an active material, the electrolyte solution contains a mixed solvent containing Ethylene Carbonate (EC) and Vinylene Carbonate (VC) in an ethylene glycol dimethyl ether solvent, and the separator contains glass fibers,
the ratio of the negative electrode capacity to the positive electrode capacity (negative electrode capacity/positive electrode capacity), i.e., the value, is in the range of 1.7 to 2.4.
2. The nonaqueous electrolyte secondary battery according to claim 1, characterized in that: the value of (negative electrode capacity/positive electrode capacity) is in the range of 1.9 to 2.4.
3. The nonaqueous electrolyte secondary battery according to claim 1 or 2, characterized in that:
the positive electrode can has a cylindrical shape with a bottom,
the negative electrode can is fixed to the inside of the opening of the positive electrode can via a gasket,
the storage container is sealed by providing a caulking portion for caulking an opening portion of the positive electrode can to the negative electrode can side, and the positive electrode, the negative electrode, the separator, and the electrolyte are stored in the storage container.
CN202110271060.7A 2020-03-13 2021-03-12 Nonaqueous electrolyte secondary battery Pending CN113394391A (en)

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