JP2018190504A - Method for manufacturing nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a battery, which can suppress entry of dimethoxyethane into a negative electrode when nonaqueous electrolyte solution containing dimethoxyethane is used and a reduction in battery capacity.SOLUTION: A method for manufacturing a nonaqueous electrolyte secondary battery including a negative electrode and nonaqueous electrolyte solution comprises: a battery preparation step of preparing an uncharged nonaqueous electrolyte secondary battery; and an initial charging step of charging the uncharged nonaqueous electrolyte secondary battery, which has been prepared in the battery preparation step, plural times successively at least in a range of 2.5-2.9 V until reaching an intended voltage with a constant current and a constant voltage at a predetermined current rate, in which the battery is charged by a predetermined voltage at a time. The negative electrode comprises a negative electrode mixture layer including graphite. The nonaqueous electrolyte solution contains: dimethoxyethane of 20 vol.% or more; and 1,3-propane sultone of 0.1 mol/L or more and 0.6 mol/L or less.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a method for manufacturing a non-aqueous electrolyte secondary battery.

  As a solvent for the non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery, generally, a cyclic carbonate such as ethylene carbonate (EC) having a high dielectric constant, ethyl methyl carbonate (EMC), dimethyl having a low viscosity, and the like. A chain carbonate such as carbonate (DMC) or diethyl carbonate (DEC) is mixed and used. The EC has a function of forming a SEI (Solid Electrolyte Interface) film on the negative electrode to stabilize charging and discharging.

  In Japanese Patent Laid-Open No. 2001-325988 (Patent Document 1), vinylene carbonate (VC) which is a film additive is used to form a good SEI film on a negative electrode. Patent Document 1 further includes at least a step of charging at a potential at which the solvent is not reductively decomposed in order to form a VC film on the negative electrode by reductively decomposing VC while preventing reductive decomposition of the solvent. It is disclosed that initial charging is performed by a charging process of stages or more. In this specification, “initial charge” refers to the first charge performed on an uncharged non-aqueous electrolyte secondary battery (hereinafter, the non-aqueous electrolyte secondary battery is also abbreviated as “battery”). means.

JP 2001-325988 A

  On the other hand, the use of dimethoxyethane (hereinafter also abbreviated as “DME”) as a solvent for non-aqueous electrolytes has been studied. Since DME has a low viscosity, an improvement in the electrical conductivity of the non-aqueous electrolyte is expected. However, it is known that DME is co-inserted into the negative electrode and causes interlaminar fracture of graphite, which is the negative electrode active material. In the battery disclosed in Patent Document 1, when DME is used as the solvent for the non-aqueous electrolyte, there is a concern that the battery capacity is reduced due to the interlayer breakdown of graphite. Furthermore, battery resistance may increase due to graphite interlaminar fracture.

  The objective of this indication is in suppressing the fall of battery capacity in the manufacturing method of the battery using the non-aqueous electrolyte containing DME.

  Hereinafter, the technical configuration and operation mechanism of the present disclosure will be described. However, the mechanism of action of the present disclosure includes estimation. The scope of the present disclosure should not be limited by the correctness of the mechanism of action.

  A battery manufacturing method according to the present disclosure is a manufacturing method of a non-aqueous electrolyte secondary battery including a negative electrode and a non-aqueous electrolyte, and a battery preparation step of preparing an uncharged non-aqueous electrolyte secondary battery; For a non-charged non-aqueous electrolyte secondary battery, a constant current is continuously applied several times at a predetermined current rate in a predetermined voltage increment until a target voltage is reached in a range of at least 2.5 V to 2.9 V. An initial charging step of performing constant voltage charging. The negative electrode includes a negative electrode mixture layer containing graphite, and the non-aqueous electrolyte includes 20% by volume or more of dimethoxyethane and 0.1 to 0.6 mol / L of 1,3-propane sultone. . “C” is a unit of current rate. “1C” indicates a current rate at which SOC (State of Charge) reaches 0% to 100% by charging for one hour.

  The co-insertion potential of DME contained in the non-aqueous electrolyte and the reduction potential of 1,3-propane sultone (hereinafter also abbreviated as “PS”) have close numerical values. In this specification, “DME co-insertion potential” means a potential at which DME is co-inserted into the graphite contained in the negative electrode composite layer together with the supporting salt, and “PS reduction potential” means PS Means the potential at which reductive decomposition occurs. In the initial charging, constant current and constant voltage charging (hereinafter, constant current and constant voltage charging is performed in a range of 2.5 V to 2.9 V at a predetermined current rate at a predetermined current rate for a plurality of times until a target voltage is reached. , Which is also abbreviated as “CCCV charging”), co-insertion of DME into graphite and reductive decomposition of PS occur almost simultaneously, and a low-resistance mixed coating composed of DME and reductively decomposed PS is formed on the negative electrode. It is thought that it is formed. It is considered that the mixed coating suppresses co-insertion of DME into graphite. In order to efficiently form the coating film, the nonaqueous electrolytic solution contains 20% by volume or more of DME and 0.1 mol / L or more and 0.6 mol / L or less of PS. Furthermore, by repeating step charging and step discharging, at least a part of DME co-inserted into the graphite contained in the negative electrode mixture layer is desorbed from the graphite, and the DME co-inserted into the graphite is It is considered that the insertion into the inside can be suppressed. In this specification, “step charging” means a method of performing CCCV charging at a predetermined current rate at a predetermined voltage step, and “step discharging” is a constant current at a predetermined current rate at a predetermined voltage step. It means a method of performing constant voltage discharge (hereinafter, constant current constant voltage discharge is also abbreviated as “CCCV discharge”). The synergistic effect of these effects is expected to suppress a decrease in battery capacity. That is, when a non-aqueous electrolyte containing DME is used, a battery manufacturing method is provided in which co-insertion of DME into the negative electrode is suppressed and a decrease in battery capacity is suppressed.

It is a figure which shows the relationship between CC electric current value and battery voltage value in the initial stage charge process of Examples 1, 3 and Comparative Example 4. It is a figure which shows the relationship between CC electric current value and battery voltage value in the initial stage charge process of Example 2. FIG. It is a figure which shows the relationship between CC current value and a battery voltage value in the initial stage charge process of the comparative examples 1 and 2. It is a figure which shows the relationship between CC electric current value and battery voltage value in the initial stage charge process of the comparative example 3. It is a figure which shows the relationship between CC current value and a battery voltage value in the initial stage charge process of the comparative example 5.

  Hereinafter, an embodiment of the present disclosure (hereinafter referred to as “the present embodiment”) will be described. However, the following description does not limit the scope of the claims.

<Configuration of non-aqueous electrolyte secondary battery>
The non-aqueous electrolyte secondary battery of the present disclosure can have a conventionally known configuration as long as it includes a negative electrode and a non-aqueous electrolyte described below. The conventionally known configuration includes, for example, an electrode group having a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and the electrode group is disposed in a battery case together with a non-aqueous electrolyte. Say. An electrode group can be made into the form (winding electrode group) wound flatly.

<Method for producing non-aqueous electrolyte secondary battery>
A method for producing a non-aqueous electrolyte secondary battery according to the present disclosure includes an uncharged non-aqueous electrolyte secondary battery, a battery preparation step, and an uncharged non-aqueous electrolyte prepared in the battery preparation step. Initial charging for secondary battery with constant current and constant voltage charging continuously at a predetermined current rate at a predetermined voltage step multiple times at a predetermined voltage increment in a range of at least 2.5V to 2.9V. Process. As long as these steps are included, other steps can be included. In addition, the above two steps may further include sub-steps.

<Negative electrode>
The negative electrode includes a negative electrode current collector and a negative electrode mixture layer formed on the main surface of the negative electrode current collector. The negative electrode current collector may be, for example, a copper (Cu) foil. The negative electrode current collector may have a thickness of about 5 to 20 μm, for example.

<Negative electrode mixture layer>
The negative electrode mixture layer includes a negative electrode active material and a binder. The negative electrode mixture layer may include, for example, 95 to 99% by mass of a negative electrode active material and 1 to 5% by mass of a binder. The negative electrode mixture layer may have a thickness of about 50 to 150 μm, for example.

(Negative electrode active material and binder)
The negative electrode active material contains at least graphite. That is, the negative electrode of the present disclosure includes a negative electrode mixture layer containing graphite. As the graphite, natural graphite such as massive graphite and flake graphite, artificial graphite obtained by firing a carbon precursor, or those obtained by subjecting these graphite to processing such as pulverization, sieving, and pressing are used. be able to. Further, the graphite may be coated with amorphous carbon. The negative electrode active material may contain an active material other than graphite, and may further contain, for example, silicon, silicon oxide, tin, tin oxide and the like. The binder should not be particularly limited. The binder may be, for example, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), or the like.

<Non-aqueous electrolyte>
The nonaqueous electrolytic solution includes a nonaqueous solvent, an additive, and a supporting salt. The non-aqueous solvent contains at least DME, and the additive contains at least PS. The non-aqueous electrolyte may contain only DME as a non-aqueous solvent, or may contain other non-aqueous solvents in addition to DME. As other non-aqueous solvents, for example, cyclic or chain carbonates such as EC, EMC, DMC, and DEC may be used. The non-aqueous electrolyte may contain only PS as an additive, or may contain other additives in addition to PS. As other additives, for example, VC, cyclohexylbenzene (CHB) or the like may be used. The supporting salt may be a Li salt such as lithium hexafluorophosphate (LiPF ₆ ) or lithium tetrafluoroborate (LiBF ₄ ). The concentration of the Li salt may be, for example, about 0.5 to 2.0 mol / L.

  The nonaqueous electrolytic solution contains at least 20% by volume or more of DME with respect to the total amount in the nonaqueous electrolytic solution. When the content of DME contained in the non-aqueous electrolyte is less than 20% by volume, the electrical conductivity of the non-aqueous electrolyte may not be improved. The upper limit of the content of DME contained in the non-aqueous electrolyte is not particularly limited, but the DME is prevented from being co-inserted into the graphite with an increase in the content of DME contained in the non-aqueous electrolyte. May become difficult and battery capacity may be reduced. Therefore, the upper limit of the content of DME contained in the non-aqueous electrolyte may be, for example, 80% by volume or less, or 70% by volume or less with respect to the total amount in the non-aqueous electrolyte. 60 volume% or less, 50 volume% or less, 40 volume% or less, or 30 volume% or less may be sufficient.

  The non-aqueous electrolyte contains PS having a concentration of 0.1 mol / L or more and 0.6 mol / L or less. That is, the nonaqueous electrolytic solution of the present disclosure contains 20% by volume or more of DME and 0.1 to 0.6 mol / L of PS. When the concentration of PS in the non-aqueous electrolyte is less than 0.1 mol / L, the absolute amount of PS contained in the non-aqueous electrolyte is small, and it tends to be difficult to create a mixed film composed of DME and PS. There is. When the concentration of PS in the non-aqueous electrolyte exceeds 0.6 mol / L, the amount of DME contained in the non-aqueous electrolyte may be less than 20% by volume.

<Positive electrode>
The positive electrode includes a positive electrode current collector and a positive electrode mixture layer formed on the main surface of the positive electrode current collector. The positive electrode current collector may be, for example, an aluminum (Al) foil. The positive electrode current collector may have a thickness of 10 to 30 μm, for example.

<< Positive electrode mixture layer >>
The positive electrode mixture layer includes a positive electrode active material, a conductive material, and a binder. The positive electrode mixture layer may include, for example, 80 to 98% by weight of the positive electrode active material, 1 to 15% by weight or less of a conductive material, and 1 to 5% by weight or less of a binder. The positive electrode mixture layer may have a thickness of 100 to 200 μm, for example.

(Positive electrode active material, conductive material and binder)
The positive electrode active material, the conductive material, and the binder should not be particularly limited. The positive electrode active material may be, for example, LiCoO ₂ , LiNiO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM), LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ or the like. The conductive material may be, for example, acetylene black (AB), furnace black, vapor grown carbon fiber (VGCF), graphite or the like. The binder may be, for example, polyvinylidene fluoride (PVdF), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), or the like.

<Separator>
The separator is an electrically insulating porous film. The separator electrically isolates the positive electrode and the negative electrode. The separator may have a thickness of 5 to 30 μm, for example. The separator can be composed of, for example, a porous polyethylene (PE) film, a porous polypropylene (PP) film, or the like. The separator may include a multilayer structure. For example, the separator may be configured by laminating a porous PP film, a porous PE film, and a porous PP film in this order. The separator may include a heat resistant layer on the surface thereof. The heat resistant layer includes a heat resistant material. Examples of the heat resistant material include metal oxide particles such as alumina, and a high melting point resin such as polyimide.

<Electrode group>
The electrode body has a positive electrode, a negative electrode, and a separator provided between the positive electrode and the negative electrode. The electrode body may be, for example, a cylindrical electrode group.

<Battery case>
The battery case may be, for example, a rectangular shape (flat rectangular parallelepiped), a cylindrical shape, or a bag shape. For example, a metal such as aluminum (Al) or an Al alloy constitutes the battery case. However, as long as the battery case has a predetermined sealing property, for example, a composite material of metal and resin may constitute the battery case. Examples of the composite material of metal and resin include an aluminum laminate film. The battery case may include an external terminal, a liquid injection hole, a gas discharge valve, a current interruption mechanism (CID), and the like.

<Battery preparation process>
In the battery preparation process, an uncharged battery is prepared. The battery preparation step includes, for example, a step of preparing a positive electrode, a step of preparing a negative electrode, a step of preparing a separator, and a positive electrode, a separator, a negative electrode, and a separator so that the positive electrode and the negative electrode face each other with the separator interposed therebetween. A cylindrical electrode group, a step of housing the electrode group in a battery case, a step of injecting a non-aqueous electrolyte into the battery case, and a battery A step of sealing the case may be included.

<Initial charging process>
In the initial charging step, initial charging is performed on the uncharged battery prepared in the battery preparation step.

  In the initial charging process, CCCV charging (step charging) is continuously performed a plurality of times at a predetermined current rate at predetermined voltage increments until the battery voltage reaches a target voltage in a range of at least 2.5 V to 2.9 V. Is called. The “predetermined voltage increment” in this specification is desirably engraved with a voltage of 0.05 to 0.2 V, and the “predetermined current rate” is a current rate of 0.01 to 0.3 C. It is desirable. Step charging in the battery voltage range of 2.5V to 2.9V may be performed at least once. However, after the battery voltage reaches 2.9V in the initial charging step, step discharge is performed to reduce the battery voltage to 2.5V. Step charging may be performed again after being lowered. By performing step charging a plurality of times, the effect of detaching at least a part of DME co-inserted into the graphite contained in the negative electrode composite material layer from the graphite, and the DME co-inserted into the graphite are more inside the graphite. It is expected that the effect of suppressing insertion will be amplified.

  Initial charging is preferably performed at a reasonably low current rate. However, if the current rate is excessively low, the processing takes a long time, and the current rate of the initial charging is, for example, about 0.1 to 1.0C. Further, after the initial charging step, the battery may be aged by allowing the battery to stand at a predetermined temperature for a predetermined period.

  Hereinafter, examples of the present disclosure will be described. However, the following examples do not limit the scope of the claims.

<Manufacture of non-aqueous electrolyte secondary batteries>
Example 1
1. Production of positive electrode The following materials were prepared.
Cathode active material: NCM
Conductive material: AB
Binder: PVdF
Solvent: N-methyl-2pyrrolidone (NMP)
Positive electrode current collector foil: Al foil (thickness 15 μm)

  NCM, AB, PVdF and NMP were mixed by a planetary mixer. As a result, a paste-like positive electrode mixture (hereinafter referred to as “positive electrode mixture paste”) was prepared. The solid content composition of the positive electrode mixture paste was “NCM: AB: PVdF = 93: 4: 3” in terms of mass ratio. The paste for the positive electrode mixture layer was applied to the surface of the positive electrode current collector and dried. As a result, a positive electrode mixture layer was formed. From the above, a positive electrode for a nonaqueous electrolyte secondary battery was formed. The positive electrode was rolled and cut into strips.

2. Production of negative electrode The following materials were prepared.
Negative electrode active material: Amorphous coated natural graphite Thickener: CMC
Binder: SBR
Solvent: Water Negative electrode current collector foil: Cu foil (thickness 10 μm)
Here, the “amorphous coated natural graphite” in the present specification means a natural graphite that has been coated with amorphous carbon.

  By putting amorphous coated spheroidized natural graphite, CMC, SBR and water into the stirring tank of the stirring device and stirring, a paste-like negative electrode mixture (hereinafter referred to as “negative electrode mixture paste”) is obtained. Prepared. In the negative electrode composite paste, the solid content was “amorphous coated natural graphite: CMC: SBR = 98: 1: 1” in mass ratio. The negative electrode mixture layer paste was applied to the surface of the negative electrode current collector and dried. As a result, a negative electrode mixture layer was formed. Thus, a negative electrode for a non-aqueous electrolyte secondary battery was formed. The negative electrode was rolled and cut into strips.

3. Preparation of Nonaqueous Electrolytic Solution An electrolytic solution having the following composition was prepared.
Solvent composition: [EC: DMC: EMC: DME = 3: 1: 3: 3 (volume ratio)]
Supporting salt: LiPF ₆ (1.1 mol / L)
Additive: PS (0.28 mol / L)

4). Battery Preparation Step A strip-shaped positive electrode, a strip-shaped negative electrode, and a strip-shaped separator (polyethylene porous membrane) were prepared. The positive electrode, the separator, the negative electrode, and the separator were laminated in this order. Thus, an electrode group was configured. Furthermore, the positive electrode current collector plate, the electrode group, and the negative electrode current collector plate were laminated in this order, and terminals were connected to the positive electrode current collector plate and the negative electrode current collector plate, respectively. The electrode group was housed in a battery case made of a laminate film. A non-aqueous electrolyte was injected into the battery case, and the battery case was sealed. As described above, the battery was assembled and an uncharged battery was prepared.

5. Initial Charging Step An initial charging step was performed on an uncharged battery under the conditions shown in FIG. The conditions for the initial CCCV charging are as follows.
CC current: 0.1 C, CV voltage: 2.0 V, end current: 0.01 C.

  Step charging was performed on the battery charged to 2.0V until the battery voltage reached 3.0V. Similarly, the end current was set to 0.01C. In this step charging, the voltage was set to 0.1V and the current rate was set to 0.1C. The same applies to the following step charging.

CCCV charging was performed on the battery charged to 3.0 V by step charging. The conditions for CCCV charging are as follows.
CC current: 0.7 C, CV voltage: 4.1 V, end current: 0.01 C.

  Thus, a battery according to the present disclosure was obtained. The battery according to the present disclosure charged to 4.1 V was then aged at 60 ° C. for 1 day. Thus, a battery according to Example 1 shown in Table 1 was obtained. The battery has a laminate shape (width 60 mm, length 90 mm, thickness 2.5 mm). The battery is designed to have a capacity of 28 mAh in the voltage range of 3.0-4.1V.

<Example 2>
As described below, a battery was manufactured in the same manner as in Example 1 except that the initial charging step was performed under the conditions shown in FIG.

An initial CCCV charge was performed on the assembled uncharged battery. The conditions for the initial CCCV charging are as follows.
CC current: 0.1 C, CV voltage: 2.5 V, end current: 0.01 C.

  For the battery charged to 2.5V, the first step charge was performed until the battery voltage reached 2.9V.

  For the battery charged to 2.9V in the first step charge, the first step discharge was performed until the battery voltage became 2.5V. In the step discharge, the voltage was set to 0.1V and the current rate was set to 0.1C. The same applies to the following step discharge.

  For the battery discharged to 2.5V in the first step discharge, the second step charge was performed until the battery voltage became 2.9V.

  For the battery charged to 2.9V in the second step charge, the second step discharge was performed until the battery voltage reached 2.5V.

  For the battery discharged to 2.5V in the second step discharge, the third step charge was performed until the battery voltage became 2.9V.

CCCV charge was performed on the battery charged to 2.9 V in the third step charge. The conditions for CCCV charging are as follows.
CC current: 0.7 C, CV voltage: 4.1 V, end current: 0.01 C.

<Example 3>
As shown in Table 1 below, a battery was manufactured by the same manufacturing method as in Example 1 except that the concentration of PS contained in the nonaqueous electrolytic solution was changed.

<Comparative Example 1>
A battery was produced in the same manner as in Example 1 except that the additive was not used and the assembled uncharged battery was subjected to the initial charging step under the conditions shown in FIG. . The conditions for CCCV charging are as follows.
CC current: 0.7 C, CV voltage: 4.1 V, end current: 0.01 C.

<Comparative Example 2>
A battery was manufactured in the same manner as in Example 1 except that the initial charging process was performed on the assembled uncharged battery under the conditions shown in FIG. The conditions for CCCV charging are as follows.
CC current: 0.7 C, CV voltage: 4.1 V, end current: 0.01 C.

<Comparative Example 3>
As shown in FIG. 4, the assembled uncharged battery is first charged at a constant current until the battery voltage is charged to 3.4 V with a current value of 0.1 C, and charged to 3.4 V. A battery was produced in the same manner as in Example 1 except that CCCV charging was performed on the obtained battery. The conditions for CCCV charging are as follows.
CC current: 0.7 C, CV voltage: 4.1 V, end current: 0.01 C.

<Comparative example 4>
As shown in Table 1 below, a battery was produced in the same manner as in Example 1 except that the additive was VC.

<Comparative Example 5>
As described below, a battery was manufactured in the same manner as in Example 1 except that the initial charging step was performed under the conditions shown in FIG.

A first CCCV charge was performed on the assembled uncharged battery. The conditions for the first CCCV charge are as follows.
CC current: 0.1 C, CV voltage: 2.9 V, end current: 0.01 C.

The first CCCV discharge was performed on the battery charged to 2.9V. The conditions for the first CCCV discharge are as follows.
CC current: 0.1 C, CV voltage: 2.5 V, end current: 0.01 C.

  The battery discharged to 2.5 V was subjected to the second CCCV charge under the same conditions as the first CCCV charge.

  A second CCCV discharge was performed on the battery charged to 2.9 V under the same conditions as the first CCCV discharge.

  The battery discharged to 2.5 V was subjected to the third CCCV charge under the same conditions as the first CCCV charge.

A fourth CCCV charge was performed on the battery charged to 2.9V. The conditions for the fourth CCCV charge are as follows.
CC current 0.7C, CV voltage 4.1V, end current: 0.01C.

<Initial capacity measurement test>
CCCV discharge was performed on the batteries according to the examples and comparative examples that had undergone the initial charging step under the following conditions, and the initial capacity [Ah] was measured. The results are shown in the column “Initial capacity” in Table 1 below. In Table 1 below, the value shown in “Initial capacity” is a relative evaluation of the battery capacities of other examples and comparative examples with the initial capacity of comparative example 3 as 100%. A larger initial capacity value indicates a higher initial capacity of the battery.
CCCV discharge conditions: CC current value 0.7C, CV voltage 3.0V, end current 0.01C.

<High temperature storage test>
CCCV charging was performed on the batteries according to the examples and comparative examples that had undergone the initial capacity measurement test under the following conditions, and the SOC of the battery was adjusted to 100% at 25 ° C. The battery was stored for 7 days in a thermostat set at 60 ° C. Seven days later, the battery was taken out, and the capacity after high temperature storage was measured in the same manner as the initial capacity. The capacity retention rate after high temperature storage was calculated by dividing the capacity after high temperature storage by the initial capacity. The results are shown in the column of “Capacity maintenance ratio after high temperature storage” in Table 1. It shows that the battery capacity maintenance rate after a high temperature storage test is so large that the value of the capacity maintenance rate after high temperature storage is large.
CCCV charge condition: CC current value 0.7C, CV voltage 4.1V, end current 0.01C.

<Initial IV resistance measurement test>
An IV resistance measurement test was performed on the batteries according to the examples and comparative examples in the initial state. The batteries according to the examples and comparative examples in the initial state were charged in an environment at a temperature of 25 ° C., and adjusted to a charged state of SOC 50%. Thereafter, pulse charging was performed at 25 ° C. with a current of 5 C for 10 seconds, and the IV resistance value (mΩ) was calculated from the amount of voltage increase 10 seconds after the start of charging. The results are shown in Table 1 below. In Table 1 below, the value shown in “IV resistance” is a relative evaluation of IV resistance values of other examples and comparative examples, with the initial IV resistance value of comparative example 3 being 100%. The smaller the value is, the smaller the initial IV resistance value is.

<Result>
As shown in Table 1, Examples 1 to 3 were excellent in initial capacity and capacity retention after high-temperature storage as compared with Comparative Examples 1 to 5. Therefore, it is understood that when a non-aqueous electrolyte containing DME is used, a battery manufacturing method is provided in which the co-insertion of DME into the negative electrode is suppressed and the decrease in battery capacity is suppressed. Moreover, compared with Comparative Examples 1-5, Examples 1-3 were also confirmed that the initial IV resistance value is small.

  From comparison between Examples 1 to 3 and Comparative Examples 2, 3 and 5, it was assumed that a non-aqueous electrolyte solution containing 20% by volume or more of DME and 0.1 mol / L or more and 0.6 mol / L or less of PS was used. However, it was shown that the initial capacity and the capacity retention rate after high-temperature storage are inferior to those of the examples unless step charging is performed in the range of 2.5 V to 2.9 V in the initial charging process. In Examples 1 to 3, since step charging is performed in the range of 2.5 V to 2.9 V, a part of DME co-inserted into the graphite included in the negative electrode mixture layer is desorbed from the graphite. At the same time, it is considered that DME is suppressed from being inserted into the interior of the graphite.

  Comparison between Examples 1 to 3 and Comparative Examples 1 and 4 showed that a battery having excellent initial capacity and capacity retention after high-temperature storage can be obtained by using PS as an additive. In addition, Examples 1 to 3 had smaller initial IV resistance values than Comparative Examples 1 and 4. By using PS as an additive, it is considered that a low-resistance mixed coating composed of DME and PS is formed on the negative electrode, and that the mixed coating suppresses co-insertion of DME into graphite.

  The above embodiments and examples are illustrative in all respects and not restrictive. The technical scope defined by the claims includes meanings equivalent to the claims and all modifications within the scope.

Claims (1)

A method for producing a non-aqueous electrolyte secondary battery comprising a negative electrode and a non-aqueous electrolyte,
A battery preparation step of preparing an uncharged non-aqueous electrolyte secondary battery;
For the non-charged non-aqueous electrolyte secondary battery, a constant current continuously at a predetermined current rate for a plurality of times at a predetermined voltage increment in a range of at least 2.5 V to 2.9 V until a target voltage is reached. Including an initial charging step for performing constant voltage charging,
The negative electrode includes a negative electrode mixture layer containing graphite,
The non-aqueous electrolyte contains 20% by volume or more of dimethoxyethane and 0.1 to 0.6 mol / L of 1,3-propane sultone,
A method for producing a non-aqueous electrolyte secondary battery.