JP2017117582A - Method for producing nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the malleability of a granulated material while suppressing the worsening of a battery performance.SOLUTION: A method for producing a nonaqueous electrolyte secondary battery comprises the steps of: (S01) preparing a granulated material including part of solvent components of an electrolytic solution; and (S02) producing at least one of positive and negative electrodes from the granulated material. The producing step includes: rolling the granulated material; and disposing the granulated material on a surface of a current collector. The boiling point of part of the solvent components of the electrolytic solution is higher than a maximum achievable temperature of the granulated material in the producing step.SELECTED DRAWING: Figure 1

Description

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

  JP-A-2015-174024 (Patent Document 1) includes three rolls arranged in parallel, and the granulated body can be rolled in the first roll gap and rolled in the second roll gap. An electrode manufacturing apparatus configured to transfer the granulated body to a substrate is disclosed.

JP-A-2015-174024

  The granulated body is an aggregate (granular body) of composite particles containing an electrode active material, a binder, a solvent, and the like. Patent Document 1 discloses a method of manufacturing an electrode by rolling the granulated body into a sheet shape with a roll gap and further transferring it to a base material (current collector).

  However, depending on the composition of the granulated product, its spreadability is not sufficient, and the granulated product may be broken during rolling and transfer, and surface defects such as pinholes and stripes may occur in the manufactured electrode.

  In order to enhance the spreadability of the granulated body, it is also conceivable to increase the amount of the solvent contained in the granulated body. However, according to this aspect, the battery manufacturing cost increases, such as a longer drying time. Further, if the solvent remains on the electrode and is brought into the battery, the battery performance may be deteriorated.

  The present invention has been made in view of the above problems. In other words, an object of the present invention is to improve the spreadability of the granulated body while suppressing a decrease in battery performance.

  The manufacturing method of this invention is a manufacturing method of a non-aqueous electrolyte secondary battery provided with a positive electrode, a negative electrode, and electrolyte solution. The manufacturing method includes a step of preparing a granulated body containing a part of the solvent component of the electrolytic solution, and a step of manufacturing at least one of a positive electrode and a negative electrode using the granulated body. The manufacturing step includes rolling the granulated body and disposing the granulated body on the surface of the current collector. The boiling point of a part of the solvent component of the electrolytic solution to be contained in the granulated body is higher than the highest achieved temperature of the granulated body in the production step.

  The present invention will be described below. In the following description, the nonaqueous electrolyte secondary battery may be abbreviated as “battery”. In the following description, the positive electrode and the negative electrode may be collectively referred to as “electrode”. That is, “electrode” in this specification indicates “at least one of a positive electrode and a negative electrode”.

  In the production method of the present invention, a part of the solvent component of the electrolytic solution is contained in the granule which is the precursor of the electrode. When part of the solvent component is brought into the battery, it is mixed with the electrolytic solution and becomes one piece. Therefore, it may be considered that there is substantially no adverse effect on battery performance due to a part of the solvent component remaining on the electrode. Therefore, it is less necessary to increase the drying time of the granulated body as the amount of solvent increases. That is, the extensibility of the granulated body can be improved while suppressing a decrease in battery performance or an increase in battery manufacturing cost.

  However, a part of the solvent component of the electrolytic solution contained in the granule is required not to volatilize in the process of processing the granule into an electrode. In other words, the boiling point of the solvent component needs to be higher than the highest temperature reached by the granule in the step of manufacturing the electrode. This is because if the solvent volatilizes during the electrode manufacturing process, the effect of improving the spreadability is reduced.

  According to the above, it is possible to improve the spreadability of the granulated body while suppressing a decrease in battery performance.

It is a flowchart which shows the outline of the manufacturing method of the nonaqueous electrolyte secondary battery which concerns on embodiment of this invention. It is the schematic which shows an example of an electrode manufacturing step. It is a 1st graph for demonstrating the relationship between content of the electrolyte solution solvent component in a granulation body, and the extensibility of a granulation body. It is a 2nd graph for demonstrating the relationship between content of the electrolyte-solvent component in a granulation body, and the extensibility of a granulation body. It is a graph for demonstrating the relationship between the density of a negative mix layer, and charging resistance.

  Hereinafter, an embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described. However, this embodiment is not limited to the following description.

<Method for producing non-aqueous electrolyte secondary battery>
The manufacturing method of this embodiment is a manufacturing method of a nonaqueous electrolyte secondary battery provided with a positive electrode, a negative electrode, and an electrolytic solution. The nonaqueous electrolyte secondary battery is typically a lithium (Li) ion battery.

  FIG. 1 is a flowchart showing an outline of the manufacturing method of the present embodiment. The production method of the present embodiment includes a granule preparation step (S01), an electrode production step (S02), an electrode group production step (S03), a case accommodation step (S04), and a liquid injection step (S05). Hereinafter, each step will be described.

<< Granulate Preparation Step (S01) >>
In the granule preparation step, a granule containing a part of the solvent component of the electrolytic solution is prepared. Hereinafter, for convenience, a part of the solvent component of the electrolytic solution contained in the granulated body in this step may be referred to as “electrolytic solution solvent component”. In the following description, when simply referred to as “solvent”, a solvent that is not a solvent component of an electrolyte solution (for example, water, N-methyl-2-pyrrolidone (NMP)) or the like is indicated.

  The granulated body can be prepared by mixing an electrode active material, a binder, a solvent, and an electrolyte solution solvent component. A conventionally known agitation granulator can be used for the preparation of the granulated body.

  From the viewpoint of dispersibility of the solid content in the granulated body, it is preferable to mix the solid content in advance before mixing with the liquid (solvent and electrolyte solution solvent component). As a specific embodiment, it is conceivable to prepare a premix by previously mixing an electrode active material and a binder, and then add a liquid to the premix and granulate. The solid content rate of the granulated body is, for example, about 65 to 85% by mass (typically about 75% by mass). “Solid content” indicates a component other than the solvent and the electrolyte solution solvent component among the components contained in the granulated product, and “solid content rate” indicates a mass ratio occupied by the solid content in the granulated product. Yes.

The d ₅₀ of the granulated body can be adjusted by the solid content rate, the stirring speed, the stirring time, and the like. The d ₅₀ of the granulated body is preferably about 0.5 to 10 mm, more preferably about 0.5 to 5 mm, and still more preferably about 0.5 to 2 mm. Here, “d ₅₀ ” indicates a particle size of 50% cumulative from the fine particle side in the volume-based particle size distribution. When d ₅₀ of the granules is too large, when rolling the granule, easily granules (particles) is clogged roll gap, the productivity may be lowered.

(Electrode active material)
The electrode active material may be any material that can electrochemically occlude and release charge carriers (typically Li ions). When producing a positive electrode in this step, the electrode active material (positive electrode active material) is, for example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Co _1/3 Mn _1/3 O _2, etc. Li-containing metal oxide may be used. Moreover, when manufacturing a negative electrode in this step, the electrode active material (negative electrode active material) may be graphite, graphitizable carbon, non-graphitizable carbon, or the like. In the solid content of the granulated body, the mass ratio of the electrode active material is, for example, about 80 to 99% by mass.

(Binder)
The binder may be any material that can bind the electrode active materials and the electrode active material and the current collector. The binder may be, for example, carboxymethyl cellulose (CMC), polyacrylic acid (PAA), styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), and the like. In the solid content of the granulated body, the mass ratio of the binder is, for example, about 1 to 10% by mass.

(solvent)
Solvents other than the electrolyte solvent component can be appropriately selected in consideration of the dispersibility of the binder. The solvent may be water, NMP or the like, for example. The water is preferably water in which impurities such as ion exchange water are reduced.

(Electrolyte solvent component)
The electrolyte solvent component is a substance whose boiling point is higher than the highest temperature of the granulated body in the electrode manufacturing step described later. Considering that the drying operation is performed in the electrode manufacturing step, the boiling point of the electrolyte solution solvent component is preferably 200 ° C. or higher. Here, “boiling point” means that when the temperature of the liquid is gradually increased, the vapor pressure of the liquid becomes equal to the standard atmospheric pressure (101.3 kPa), that is, when gas (bubbles) is first generated. It shall indicate the temperature (initial boiling point) of the liquid.

  Examples of the electrolyte solution solvent component include ethylene carbonate (EC; boiling point 238 ° C.), propylene carbonate (PC; boiling point 242 ° C.), butylene carbonate (BC; boiling point 240 ° C.), and γ-butyrolactone (GBL; boiling point 204 ° C.). Examples thereof include cyclic carbonates and mixtures thereof. That is, the electrolyte solution solvent component may be at least one cyclic carbonate selected from the group consisting of EC, PC, BC, and GBL. From the viewpoint of battery performance, the cyclic carbonate is preferably at least one of EC and PC.

  The spreadability of the granulated body tends to improve as the amount of the electrolyte solvent component increases. However, when the amount of the electrolyte solvent component is excessively large, granulation and film formation become difficult, for example, the granulated body becomes coarse. From these viewpoints, the amount of the electrolyte solvent component contained in the granulated body is preferably 1% by mass or more and 15% by mass or less, more preferably 2.5% by mass or more and 15% by mass with respect to the entire granulated body. It is not more than mass%, and more preferably not less than 5 mass% and not more than 10 mass%.

(Other ingredients)
In the present embodiment, the granulated body may be prepared so that the granulated body contains components other than the above-described electrode active material, binder, solvent, and electrolyte solution solvent component. For example, the granulated body may be prepared so as to contain a conductive material such as carbon black. In the solid content of the granulated body, the mass ratio of the conductive material is, for example, about 1 to 10% by mass.

<< Electrode manufacturing step (S02) >>
In the electrode manufacturing step, at least one of the positive electrode and the negative electrode is manufactured from the granulated body. The positive electrode and the negative electrode are, for example, strip-shaped sheet members.

  In the above-described granule preparation step, when a granule containing a positive electrode active material is prepared, a positive electrode can be produced, and a granule containing a negative electrode active material is prepared A negative electrode can be manufactured. In the present embodiment, either the positive electrode or the negative electrode may be manufactured from the granulated body, or both the positive electrode and the negative electrode may be manufactured from the granulated body. In addition, the electrode which is not manufactured with a granulated body can be manufactured by applying a conventionally well-known slurry (paint) to the surface of a collector.

  The electrode manufacturing step of the present embodiment includes rolling the granulated body (rolling operation) and disposing the granulated body on the surface of the current collector (arranging operation). As described below, one aspect of “arranging” includes “transferring”. The rolling operation and the placement operation may be performed in this order, may be performed one after the other, or may be performed simultaneously. The electrode manufacturing step may further include heating the granulated body (drying operation) and the like.

(Electrode manufacturing equipment)
FIG. 2 is a schematic diagram illustrating an example of an electrode manufacturing step. The electrode manufacturing apparatus 90 shown in FIG. 2 includes three rolls, that is, an A roll 91, a B roll 92, and a C roll 93. Each roll is rotationally driven by a driving device (not shown). The curved arrows drawn on each roll indicate the rotation direction of each roll.

  The granulated body 10 </ b> A (granular body) is supplied to the gap between the A roll 91 and the B roll 92. A predetermined load is applied to the A roll 91. In the gap between the A roll 91 and the B roll 92, the granulated body 10A is rolled and formed into a sheet-like granulated body 10B.

  The granulated body 10 </ b> B (sheet body) is conveyed by the B roll 92 and supplied to the gap between the B roll 92 and the C roll 93. The current collector 11 is conveyed by the C roll 93 and supplied to the gap between the B roll 92 and the C roll 93. When manufacturing the positive electrode, the current collector 11 is, for example, an aluminum (Al) foil, and when manufacturing the negative electrode, the current collector 11 is, for example, a copper (Cu) foil.

  In the gap between the B roll 92 and the C roll 93, the granulated body 10B is rubbed against the current collector 11. Thereby, the granulated body 10 </ b> B is pressure-bonded to the current collector 11, and the granulated body 10 </ b> B is disposed on the surface of the current collector 11. That is, the granulated body 10 </ b> B is transferred from the surface of the B roll 92 to the surface of the current collector 11.

  By arranging the granulated body 10B on the surface of the current collector 11, the granulated body 10B becomes an electrode mixture layer (a positive electrode mixture layer or a negative electrode mixture layer). Thereafter, the granulated body 10B may be dried by heating the granulated body 10B. The drying operation can be performed by a drying furnace (not shown). When the granulation is dried, the granulation may reach the maximum temperature in this step. The maximum reached temperature of the granulated body in this step is, for example, about 90 to 180 ° C.

  Furthermore, an electrode (a positive electrode or a negative electrode) can be manufactured by performing compression, cutting, or the like according to the specifications of the battery.

  In this embodiment, since the granulated body contains an electrolyte solution solvent component, the spreadability of the granulated body is high. Therefore, when the granulated body 10A is rolled and when the granulated body 10B is transferred, problems such as tearing of the granulated body are suppressed. That is, surface defects such as pinholes and streaks are reduced in the electrode after the granulated body is transferred.

  Moreover, in the conventional granulated body, it was difficult to form an electrode mixture layer having a low density. However, according to the granulated body of this embodiment, an electrode mixture layer having a low density can also be formed. .

  Conventionally, the reason why it is difficult to form a low-density electrode mixture layer is that when a granulated body 10B (sheet body) having a low density is formed in the gap between the A roll 91 and the B roll 92, In the gap between the B roll 92 and the C roll 93, the granulated body 10B is crushed. Since the granulated body of this embodiment has high spreadability and extends well, transfer is possible without being excessively crushed even in a low density state. By reducing the density of the electrode mixture layer, reduction of internal resistance, that is, improvement of input / output characteristics can be expected.

<< Electrode Group Manufacturing Step (S03) >>
In the electrode group manufacturing step, an electrode group including a positive electrode and a negative electrode is manufactured. The electrode group is manufactured by, for example, using a predetermined winding device, laminating the positive electrode and the negative electrode with the separator interposed therebetween, and further winding the electrode. The separator is a porous sheet made of, for example, polyethylene (PE), polypropylene (PP), or the like.

<< Case Housing Step (S04) >>
In the case housing step, the electrode group is housed in a predetermined battery case. The battery case may be a rigid case such as a square shape or a cylindrical shape, or may be a soft case constituted by an aluminum laminate film or the like.

<< Injection step (S05) >>
In the liquid injection step, a predetermined electrolytic solution is injected into the battery case. The electrolytic solution is a liquid electrolyte in which a Li salt is dissolved in an aprotic organic solvent.

The aprotic organic solvent may be, for example, a mixture of the above-described cyclic carbonate such as EC and PC and a chain carbonate. Examples of the chain carbonate include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). The mixing ratio of the cyclic carbonate and the chain carbonate is, for example, volume ratio, and is about cyclic carbonate: chain carbonate = 1: 9 to 5: 5. The Li salt that is a solute may be, for example, LiPF ₆ . The concentration of the Li salt may be about 0.8 to 1.2 mol / liter, for example.

  In this embodiment, the electrolyte solution solvent component remaining in the granulated body (electrode mixture layer) is mixed with the electrolyte solution injected in this step to be integrated. That is, the space where the electrolyte solvent component remains in the electrode mixture layer is replaced with the electrolyte. Using this point, the following modes are also conceivable. That is, by adding EC or the like, which is a high viscosity component of the electrolytic solution, to the electrode mixture layer, the high viscosity component of the electrolytic solution can be reduced and the viscosity of the electrolytic solution can be lowered. According to such an embodiment, the permeability of the electrolytic solution to the electrode group is improved, and the impregnation time can be shortened or the battery performance can be expected to be improved.

  After injecting the electrolytic solution, the battery case is sealed by a predetermined means, thereby completing the non-aqueous electrolyte secondary battery of this embodiment. The non-aqueous electrolyte secondary battery of the present embodiment has good yield because there are few defects in the electrode process, and the input / output characteristics are reduced by reducing the density of the electrode mixture layer (granulated body). It can be an excellent battery. A non-aqueous electrolyte secondary battery having excellent input / output characteristics has high utility value as a drive power source for automobiles, for example.

  Hereinafter, although this embodiment is described using an example, this embodiment is not limited to the following example.

<Manufacture of non-aqueous electrolyte secondary batteries>
A granulated body was prepared under various conditions as described below, and an evaluation battery was manufactured using the granulated body.

Example 1
1. Granule preparation step (S01)
The following negative electrode materials were prepared.

(Negative electrode material)
Electrode active material: Graphite Binder: CMC and SBR
Solvent: ion-exchanged water current collector: Cu foil.

  A premix was prepared by stirring and mixing graphite, CMC and SBR. The solid content of the negative electrode was in a mass ratio of graphite: (CMC and SBR) = 95: 5.

Ion-exchanged water and PC (electrolyte solvent component) were added to the preliminary mixture, and the mixture was stirred and mixed to prepare a granulated body. The content of the electrolytic solution solvent component in the granulated body was 5% by mass (mass%). The d ₅₀ of the granulated body was less than 10 mm.

2. Electrode manufacturing step (S02)
The granulated body 10A and the current collector 11 (Cu foil) are supplied to the electrode manufacturing apparatus 90 shown in FIG. (Cu foil). Thereafter, the granulated body was heated to evaporate ion exchange water as a solvent. At this time, the maximum reached temperature of the granulated body was 110 ° C. Furthermore, the negative electrode was manufactured by compressing to a predetermined dimension and cutting. The density of the electrode mixture layer (the density of the granulated body after compression) was 1.27 g / cm ³ .

  The following positive electrode materials were prepared.

(Positive electrode material)
Electrode active material: nickel cobalt lithium manganate (NCM)
Conductive material: Acetylene black (AB; a kind of carbon black)
Binder: PVdF
Solvent: NMP
Current collector: Al foil.

  A granulated body was prepared using the above positive electrode material, and a positive electrode was produced from the granulated body. This time, no electrolyte solvent component is used in the positive electrode. The solid content of the positive electrode was NCM: AB: PVdF = 90: 5: 5 by mass ratio.

3. Electrode group manufacturing step (S03)
An electrode group including the positive electrode and the negative electrode was manufactured by laminating the positive electrode and the negative electrode with a predetermined separator interposed therebetween.

4). Case accommodation step (S04)
The electrode group was accommodated in a battery case made of an aluminum laminate film.

5. Injection step (S05)
An electrolyte solution was injected into the battery case, and then the battery case was sealed. The composition of the electrolytic solution is [1 mol / liter LiPF ₆ , EC: DMC: EMC = (30−x): 40: 30 (mass ratio)]. Here, “x” represents a mass part of the electrolyte solution solvent component (PC or EC) contained in the negative electrode. That is, by mixing the electrolyte solution of such composition with the electrolyte solvent component contained in the negative electrode, the solvent composition of the electrolyte solution in the battery is
(Total of EC and PC): DMC: EMC = 30: 40: 30 (mass ratio)
It becomes. From the above, the battery according to Example 1 was manufactured.

<< Examples 2 and 3 >>
As shown in Table 1 below, except that the PC content of the granulated body was changed and the rolling and transfer conditions were adjusted so that the density of the electrode mixture layer was lower than that of Example 1. In the same manner as in Example 1, batteries according to Examples 2 and 3 were produced.

<< Examples 4 to 6 >>
Batteries according to Examples 4 to 6 were produced in the same manner as in Examples 1 to 3, except that the electrolyte solvent component in the granule preparation step was changed to EC.

Example 7
The negative electrode of Example 4 was rolled again to produce a negative electrode in which the electrode mixture layer was densified. A battery according to Example 7 was manufactured using the negative electrode.

<< Reference Examples 1 and 2 >>
As shown in Table 1 below, an attempt was made to produce an electrode in the same manner as in the above example except that the PC content and the EC content were changed. However, the granulated body was coarsened, and the granulated body was clogged with the roll gap during rolling, and it was difficult to produce an electrode that could be compared with the other examples.

<< Examples 8 to 11 >>
As shown in Table 1 below, batteries according to Examples 8 to 11 were manufactured in the same manner as in the above Examples except that the PC content and the EC content were changed.

<< Comparative Examples 1-3 and Reference Example 3 >>
In the granule preparation step, batteries according to Comparative Examples 1 to 3 were manufactured in the same manner as in the above example except that the granule did not contain an electrolyte solution solvent component. In Reference Example 3, an attempt was made to produce an electrode by setting the target density to 1.2 g / cm ³ (low density). Was difficult.

<Evaluation>
1. Evaluation of the spreadability of the granulate The spreadability of the granulate prepared in the granule preparation step of each example was evaluated. Specifically, the granulated body was gradually rolled thin while gradually reducing the roll gap, and the load when the thickness reached 350 μm was measured. The results are shown in Table 1. In Table 1, the smaller the load is, the better the spreadability is.

2. Evaluation of Battery Performance The performance of the batteries manufactured in Examples 1 to 7 and Comparative Examples 1 to 3 was evaluated. The SOC (State Of Charge) of the battery was adjusted to 56%. The battery was placed in a thermostat set to −10 ° C. and left to stand for 2 hours. After 2 hours, the charging resistance of the battery was measured in the same environment. The results are shown in Table 1. In Table 1, the lower the charging resistance, the better the battery performance (input characteristics).

<Discussion>
1. FIG. 3 is a first graph for explaining the relationship between the content of the electrolyte solvent component in the granulated body and the spreadability of the granulated body. From FIG. 3, it can be seen that the extensibility of the granulated body is greatly improved by adding the electrolyte solution solvent component to the granulated body.

  The spreadability of the granulated body is improved as the content of the electrolyte solvent component increases. However, as described above, when the content of the electrolyte solvent component exceeds 15% by mass, granulation and film formation become difficult (see Reference Examples 1 and 2 in Table 1 above).

  FIG. 4 is a second graph for explaining the relationship between the content of the electrolyte solvent component in the granulated body and the extensibility of the granulated body. FIG. 4 shows the spreadability in a region where the content of the electrolyte solvent component is small. Even in a region where the electrolyte solvent component is small, the effect of improving the spreadability is recognized as the content of the electrolyte solvent component increases.

  From the above results, the content of the electrolytic solution solvent component in the granulated body is preferably 1% by mass or more and 15% by mass or less, more preferably 2.5% by mass or more and 15% by mass or less, and still more preferably. Is 5 mass% or more and 10 mass% or less.

2. FIG. 5 is a graph for explaining the relationship between the density of the negative electrode mixture layer and the charging resistance. From FIG. 5, improvement in the low-temperature charging resistance is recognized as the density of the negative electrode composite material layer (the density of the granulated body after rolling) decreases. This is presumably because the contact area (that is, the reaction area) between the electrolytic solution and the electrode active material is increased.

However, it is difficult to achieve a density of 1.3 g / cm ³ or less when the granule does not contain an electrolyte solvent component (see Comparative Examples 1 to 3 and Reference Example 3 in Table 1 above). ).

A density of 1.3 g / cm ³ or less can be realized by incorporating an electrolyte solvent component into the granulated body. In this study, actually, it is possible to form a negative electrode material layer density is 1.17 g / cm ³ or more 1.30 g / cm ³ or less. As shown in FIG. 5, in such a range, the charging resistance is low and the battery performance is good. The density of thus negative electrode composite material layer is preferably not more than 1.17 g / cm ³ or more 1.30 g / cm ^3.

  The embodiments and examples disclosed herein are illustrative in all aspects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  10A, 10B granulated body, 11 current collector, 90 electrode manufacturing apparatus, 91 A roll, 92 B roll, 93 C roll.

Claims (1)

A method for producing a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and an electrolyte solution,
Preparing a granule containing a part of the solvent component of the electrolytic solution;
Producing at least one of the positive electrode and the negative electrode by the granulated body,
The manufacturing step includes rolling the granulated body, and disposing the granulated body on a surface of a current collector,
The said partial boiling point is a manufacturing method of a non-aqueous-electrolyte secondary battery whose higher than the ultimate temperature of the said granule in the said manufacture step.

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