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US-12626923-B2 - Energy storage device and method for manufacturing energy storage device

US12626923B2US 12626923 B2US12626923 B2US 12626923B2US-12626923-B2

Abstract

An energy storage device according to one aspect of the present invention is an energy storage device including a negative electrode having a negative electrode substrate and a negative active material layer stacked on the negative electrode substrate directly or via another layer, and a nonaqueous electrolyte solution, in which the negative active material layer contains graphite and a solvent-based binder, and the negative active material layer is not subjected to pressing.

Inventors

  • Kenta OGI
  • Yuhei Itai
  • Kei KUMABAYASHI
  • Fumiya NAKANO

Assignees

  • GS YUASA INTERNATIONAL LTD.

Dates

Publication Date
20260512
Application Date
20201105
Priority Date
20191118

Claims (16)

  1. 1 . An energy storage device comprising a negative electrode having a negative electrode substrate and a negative active material layer stacked on the negative electrode substrate, and a nonaqueous electrolyte solution, wherein the negative active material layer contains graphite and a solvent-based binder, the graphite contains artificial solid graphite having an average particle size of 10 μm or less, an area ratio excluding voids in a particle of the artificial solid graphite to a total area of the particle of the artificial solid graphite is 95% or more in a cross section of the particle of the artificial solid graphite observed in a scanning electron microscope (SEM) image, and the negative active material layer is not subjected to pressing.
  2. 2 . An energy storage device comprising a negative electrode having a negative electrode substrate and a negative active material layer stacked on the negative electrode substrate, and a nonaqueous electrolyte solution, wherein the negative active material layer contains graphite and a solvent-based binder, the graphite contains artificial solid graphite having an average particle size of 10 μm or less, an area ratio excluding voids in a particle of the artificial solid graphite to a total area of the particle of the artificial solid graphite is 95% or more in a cross section of the particle of the artificial solid graphite observed in a scanning electron microscope (SEM) image, and a ratio of surface roughness of the negative electrode substrate in a region without the negative active material layer stacked to surface roughness of the negative electrode substrate in a region with the negative active material layer stacked is 0.90 or more.
  3. 3 . The energy storage device according to claim 1 , wherein the negative active material layer has a porosity of 35% or less.
  4. 4 . The energy storage device according to claim 1 , wherein the negative active material layer does not contain scale-like graphite particles.
  5. 5 . A method for manufacturing an energy storage device, the method comprising: stacking a negative active material layer on a negative electrode substrate; and preparing a nonaqueous electrolyte solution, wherein the negative active material layer contains graphite and a solvent-based binder, the graphite contains artificial solid graphite having an average particle size of 10 μm or less, an area ratio excluding voids in a particle of the artificial solid graphite to a total area of the particle of the artificial solid graphite is 95% or more in a cross section of the particle of the artificial solid graphite observed in a scanning electron microscope (SEM) image, and the method does not comprise subjecting the negative active material layer to pressing.
  6. 6 . The energy storage device according to claim 2 , wherein the negative active material layer has a porosity of 35% or less.
  7. 7 . The energy storage device according to claim 2 , wherein the negative active material layer does not contain scale-like graphite particles.
  8. 8 . The energy storage device according to claim 1 , wherein the negative active material layer has a porosity of 35% or less, and the negative active material layer does not contain scale-like graphite particles.
  9. 9 . The energy storage device according to claim 2 , wherein the negative active material layer has a porosity of 35% or less, and the negative active material layer does not contain scale-like graphite particles.
  10. 10 . The method according to claim 5 , wherein the negative active material layer has a porosity of 35% or less, and the negative active material layer does not contain scale-like graphite particles.
  11. 11 . The energy storage device according to claim 1 , wherein the average particle size of the artificial solid graphite is 3 μm or less.
  12. 12 . The energy storage device according to claim 1 , further comprising a positive electrode having a positive electrode substrate and a positive active material layer stacked on the positive electrode substrate, wherein the positive active material layer contains lithium transition metal composite oxides of LiNi 1/3 Co 1/3 Mn 1/3 O 2 as a positive active material.
  13. 13 . The energy storage device according to claim 2 , wherein the average particle size of the artificial solid graphite is 3 μm or less.
  14. 14 . The energy storage device according to claim 2 , further comprising a positive electrode having a positive electrode substrate and a positive active material layer stacked on the positive electrode substrate, wherein the positive active material layer contains lithium transition metal composite oxides of LiNi 1/3 Co 1/3 Mn 1/3 O 2 as a positive active material.
  15. 15 . The method according to claim 5 , wherein the average particle size of the artificial solid graphite is 3 μm or less.
  16. 16 . The method according to claim 5 , further comprising stacking a positive active material layer on a positive electrode substrate, wherein the positive active material layer contains lithium transition metal composite oxides of LiNi 1/3 Co 1/3 Mn 1/3 O 2 as a positive active material.

Description

TECHNICAL FIELD The present invention relates to an energy storage device and a method for manufacturing the energy storage device. BACKGROUND ART Nonaqueous electrolyte solution secondary batteries typified by lithium ion nonaqueous electrolyte solution secondary batteries are widely in use for electronic equipment such as personal computers and communication terminals, automobiles, and the like because the batteries have high energy density. The nonaqueous electrolyte solution secondary battery is generally provided with an electrode assembly, having a pair of electrodes electrically isolated by a separator, and a nonaqueous electrolyte solution interposed between the electrodes and is configured to charge and discharge by transferring ions between both the electrodes. Capacitors such as lithium ion capacitors and electric double-layer capacitors are also widely in use as energy storage devices except for the nonaqueous electrolyte solution secondary batteries. As a negative active material of the energy storage device, a carbon material such as graphite is used (see Patent Document 1). Patent Document 1 describes an invention of a negative electrode material for a lithium battery containing a carbon-based negative active material with a specific surface area of 1 m2/g or more, a binder material made of styrene butadiene rubber (SBR), and carbon fibers with a fiber diameter of 1 to 1000 nm. Patent Document 1 describes that a negative electrode material composition is applied to a current collector foil, dried, and then subjected to pressing to prepare a negative electrode material. PRIOR ART DOCUMENT Patent Document Patent Document 1: JP-A-2005-222933 SUMMARY OF THE INVENTION Problems to be Solved by the Invention In an energy storage device including a negative electrode having a carbon material as a negative active material and SBR which is a water-based binder as a binder material (binder) as described in Patent Document 1, durability is not sufficient. Specifically, the inventors have confirmed that the energy storage device having the above configuration has a low capacity retention ratio after being left in a charged state. An object of the present invention is to provide an energy storage device which uses graphite as a negative active material and has a high capacity retention ratio after being left in a charged state, and a method for manufacturing the energy storage device. Means for Solving the Problems An energy storage device according to one aspect of the present invention is an energy storage device including a negative electrode having a negative electrode substrate and a negative active material layer stacked on the negative electrode substrate directly or via another layer, and a nonaqueous electrolyte solution, in which the negative active material layer contains graphite and a solvent-based binder, and the negative active material layer is not subjected to pressing. An energy storage device according to another aspect of the present invention is an energy storage device including a negative electrode having a negative electrode substrate and a negative active material layer stacked on the negative electrode substrate directly or via another layer, and a nonaqueous electrolyte solution, in which the negative active material layer contains graphite and a solvent-based binder, and a ratio of surface roughness of the negative electrode substrate in a region without the negative active material layer stacked to surface roughness of the negative electrode substrate in a region with the negative active material layer stacked is 0.90 or more. A method for manufacturing an energy storage device according to another aspect of the present invention is a method for manufacturing an energy storage device, the method including stacking a negative active material layer on a negative electrode substrate directly or via another layer; and preparing a nonaqueous electrolyte solution, in which the negative active material layer contains graphite and a solvent-based binder; and the method does not include subjecting the negative active material layer to pressing. Advantages of the Invention According to one aspect of the present invention, it is possible to provide an energy storage device that uses graphite as a negative active material and has a high capacity retention ratio after being left in a charged state, and a method for manufacturing the energy storage device. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic exploded perspective view illustrating an energy storage device in one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the energy storage device in one embodiment of the present invention. FIG. 3 is a schematic view illustrating an energy storage apparatus configured by aggregating a plurality of the energy storage devices in one embodiment of the present invention. FIG. 4 is SEM image of the artificial graphite A used in Example 1 at the magnificati