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US-20260128317-A1 - Dry Electrode for Electrochemical Device and Method for Manufacturing the Same

US20260128317A1US 20260128317 A1US20260128317 A1US 20260128317A1US-20260128317-A1

Abstract

A dry electrode for an electrochemical device includes a dry electrode film as an electrode active material layer. The electrode active material layer includes an electrode active material and a binder resin. The binder resin is fibrillated. The electrode active material layer has an average pore diameter of 5.0 μm or more and a porosity of from 15 vol % to 50 vol %, wherein the average pore diameter is calculated based on a longest pore diameter. The large pore diameter of the electrode active material leads to easy lithium (Li) migration, low Li diffusion resistance and fast lithium movement, thereby reducing or suppressing overvoltage, and improving high rate charge/discharge characteristics. Also provided is a method of manufacturing a dry electrode film.

Inventors

  • Dong-mok Shin
  • Joo-Nam Park
  • Moon-soo Park
  • Dong-Ch Shin

Assignees

  • LG ENERGY SOLUTION LTD.

Dates

Publication Date
20260507
Application Date
20240812
Priority Date
20230810

Claims (20)

  1. 1 . A dry electrode for an electrochemical device, comprising: a dry electrode film as an electrode active material layer, wherein the electrode active material layer includes an electrode active material and a binder resin, wherein the binder resin is fibrillated, and wherein the electrode active material layer has an average pore diameter of 5.0 μm or more and a porosity of from 15 vol % to 50 vol %, wherein the average pore diameter is calculated based on a longest pore diameter.
  2. 2 . The dry electrode for the electrochemical device according to claim 1 , wherein the average pore diameter of the electrode active material layer is 6.0 μm or more.
  3. 3 . The dry electrode for the electrochemical device according to claim 1 , wherein the average pore diameter of the electrode active material layer is 6.5 μm or more.
  4. 4 . The dry electrode for the electrochemical device according to claim 1 , wherein in the electrode active material layer, an average diameter of pores having a diameter of from 4 μm to 8 μm is 6.5 μm or more.
  5. 5 . The dry electrode for the electrochemical device according to claim 1 , wherein in the electrode active material layer, a ratio of a number of pores having a diameter from 4 μm to 8 μm to a total number of pores is 80% or more.
  6. 6 . The dry electrode for the electrochemical device according to claim 1 , wherein in the electrode active material layer, a ratio of a volume of pores having a diameter of from 4 μm to 8 μm to a total pore volume is 60% or more.
  7. 7 . The dry electrode for the electrochemical device according to claim 1 , wherein in the electrode active material layer, a geodesic tortuosity (τ geo ) according to the following Equation 1 is 1.15 or less: τ g ⁢ e ⁢ o = L eff L [ Equation ⁢ 1 ] wherein, L denotes a thickness of the electrode active material layer, and L eff denotes a lithium ion movement path length in the electrode active material layer.
  8. 8 . The dry electrode for the electrochemical device according to claim 7 , wherein in the electrode active material layer, a physical tortuosity (τ phy ) according to the following Equation 2 is 3 or less: τ p ⁢ h ⁢ y = ε ⁢ σ 0 σ eff [ Equation ⁢ 2 ] wherein, ε denotes a porosity of the electrode active material layer, δ 0 denotes an electrolyte conductivity, and δ eff denotes an effective electrolyte conductivity by a pore structure.
  9. 9 . The dry electrode for the electrochemical device according to claim 1 , wherein the binder resin includes polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyolefin, or a mixture of two or more of them.
  10. 10 . The dry electrode for the electrochemical device according to claim 1 , wherein a degree of crystallinity of the dry electrode film is from more than 0% to 10% or less.
  11. 11 . The dry electrode for the electrochemical device according to claim 1 , wherein the binder resin includes fibrillated fibrils of which parts have a diameter of 1 μm or more.
  12. 12 . The dry electrode for the electrochemical device according to claim 11 , wherein the fibrillated binder resin includes the fibrillated fibrils of which the parts having the diameter of 1 μm or more are 5 μm or more in length.
  13. 13 . A method for manufacturing a dry electrode film according to claim 1 , comprising: preparing a powdery blend including an electrode active material, a conductive material, and a binder resin; kneading the powdery blend at a temperature ranging between 70° C. and 200° C. to prepare a bulk blend; grinding the bulk blend to obtain an electrode powder; and calendering the electrode powder.
  14. 14 . The method for manufacturing the dry electrode film according to claim 13 , wherein a D50 of the electrode powder obtained by the grinding of the bulk blend ranges from 100 μm to 700 μm.
  15. 15 . The dry electrode for the electrochemical device according to claim 1 , wherein the average pore diameter of the electrode active material layer ranges from 5 μm to 20 μm.
  16. 16 . The dry electrode for the electrochemical device according to claim 1 , wherein the dry electrode film has a Quantified Binder Ratio (QBR) ranging between 0.9 and 1.1 according to the following Relation Equation 3: QBR ⁢ = B ⁢ s / B ⁢ f [ Relation ⁢ equation ⁢ 3 ] wherein, Bs denotes an average fluorine content in an electrode active material layer surface within 15% of a total thickness of the electrode active material layer from an outermost surface of the electrode active material layer and Bf denotes an average fluorine content in an electrode active material layer bottom area within 15% of a total thickness of the electrode active material layer from an electrode active material layer interface in contact with a current collector.
  17. 17 . The dry electrode for the electrochemical device according to claim 1 , wherein the average pore diameter has a small deviation of pore size in the electrode active material layer for making lithium migration easy and leading to low lithium diffusion resistance and fast lithium transport to suppress overvoltage.
  18. 18 . The dry electrode for the electrochemical device according to claim 11 , wherein the fibrillated binder resin includes the fibrillated fibrils of which the parts having the diameter of 1 μm or more are 50 μm or more in length.
  19. 19 . The dry electrode for the electrochemical device according to claim 1 , wherein in the electrode active material layer, a ratio of a volume of pores having a diameter of from 4 μm to 8 μm to a total pore volume is 65% or more.
  20. 20 . The dry electrode for the electrochemical device according to claim 1 , wherein flat bar shaped pores are included at 43 vol % or more based on a total pore volume 100 vol % of the electrode.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/KR2024/012023 filed Aug. 12, 2024, which claims priority to Korean Patent Application No. 10-2023-0105146 filed on Aug. 10, 2023, the disclosures of which are incorporated herein by reference. TECHNICAL FIELD The present disclosure relates to a dry electrode for an electrochemical device including a dry electrode film. Additionally, the present disclosure relates to a method for manufacturing the same. BACKGROUND Due to the increasing use of fossil fuels, there is a growing demand for the use of alternative energy and clean energy, and in such circumstances, many studies are being made in the field of energy generation and storage using electrochemistry. Currently, a typical example of electrochemical devices using electrical and chemical energy is secondary batteries, and the range of application of secondary batteries is gradually expanding. One of typical secondary batteries, lithium secondary batteries, are used as not only an energy source of mobile devices but also a power source of electric vehicles and hybrid electric vehicles as an alternative to vehicles using fossil fuels such as gasoline vehicles and diesel vehicles that are regarded as one of the main causes of air pollution, and the range of application of lithium secondary batteries is expanding to an auxiliary power source through a grid. A process of manufacturing a lithium secondary battery is largely classified into three steps; an electrode manufacturing process, an electrode assembly manufacturing process and a formation/ageing process. The electrode manufacturing process is sub-classified into an electrode material mixing process, an electrode coating process, a drying process, a rolling process, a slitting process and a winding process. Among them, the electrode material mixing process is a process of mixing the components for forming an electrode active layer in which electrochemical reaction actually occurs in the electrode, and specifically, mixing an electrode active material which is the essential element of the electrode with an additive such as a conductive material, fillers, a binder for binding powder and adhering to a current collector, and a solvent for imparting viscosity and dispersing power to prepare a flowable slurry. The mixed composition for the formation of the electrode active material is referred to as an electrode mixture in broad sense. Subsequently, the electrode coating process of applying the electrode mixture to an electrically conductive current collector, and the drying process for removing a solvent contained in the electrode mixture are performed, and additionally the electrode is rolled to a predetermined thickness. Meanwhile, as the solvent included in the electrode mixture evaporates in the drying process, defects such as pin holes or cracks may occur in the already formed electrode active layer. Additionally, the active layer is not uniformly dried all over the entire inner/outer area, and due to a difference in solvent evaporation rate, some regions get dry earlier and the powder at the corresponding regions floats, and some other regions get dry later at a time interval, resulting in low quality of the electrode. To solve this problem, efforts have been devoted to dryers for uniformly drying the inner and outer area of the active layer and adjusting the solvent evaporation rate, but these dryers are very expensive and require a considerate amount of costs and time to operate them, so it is disadvantageous in terms of manufacturing process. Accordingly, recently, many studies are being made to manufacture dry electrodes without solvents. The manufacture of dry electrodes has eco-friendliness, process simplification and cost saving effects. Additionally, in the manufacture of wet electrodes, binder resin migration occurs during the drying of an electrode slurry, but such binder resin migration does not occur in the manufacture of dry electrodes, so the manufactured electrodes have uniform binder resin distribution in the thickness direction. By the uniform binder resin distribution, battery capacity decline, performance degradation and short life problems may be prevented. However, in the manufacture of dry electrodes, when the binder resin is fibrillated too finely or the pore size is small, the narrow pores impede the migration of Li ions, causing a decline in electrode capacity during high rate charging/discharging. Accordingly, in addition to uniform binder/conductive material distribution in the vertical direction (thickness direction) of the electrodes, there is a need for electrode structure design for fast ion transport to improve high rate charge/discharge. The present disclosure needs to study the structure control of dry electrode films that is effective for high rate charge/discharge through an optimal level of kneading process. Technical Problem Th