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EP-4465379-B1 - POSITIVE ELECTRODE FOR SOLID-STATE BATTERIES AND SOLID-STATE BATTERIES COMPRISING THE SAME

EP4465379B1EP 4465379 B1EP4465379 B1EP 4465379B1EP-4465379-B1

Inventors

  • Kvasha, Andriy
  • THIEU, THO
  • GARCÍA CALVO, Oihane
  • COMBARRO PALACIOS, Izaskun
  • COBOS, Mónica
  • Gutiérrez, Antonio
  • URDAMPILLETA GONZALEZ, Idoia

Dates

Publication Date
20260506
Application Date
20230516

Claims (15)

  1. A positive electrode comprising i) a high voltage cathode active material selected from lithium cobalt oxide LiCoO 2 (LCO); high-voltage spinel LiNi 0.5 Mn 1.5 O 4 (LNMO); lithium nickel manganese cobalt oxide LiNi x Mn y Co z O 2 , wherein x+y+z=1 (NMC); lithium manganese iron phosphate LiFe x Mn y PO 4 , wherein x+y=1 (LMFP); and lithium-rich layered oxides Li 1+x TM 1-x O 2 , wherein TM is a blend of at least two transition metals (LRLO), in particular, wherein the transition metals are selected from the group consisting of Mn, Ni, and Co; and combinations thereof; and combinations thereof; ii) a conductive additive, and iii) a high voltage-stable catholyte comprising: - a lithium salt selected from the group consisting of LiTFSI, LiBOB, LiDFOB; LiBF 4 , LiFSI, LiClO 4 , and combinations thereof; - a polymer binder, wherein the polymer binder is a PVdF co-polymer; - a room temperature ionic liquid; - a plastic crystal selected from the group consisting of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, and mixtures thereof; and - optionally, a high boiling point solvent having a boiling point of at least 160 °C; wherein the positive electrode is characterized by having a density from 2.3 g/cm 3 to 3.6 g/cm 3 .
  2. The positive electrode according to claim 1, wherein the positive electrode has an active material loading from 0.5 mAh/cm 2 to 10 mAh/cm 2 .
  3. The positive electrode according to claims 1 or 2, wherein the PVdF co-polymer is selected from the group consisting of poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVdF-CTFE), poly(vinylidene fluoride-co-trifluoroethylene) (PVdF-TrFE), and mixtures thereof.
  4. The positive electrode according to any one of claims 1 to 3, wherein the polymer binder is in an amount from 1 wt% to 7 wt% of the total weight of the cathode; optionally, wherein the binder is PVdF-HFP.
  5. The positive electrode according to any one of claims 1 to 4, wherein the room temperature ionic liquid is selected from the group consisting of: 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI); 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide (PMI TFSI); 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide (DMPI TFSI); 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMI TFSI); 1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR 13 TFSI); 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR 14 TFSI); 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide (PP 13 TFSI); 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI-FSI); 1-methyl-3-propylimidazolium bis(fluorosulfonyl)imide (PMI FSI); 1,2-dimethyl-3-propylimidazolium bis(fluorosulfonyl)imide (DMPI FSI); 1-butyl-3-methylimidazolium bis(fluorosulfonyl)imide (BMI FSI); 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (PYR 13 FSI); 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide (PYR 14 FSI); 1-methyl-1-propylpiperidinium bis(fluorosulfonyl)imide (PP 13 FSI); and combinations thereof.
  6. The positive electrode according to claim 5, wherein the room temperature ionic liquid is PYR 14 TFSI.
  7. The positive electrode according to any one of claims 1 to 6, wherein the total amount of RTIL, plastic crystal, and, optionally, high boiling point solvent is from 1 wt% to 20 wt% of the total weight of the cathode.
  8. The positive electrode according to any one of claims 1 to 7, wherein the lithium salt comprises LiBOB, in particular, wherein the lithium salt is a mixture of LiBOB and LiTFSI, more particularly, wherein the lithium salt is LiBOB.
  9. The positive electrode according to any one of claims 1 to 8, wherein the electrolyte salt is in an amount from 1 wt% to 15 wt% of the total weight of the cathode.
  10. The positive electrode according to any one of claims 1 to 9, wherein the high voltage cathode active material is NMC, particularly a single crystal NMC.
  11. The positive electrode according to any one of claims 1 to 10, wherein the catholyte is in an amount from 5 wt% to 50 wt% with respect to the total weight of positive electrode; the high voltage cathode active material is in an amount from 50 wt% to 90 wt% of the total weight of the positive electrode; and the conductive additive is in an amount from 0.1 wt% to 5 wt% of the total weight of the positive electrode.
  12. A process for the preparation of a positive electrode as defined in any one of claims 1 to 11, the process comprising the following steps: i) providing a catholyte formulation comprising: the lithium salt, the polymer binder, the plastic crystal, the ionic liquid, and, optionally, the high boiling point solvent, in a suitable solvent; ii) adding under stirring to the catholyte liquid formulation of step (i) the high voltage cathode active material, the conductive additive and, optionally, an additional amount of the suitable solvent in order to obtain a positive electrode slurry; iii) casting the positive electrode slurry onto a positive electrode current collector and drying it in order to obtain a positive electrode; iv) calendering the positive electrode in order to obtain a calendered positive electrode; v) hot-pressing the calendered positive electrode in order to obtain the final positive electrode.
  13. A battery comprising: - a positive electrode as defined in any one of claims 1 to 11, - an anode, and - a solid electrolyte interposed between the positive electrode and the anode.
  14. The battery according to claim 13, wherein the solid electrolyte and the catholyte have the same composition.
  15. An article of manufacture comprising the battery as defined in claim 14.

Description

Technical Field The present disclosure relates to the field of solid-state lithium secondary batteries. In particular, it relates to a positive electrode comprising a cathode active material, a conductive additive, and a catholyte, as well to a process for its preparation, and to a solid-state lithium battery comprising said positive electrode. Background Art Solid-state batteries (SSB) based on solid electrolytes, using a lithium-metal anode and high voltage cathodes, can potentially provide higher energy density and safety than lithium ion batteries with liquid electrolytes based on highly flammable organic solvents. Composite positive electrodes for SSB typically comprise a cathode active material (CAM), a conductive additive such as carbon black, and a solid electrolyte (catholyte). To fulfil the requirements of high performance secondary batteries, the catholyte should have a high ionic conductivity, high chemical stability and wide electrochemical stability range. To provide sufficient ionic diffusion, positive electrode composites require a large catholyte fraction (30-50 vol%) and, consequently, the volume fraction of CAM of current SSB is relatively low, resulting in low energy density. Besides, the composite positive electrode should ideally have minimal void space and good CAM/catholyte contact, while including the minimum amount of catholyte needed to ensure sufficient transport of Li ions within the positive electrode structure. SSBs require the development of high loading (such as ca. ≥2-3 mAh/cm2), ideally, non-porous solid state positive electrodes to have an excellent electrical contact between the electrode components. The electrode components providing the electronic conductivity (conductive additive(s)) and the ionic conductivity (catholyte) are forming two parallel 3D networks in intimate contact between them and with the CAM. In addition, the catholyte, surrounding and contacting the CAM and the conductive additive, should be chemically and electrochemically stable and, therefore, should contain chemically compatible components which simultaneously should provide sufficient level of ionic conductivity and be stable to the electrooxidation under harsh testing conditions (≥4.2V versus Li/Li+ reference electrode, >40 °C, long time exposure, high surface area, high pressure, etc.) in the SSB environment. Although several SSB configurations have been disclosed in the available literature, stability of known catholytes (such as the ones containing polyethylene oxide (PEO)) in high voltage composite cathodes (for instance, containing lithium nickel manganese cobalt oxide (NMC) as CAM) is quite limited, especially at high temperature such as higher than 40°C. FR3 116 950 A1, KR 2021 0112925 A and US 2020/365944 A1 refer to positive electrode compositions for lithium secondary batteries, comprising a high voltage cathode active material, a conductive additive, and a catholyte comprising a lithium salt dissolved in an organic solvent or an ionic liquid. Therefore, there is still a strong need to improve the energy density and cyclability of solid-state batteries by achieving high loading composite positive electrodes while providing an improved stability at high voltages and enhanced electrochemical performance. Summary of Invention The inventors have developed a high-voltage positive electrode which allows reaching a high loading (ca. 3 mAh/cm2 or higher) suitable for solid state lithium-based batteries, the positive electrode being a composite comprising a high-voltage cathode active material, a conductive additive, and a catholyte, wherein the catholyte comprises a lithium salt, a specific polymer binder, and several types of plasticisers, these being (i) a room temperature ionic liquid (RTIL), (ii) a specific plastic crystal, and (iii), optionally, a high boiling point solvent. Advantageously, the positive electrode of the present disclosure has an improved electrochemical performance and, therefore, allows to improve the energy density and cyclability of lithium-based batteries, in particular, of lithium-metal solid state batteries. Thus, a first aspect of the invention relates to a positive electrode comprising: i) a high voltage cathode active material selected from lithium cobalt oxide LiCoO2 (LCO); high-voltage spinel LiNi0.5Mn1.5O4 (LNMO); lithium nickel manganese cobalt oxide LiNixMnyCo1-x-yO2, wherein x+y+z=1 (NMC); lithium manganese iron phosphate LiFexMnyPO4, wherein x+y=1 (LMFP); and lithium-rich layered oxides Li1+xTM1-xO2, wherein TM is a blend of at least two transition metals (LRLO), in particular, wherein the transition metals are selected from the group consisting of Mn, Ni, and Co; and combinations thereof;ii) a conductive additive, andiii) a high voltage-stable catholyte comprising: a lithium salt selected from the group consisting of LiTFSI, LiBOB, LiDFOB; LiBF4, LiFSI, LiClO4, and combinations thereof;a polymer binder, wherein the polymer binder is a PVdF co-polymer;a ro