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EP-4736247-A1 - POSITIVE ELECTRODE COMPOSITION

EP4736247A1EP 4736247 A1EP4736247 A1EP 4736247A1EP-4736247-A1

Abstract

The present invention relates to an NVPF-based composition and to its use in the field of batteries as electrochemically active material. It also relates to a conductive composition comprising said composition and to a process for obtaining said composition.

Inventors

  • GAFFURI, Pierre
  • DUFOUR, Marion
  • LECLERCQ, Florent
  • BERTRY, Laure

Assignees

  • SPECIALTY OPERATIONS FRANCE

Dates

Publication Date
20260506
Application Date
20240627

Claims (14)

  1. 1. A process for the preparation of a composition comprising particles of NVPF material of formula Na3V2(PO4)2F3, which is optionally partially oxidized, as well as carbon, comprising the following steps: a) providing a mixture of VPO4 and sodium fluoride; b) introducing the mixture of step a) next to an oxygen-comprising hydrocarbon compound, which thermally decomposes to give carbon, in a container and closing the container so as to obtain a confined reaction medium; c) heating the reaction medium of step b) up to a temperature ranging from 700°C to 900°C and maintaining this temperature for a time ranging from 0.5h to 6h so as to form concomitantly NVPF and carbon to arrive to the desired composition, wherein carbon is introduced in said composition by chemical vapor deposition.
  2. 2. A process for the preparation of a composition comprising particles of NVPF material of formula Na3V2(PO4)2F3, which is optionally partially oxidized, as well as carbon, comprising the following steps: a') introducing NVPF next to an oxygen-comprising hydrocarbon compound in a container and closing the container so as to obtain a confined reaction medium; b’) heating the reaction medium of step a’) up to a temperature ranging from 700°C to 900°C and maintaining this temperature for a time ranging from 0.5h to 6h so as to arrive to the desired composition, wherein carbon is introduced in said composition by chemical vapor deposition.
  3. 3. A composition comprising particles of NVPF material of formula Na3V2(PO4)2F3, which is optionally partially oxidized, as well as carbon, characterized by : (1 ) a carbon content of between 0.17% and 3.0%, this content being expressed by weight of the element carbon with respect to the total weight of the composition, (2) an electronic conductivity at 22°C o expressed in mS/cm such as o > 4.3717 x +0.2186 with x being the carbon content expressed in % by weight with respect to the total weight of the composition; wherein the electronic conductivity o is measured on a sample of said composition pressed at 4.75 MPa by a Direct Current (DC) method.
  4. 4. The composition as claimed in claim 3, in which the proportion by weight of NVPF, which is optionally partially oxidized, is between 92.0% and 99.83% by weight, this proportion being expressed with respect to the total weight of the composition.
  5. 5. The composition as claimed in one of claims 3 to 4, in which the unit cell parameter c is greater than or equal to 10.686 angstroms, indeed even greater than or equal to 10.750 angstroms.
  6. 6. The composition as claimed in one of claims 3 to 5, in which the unit cell volume V is between 872.604 and 878.390 angstroms 3 .
  7. 7. The composition as claimed in one of claims 3 to 6, exhibiting a ratio R of less than or equal to 1.1 , preferably of less than or equal to 1.0, indeed even of less than or equal to 0.9, in which: - R denotes the arithmetic mean of the ratio ID/IG calculated over at least 6 measurements carried out at various points of a sample of the composition; - ID denotes the intensity of the Raman vibration band centered around 1340 cm -1 ; - IG denotes the intensity of the Raman vibration band centered around 1590 cm’ 1 .
  8. 8. The composition as claimed in one of claims 3 to 7, in which the tapped density is greater than or equal to 0.9 g/ml and less than or equal to 2.0 g/ml.
  9. 9. The use of the composition as claimed in one of claims 3 to 8 as electrochemically active material of electrodes for sodium-ion batteries.
  10. 10. A conductive composition comprising the composition as claimed in one of claims 3 to 8, at least one electron-conducting material and optionally a binder.
  11. 11. The conductive composition as claimed in claim 10, in which the electronconducting material is chosen from carbon fibers, carbon black, carbon nanotubes, graphene and their analogs.
  12. 12. The conductive composition as claimed in claim 10 or 11 , in which the binder is chosen from polytetrafluoroethylene, polyvinylidene fluoride or a copolymer of vinylidene fluoride and of at least one comonomer, such as, for example, hexafluoropropylene, polymers derived from carboxymethylcellulose, polysaccharides and latexes, in particular of styrene/butadiene rubber type.
  13. 13. A positive electrode comprising a conductive composition as claimed in one of claims 10 to 12 or a composition as claimed in one of claims 3 to 8.
  14. 14. A sodium-ion battery comprising the positive electrode of claim 13.

Description

POSITIVE ELECTRODE COMPOSITION This application claims priority to European patent application No. 23306118.3 filed on June 30, 2023, the whole content of this application being incorporated herein by reference for all purposes. The present invention relates to an NVPF-based composition and to its use in the field of batteries as electrochemically active material. It also relates to a conductive composition comprising said composition and to a process for obtaining said composition. [Technical background] The demand for lithium-ion batteries has increased in recent years with regard to their application in a wide variety of electronic devices, such as portable telephones and electric vehicles. In point of fact, lithium-based compounds are relatively expensive and natural lithium sources are unequally distributed over the planet and are not readily accessible as they are localized in a small number of countries. Alternatives to this element have thus been sought. To this end, sodium- ion batteries have been developed. This is because sodium is very abundant and distributed homogeneously, and is advantageously nontoxic and economically more advantageous. However, the redox potential of the Na+/Na couple is (-2.71 V vs SHE) and is thus greater than that of the Li+/Li couple (-3.05 V vs SHE), for a triple molar mass. These specificities make it difficult to choose a host material. In this context, the material Na3V2(PO4)2F3 (or NVPF) has proved to be a particularly advantageous electrochemically active material with regard to its electrochemical performance qualities. Indeed, NVPF usually shows a reversible capacity of more than 120 mAh/g and exhibits good cycling performance at room temperature. To be used as a cathode active material (CAM), NVPF composition has to possess not only high ionic conductivity but also good electronic conductivity in order to efficiently drain electrons towards the current collector during working of the battery. If both criteria are gathered then high power density can be achieved. For this purpose, NVPF particles are generally coated with conductive materials. The conductive material can be of different nature and should not be involved in the electrochemical process contributing to the cycling of the battery. Moreover, the conductive material has to be present in a moderate content in order to maximize the content of pure cathode active material and thus to maximize the energy density of the electrode. Generally carbon is preferred to play the role of electron conductor while keeping the electrochemical properties of NVPF unchanged. US2018/0297847 describes NVPF particles obtained through exposing under an inert atmosphere, a mixture of VPO4 material with an effective amount of sodium fluoride NaF and at least one hydrocarbon- and oxygen- containing compound which is a source of elementary carbon, to temperature conditions that are favourable for calcining said mixture so as to form NasV2(PO4)2F3 compound e.g. 800°C during one hour. Cellulose is used as source of carbon. The carbon coating represents 0.5% to 5.0% by weight of the total weight of the material. US2021/0305549 relates to a NVPF-based composition comprising particles of NVPF as well as carbon in graphitized form. The composition is obtained through calcination at 800°C of an intimate mixture of VPO4, NaF and cellulose as source of carbon. The carbon content represents between 1 .0% to 3.5% by weight of the total weight of the composition. The Applicant has experienced that NVPF-based composition prepared from calcination of intimate mixtures of VPO4, NaF and at least one hydrocarbon- and oxygen- containing compound as source of elementary carbon (namely cellulose), leads to coated NVPF with only moderate electronic conductivity when keeping a reasonable carbon amount to maintain energy density. Chemical vapor deposition (CVD) which is generally admitted to be an efficient route to prepare highly conductive carbon, is sometimes used to deposit carbon material onto electrochemically active material for electrode application. For example, Y.Fang et Al., disclose in Advanced Materials, 2015, 27, 5895-5900, chemical vapor deposition of conductive carbon onto NasV2(PO4)3 (NVP). For this purpose NVP material is introduced in a CVD furnace where acetylene gas pyrolysis is conducted to generate conductive carbon structure. Acetylene, in mixture with argon, is introduced into the furnace while the furnace temperature is increased to 690°C. The decomposition of acetylene leads to carbon deposition on the surface of NVP. Similarly, Y.Zhang et Al., disclose in Journal of Materials Chemistry , 2018, 6, 4525-4534, the chemical vapor deposition of conductive carbon onto Na3V2(PO4)2F3 (or NVPF) . For this purpose NVPF material is introduced in a CVD furnace where acetylene gas pyrolysis is conducted to generate conductive carbon structure. A flow of acetylene, in mixture with argon, is introduced into the furnace while the furna