Search

EP-4736246-A1 - ELECTROCHEMICAL ELEMENT COMPRISING A POSITIVE ELECTRODE BASED ON LITHIUM MANGANESE IRON PHOSPHATE

EP4736246A1EP 4736246 A1EP4736246 A1EP 4736246A1EP-4736246-A1

Abstract

The invention relates to a lithium-ion electrochemical element comprising: - a positive electrode comprising one or more positive active materials, one of them being a lithium manganese iron phosphate, - a negative electrode comprising one or more negative active materials, one of them being a composite of silicon and carbon, - an electrolyte comprising a mixture of solvents and one or more lithium salts dissolved in the mixture of solvents, the mixture of solvents comprising at least one fluorinated cyclic carbonate, the other solvent(s) being chosen from non-fluorinated cyclic carbonates or non-fluorinated linear carbonates, the volume proportion of fluorinated cyclic carbonate representing from 10% to 30% of the total volume of the solvents, at least one lithium salt being lithium bis(fluorosulfonyl)imide Li(FSO 2 ) 2 N.

Inventors

  • MORTEMARD DE BOISSE, Benoît
  • GAJAN, Antonin
  • Tessier, Cécile

Assignees

  • SAFT

Dates

Publication Date
20260506
Application Date
20240612

Claims (14)

  1. [Claim 1] Lithium-ion electrochemical element comprising: - a positive electrode comprising one or more positive active materials, one of which is a lithium manganese iron phosphate of formula LixMni-y-zFe y MzPO4 (LMFP) where 0.8<x<1.2;0.50<1-yz<1; 0<y+z<0.50; 0<y<0.50; 0<z<0.2; M being one or more elements selected from the group consisting of Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Ni, Zn, Y, Zr, Nb, W, Pb, Mo and S, - a negative electrode comprising one or more negative active materials, one of which is a composite of silicon and carbon, - an electrolyte comprising a mixture of solvents and one or more lithium salts dissolved in the mixture of solvents, the mixture of solvents comprising at least one fluorinated cyclic carbonate, the other solvent(s) being chosen from non-fluorinated cyclic carbonates or non-fluorinated linear carbonates, the volume proportion of fluorinated cyclic carbonate representing from 10 to 30% of the total volume of the solvents, at least one lithium salt being lithium bis(fluorosulfonyl)imide Li(FSC>2)2N (LiFSI).
  2. [Claim 2] An electrochemical element according to claim 1, wherein the silicon-carbon composite consists of a carbon matrix in which silicon particles are incorporated, the largest dimension of the silicon particles being less than or equal to 500 nm.
  3. [Claim 3] An electrochemical element according to claim 1, wherein the silicon-carbon composite consists of a porous carbon matrix, silicon particles partially or completely covering the surface of the pores of the carbon matrix, the diameter of the pores of the carbon matrix ranging from 10 nm to 1 pm.
  4. [Claim 4] An electrochemical element according to claim 3, wherein the porous carbon matrix consists of carbon particles, the pores of the porous carbon matrix representing from 15 to 90% of the volume of the carbon particles, the volume of the carbon particles being delimited by the outer surface of the particles.
  5. [Claim 5] An electrochemical element according to one of the preceding claims, wherein the negative electrode further comprises a second active material in graphite, graphite representing 10 to 90% of the total mass of the active materials of the negative electrode, silicon and carbon composite representing 90 to 10% of the total mass of the active materials of the negative electrode.
  6. [Claim 6] Electrochemical element according to one of the preceding claims, in which the fluorinated cyclic carbonate is ethylene fluorocarbonate (FEC).
  7. [Claim 7] An electrochemical element according to any preceding claim, wherein the solvent mixture comprises from 1 to 20% by volume of non-fluorinated cyclic carbonate.
  8. [Claim 8] An electrochemical element according to any preceding claim, wherein the solvent mixture consists of ethylene fluorocarbonate (FEC), ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC).
  9. [Claim 9] An electrochemical element according to claim 8, wherein the volume proportions of FEC, EC, DMC and EMC are within the following respective ranges: 15-25%, 5-15%, 40-50% and 20-30%.
  10. [Claim 10] Electrochemical element according to one of the preceding claims, in which the lithium ions from the lithium bis(fluorosulfonyl)imide salt Li(FSC>2)2N (LiFSI) represent from 50 to 99%, preferably from 90 to 99% of the total lithium ions provided by the lithium salts.
  11. [Claim 11] Electrochemical element according to one of the preceding claims, in which the lithium bis(fluorosulfonyl)imide salt Li(FSC>2)2N (LiFSI) is associated with at least one other salt chosen from lithium hexafluorophosphate LiPFe, lithium tetrafluoroborate UBF4 and lithium difluoro(oxalato)borate (LIDFOB).
  12. [Claim 12] Electrochemical element according to one of claims 1 to 9, in which the lithium bis(fluorosulfonyl)imide salt Li(FSC>2)2N (LiFSI) is the only lithium salt of the electrolyte.
  13. [Claim 13] Electrochemical element according to one of claims 1 to 12, in which the total concentration of lithium ions provided by the lithium salt(s) ranges from 0.9 to 1.3 moles of lithium per liter of solvent(s).
  14. [Claim 14] Electrochemical element according to one of the preceding claims, in which the positive electrode further comprises one or more positive active materials chosen from: a) a lithium oxide of nickel, manganese and cobalt of formula Liw(NixMn y COzMt)O2 (NMC) where 0.9<w<1.1;0<x<1;0<y<1;0<z<1;0<t<1; M being selected from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La and mixtures thereof, b) a lithium oxide of nickel, cobalt and aluminium of formula Li w (Ni x Co y Al z Mt)O2 (NCA) where 0.9<w<1.1;0<x<1;0<y<1;0<z<1;0<t<1; M being selected from the group consisting of B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ga, Ta, Nd, Pr, La and mixtures thereof, c) a compound of formula Lii + xMi. x O2-yFy of cubic crystal structure where M represents at least one element selected from the group consisting of Na, K, Mg, Ca, B, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Y, Zr, Nb, Mo, Ru, Ag, Sn, Sb, Ta, W, Bi, La, Pr, Eu, Nd and Sm and where 0 < x < 0.5 and 0 < y < 1, d) a lithium nickel manganese oxide (NMX) of formula Lia(Nii-xy-zMn x COyMz)O2 with 0.9<a<1.1;0.60<1-xyz<0.80;0<x<1; 0<y<0.02;0<z<1; and M being selected from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ga, Ta, Nd, Pr, La and mixtures thereof; e) a lithium nickel manganese oxide of the formula Liw(Ni x Mn y CozMt)O2 where 1.1 <w<1.6;0<x<1;0.50<y<0.80;0<z<0.02;0<t<1; M being selected from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La and mixtures thereof.

Description

Description Title: Electrochemical element comprising a positive electrode based on lithium manganese and iron phosphate Technical field of the invention [0001] The technical field of the present invention is that of electrochemical elements comprising a positive electrode based on lithium manganese and iron phosphate. Background of the invention [0002] Rechargeable lithium-ion electrochemical cells are widely used as energy storage devices to power portable electronic devices such as laptops, cell phones or to power electric or hybrid vehicles. [0003] Electrochemical elements comprising a positive electrode whose active material is a lamellar lithium oxide and comprising a negative electrode whose active material is graphite are known from the state of the art. They have a high specific energy but they can prove unstable when subjected to an overload or overheating. This is why attempts have been made to improve their safety of use in the event of overload or overheating. For example, it has been proposed to replace part of a lithium oxide of nickel, manganese and cobalt with a lithium manganese phosphate LiMnPCL or a lithium iron phosphate LiFePCL, or with a lithium manganese and iron phosphate LiMni. x Fe x PO4 with x<1 (LMFP). Document WO 2016/184896 describes such an element. The electrochemical element resulting from this partial replacement has satisfactory safety of use. However, the increase in safety of use is obtained at the expense of the specific energy of the element. By increasing the ratio between the amount of lithium phosphate and the amount of lithium nickel manganese cobalt oxide, an element is obtained which has satisfactory safety of use, but whose specific energy does not reach that of an element whose positive electrode contains a lithium nickel manganese cobalt oxide as the only active material. [0004] Figure 1a compares the specific energies of different elements 1-3 of the prior art. These differ in the composition of their positive electrode. The negative electrode of elements 1-3 is made of graphite. Element 1 comprising a positive electrode based on a lithium oxide of nickel, manganese and cobalt of formula LiNio,8Mno,iCoo,iC>2 (NMC811) has a specific energy of more than 300 Wh/kg, which is high, but this cell has insufficient safety of use in case of overheating or overload. Cell 2 comprising a positive electrode based on a lithium manganese and iron phosphate has a specific energy of only 240 Wh/kg and satisfactory safety of use. Cell 3 whose positive electrode comprises a mixture of a lithium manganese and iron phosphate and a lithium nickel manganese and cobalt oxide of formula NMC811 has satisfactory safety of use but a specific energy lower than that of cell 1. [0005] Figure 1b is a comparison of the volume energies of the three elements 1, 2 and 3 of the prior art. It can be seen that the volume energies of these three elements are in the same order as that of the mass energies of Figure 1a. [0006] It is therefore sought to improve the mass energy and/or the volume energy of an element whose positive electrode contains a mixture of LMFP and a lamellar lithium oxide and whose negative electrode contains graphite, while maintaining satisfactory safety for the user. Preferably, it is desired that the improvement of the mass energy and/or the volume energy does not occur at the expense of the performance of the element during cycling. Summary of the invention [0007] To this end, the present invention provides a lithium-ion electrochemical element comprising: - a positive electrode comprising one or more positive active materials, one of which is a lithium manganese iron phosphate of formula LixMni.y. z Fe y M z PO4 (LMFP) where 0.8<x<1.2;0.50<1-yz<1;0<y+z<0.50;0<y<0.5;0<z<0.2; M being one or more elements selected from the group consisting of Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Ni, Zn, Y, Zr, Nb, W, Mo, Pb and S, - a negative electrode comprising one or more negative active materials, one of which is a composite of silicon and carbon, - an electrolyte comprising a mixture of solvents and one or more lithium salts dissolved in the mixture of solvents, the mixture of solvents comprising at least one fluorinated cyclic carbonate, the other solvent(s) being chosen from non-fluorinated cyclic carbonates or non-fluorinated linear carbonates, the volume proportion of fluorinated cyclic carbonate representing from 10 to 30% of the total volume of the solvents, at least one lithium salt being lithium bis(fluorosulfonyl)imide Li(FSO2)2N (LiFSI). [0008] The invention is based on the discovery that three specific constituents of the element cooperate with each other to improve on the one hand the mass energy and/or the volume energy without excessively penalizing the cycling performance of the element. These three constituents are the electrolyte, the negative active material and the positive active material, as described above. The invention makes it possible, for example, to in