EP3386921A1

EP3386921A1 - Cathode material for li-ion batteries

Info

Publication number: EP3386921A1
Application number: EP16819337.3A
Authority: EP
Inventors: Jean-François COLIN; Carole Bourbon; Quentin JACQUET
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2015-12-09
Filing date: 2016-11-29
Publication date: 2018-10-17
Also published as: US10644313B2; JP2019504437A; JP6861208B2; FR3045211A1; WO2017098113A1; US20180331359A1; FR3045211B1

Abstract

The present invention relates to an electrode material of formula Li_2+xNi_uTi_vNb_wO₄, in which: 0 < x < 0.3, u > 0 and w > 0, x+u+v+w = 2, x+2u+4v+5w = 6; the electrode material having a disordered crystalline NaCl structure. The present invention likewise relates to the cathode having said material as electronically active material, but also to the lithium-ion battery containing said cathode.

Description

CATHODE MATERIAL FOR BATTERIES Ll-ION

FIELD OF THE INVENTION The invention relates to a lithium-based material of the formula Li _{2 + x} Ni _u Ti _v Nb _w 0 ₄ , as well as its use as a cathode material and its method of preparation.

The field of use of the present invention relates to the storage of electrical energy, and more particularly to lithium-ion batteries.

PRIOR STATE OF THE TECHNIQUE

Lithium-ion batteries are particularly suitable for portable electronic equipment with regard to their energy density and their stability over time in terms of charging and discharging cycles.

A lithium-ion battery typically includes the following assembly:

a positive electrode (cathode) comprising a lithium-based material, a lithium salt-based electrolyte

a negative electrode (anode), generally based on carbon, for example graphite.

The reversible exchanges of Li ⁺ ions between the cathode and the anode ensure its operation. At the cathode, the materials with the highest energy are the lithium super-stoichiometric lamellar oxides. They make it possible to reach suitable specific capacities (250mAh / g). However, they have many disadvantages mainly related to the participation of oxygen in the electrochemical processes, among which:

a strong irreversible in the first cycle;

- structural instability;

a loss of potential in cycling.

To remedy these problems. It has been envisaged to use materials of Rock-Salt structures (of the NaCl type), for example:

the document WO 2009/120156 discloses the Li ₂ FeTiO _{4 material} having a capacity of 130 mAh / g at C / 20 and 60 ° C between 3.9V and 1.9V, CN 104269520 discloses the Li ₂ FeTiO _{4 material} having a graphite coating and a capacity of 200 mAh / g at C / 30 between 5V and 1.5V,

JP 2013-206746 discloses the material Li ₂ NiSii_ _x Ti _x 0 ₄ with 0 <x <l whose capacity is 120 mAh / g at C / 20 between 4V and 2V,

the document WO 2014/73700 describes the material Li ₂ Ni ₍ i _{x x} y ₎ Co _x Mn _y Ti0 ₄ with x> 0, y> 0, whose capacity is 230 mAh / g at C / 100 between 4.8V and 2V .

But, even if the Li ₂ NiTiO _{4 materials} of disordered NaCl structure have a high theoretical capacity (290 mAh / g), based on the oxidation of Ni ²⁺ to Ni ⁴⁺ only, these materials have an ionic conductivity that is too low , thus limiting the performance of the material.

The Applicant has developed a novel lithiated material having an ionic conductivity greater than that of Li ₂ NiTiO ₄ type materials and a theoretical specific capacity that can reach or exceed 250 mAh / g.

SUMMARY OF THE INVENTION

The present invention relates to an electrode material of formula Li _{2 + x} Ni _u Ti _v Nb _w 0 ₄ in which:

0 <x <0.3,

u> 0 and w> 0,

x + u + v + w = 2,

x + 2u + 4v + 5w = 6.

In this formula, u and w are different from 0. On the other hand, v can be equal to 0; in this case, the titanium is completely substituted by nickel and niobium.

Advantageously, the formula above comprises at least one of the following parameters:

u can be between 0.9 and 4/3.

v can be between 0 and 0.6.

w can be between 0.3 and 0.77. The material of formula Li _{2 + x} Ni _u Ti _v Nb _w 04 is particularly suitable for use as a cathode material, in particular in a lithium-ion battery.

In general, this material has a disordered NaCl crystal structure.

An NaCl-type structure corresponds to two cubic face-centered subnetworks (atoms distributed at the 8 vertices of a cube and in the center of each face of this cube). These two subnets are offset by half the mesh side.

A disordered structure corresponds to a crystal whose atoms are regularly placed in the sites, but whose distribution of atoms is irregular.

As already indicated, the material according to the invention has a theoretical specific capacity that can reach or exceed 250 mAh / g without involving an electrochemical activity of the oxygen of the network thanks to the Ni ²⁺ / Ni ⁴⁺ pair. In addition, the substitution of titanium by lithium and by a metal (nickel and / or niobium) makes it possible to improve its ionic conductivity properties and therefore its performance. In general, the lithium enriched lamellar oxides make it possible to obtain high capacities because a part of the oxygen of which they are constituted participates in the electrochemical reaction by oxidizing the charge, such as metals, which creates a structural instability. . The material according to the invention makes it possible to reach 250mAh / g without the oxygen of the structure being oxidized, since the Ni ²⁺ / Ni ⁴⁺ pair provides enough electrons.

The material according to the invention may be chosen from the group comprising: Li ₂ .iNiTio. ₆ Nbo.304; Lizo5NiTio.8Nbo.15O4; and Li ₂ . ₂ NiTio. ₂ Nb ₀ .60 ₄ . By way of example of material according to the invention:

Li ₂ . ₂ NiTio. ₂ Nbo.604 (x = 0.2, u = 1, v = 0.2, w = 0.6) has a theoretical capacity, without oxygen intervention, of 263 mAh / g.

Liz1NiTio.6Nbo.3O4 (x = 0.1, u = 1, v = 0.6, w = 0.3) has a theoretical capacity, without oxygen intervention, of 276 mAh / g. In general, the theoretical specific specific capacity of the material according to the invention may be between 240 and 285 mAh / g.

The material according to the invention has an ionic conductivity higher than that of conventional Li ₂ NiTiO ₄ type materials, thanks to the increase in the number of percolation paths for lithium. Since lithium is the only mobile ion in the structure, it can only diffuse if one of the neighboring sites is also occupied by a lithium ion. The increase of the lithium / metal ratio makes it possible to increase the probability of occurrence of this configuration and thus to multiply the possible percolation paths.

The material according to the invention may be in the form of particles or agglomerates of particles. Advantageously, it is formed of agglomerates of 1 to 5 microns made of particles. The particles are preferentially spherical. Their average diameter is advantageously between 30 and 100 nanometers.

The present invention also relates to the process for manufacturing the material of formula Li _{2 + x} Ni _u Ti _v Nb _w 04.

It may especially be a solid, sol-gel or hydrothermal synthesis, or melted (molten salts) synthesis. Advantageously, it is carried out by molten salt. These synthetic techniques are part of the general knowledge of those skilled in the art and do not require special conditions.

By way of example, the synthesis can be carried out by melted salts from precursors of lithium, nickel, titanium and niobium in a mixture of NaCl / KCl salts.

The precursors used in this case can in particular be Li ₂ CO ₃ , Ni (CH ₃ COO) ₂ . 4H ₂ O, TiO ₂ and Nb ₂ O ₅ .

The present invention also relates to a cathode in which the electronically active material is the material, described above, of formula Li _{2 + x} Ni _u Ti _v Nb _w 0 ₄ . The present invention also relates to a lithium-ion battery (or accumulator) comprising this cathode.

This lithium-ion battery comprises in particular the assembly of a cathode according to the invention, an electrolyte based on lithium salt and an anode, generally based on carbon (for example graphite).

The person skilled in the art will know how to prepare this battery by using his general knowledge to implement conventional techniques, in particular by depositing an ink comprising the material Li _{2 + x} Ni _u Ti _v Nb _w 0 ₄ .

The invention and the advantages thereof will appear more clearly from the following figures and examples given to illustrate the invention and not in a limiting manner. DESCRIPTION OF THE FIGURES

Figure 1 illustrates the diffractograms of the compounds Li _{2 + x} NiTii _4x Nb 3 _X 04, with x = 0.05, 0.10, 0.20.

Figure 2 corresponds to an enlargement of the diffractograms of the compounds Li _{2 + x} NiTii _4x Nb ₃ × 04 (x = 0.05, 0.10, 0.20) between 30 and 50 ° C.

FIG. 3 illustrates the charging and discharging capacity of Li ₂ NiTiO _{4 material} as a function of the number of cycles.

Figure 4 illustrates the charging and discharging capacity of the material Li _2i iNiTio _i6 Nbo, ₄ depending on the number of cycles.

FIG. 5 illustrates the voltage of Li ₂ NiTiO _{4 material} as a function of the specific capacitance.

Figure 6 illustrates the voltage of Li _2i material iNiTio, ₆ Nbo, ₃ 0 ₄ depending on the specific capacity.

FIG. 7 illustrates the potential as a function of the load capacity of materials Li _{2 + x} NiTii_ _4x Nb _3x 0 ₄ (x = 0.05, 0.10, 0.20).

Figure 8 shows an image obtained by scanning electron microscope of NiTi material Li ₂ _0, 6Nbo, ₃ 0 _4. EXAMPLES OF CARRYING OUT THE INVENTION

Synthesis The Li _{2 + x} NiTii 4 _X Nb 3 _X 04 materials (x = 0.05, 0.10, 0.20) were synthesized in the molten salt route according to the following protocol, under air.

The precursors Li ₂ CO ₃ , Ni (CH ₃ COO) ₂ . 4H ₂ O, TiO ₂ and Nb ₂ O ₅ are added in stoichiometric proportions to a eutectic mixture NaCl / KCl (4e mol).

After mixing, the mixture is heated at 350 ° C. for 2 hours and then at 670 ° C. for 3 hours.

After cooling, the material is washed with distilled water to remove the salt mixture and then dried at 80 ° C. in air.

The diffractograms of FIGS. 1 and 2 show the different phases substituted for Nb, showing a linear evolution of the mesh parameters, which indicates that the substitution results in a solid solution.

Electrochemical tests a) Preparation of the positive electrode The active material of formula Li _{2 + x} NiTii 4 _X Nb ₃ × 04 (x = 0.05, 0.10, 0.20) is mixed with 80% by mass with carbon black (Super P carbon, 10%) and PVDF binder (10% polyvinylidene fluoride) dissolved in N-methyl-2-pyrrolidone.

This mixture is then coated on an aluminum foil (100 micrometers) and then dried at 60 ° C. b) Assembly of the accumulator

The electrode thus produced is introduced into a cell type "button cell" format 2032. The negative electrode is made of lithium metal. Two types of separators are used: a polypropylene film (Celgard 2400) and a polyolefin film (Viledon ^® ).

The electrolyte used is a compound of ethylene carbonate, propylene carbonate, dimethyl carbonate and lithium hexafluorophosphate (LiPF ₆ ) (Electrolyte LP100). c) Galvanostatic Cycling At room temperature, a current is imposed on the system in order to obtain a C / 50 regime, that is to say the extraction / insertion of a lithium ion in 50 hours. d) Results FIGS. 3 and 4 show that the substitution of titanium by lithium and niobium results in a higher capacity (80 mAh / g vs. 91 mAh / g) and is more stable during the C / 50 cycling between 4.8V and 2 V (Figures 5 and 6).

This improvement is attributed to a better ionic conductivity of the material because the polarization decreases with the substitution.

Figure 7 corresponds to the potential as a function of the load capacity. It highlights the importance of the substitution of titanium atoms by lithium and niobium atoms. The higher the substitution rate, the higher the capacity achievable in the first load. For the highest substitution rate (x = 0.2), 87% of the theoretical capacity is reached at room temperature and 95% at 55 ° C.

Figure 8 corresponds to an image obtained by scanning electron microscope of Li ₂ material, iNiTio _i6 Nbo, 304. It illustrates the presence of agglomerates of globally spherical particles.

Claims

1. An electrode material of formula Li ₂ + _x Ni _u Ti _v Nb _w 04 in which:

0 <x <0.3,

u> 0 and w> 0,

x + u + v + w = 2,

x + 2u + 4v + 5w = 6,

the electrode material having a disordered NaCl crystal structure.

Electrode material according to claim 1, characterized in that u is between 0.9 and 4/3.

Electrode material according to claim 1 or 2, characterized in that v is between 0 and 0.6.

Electrode material according to one of Claims 1 to 3, characterized in that w is between 0.3 and 0.77.

Electrode material according to one of claims 1, 2 or 4, characterized in that it is selected from the group consisting of: Li ₂ .iNiTi ₀ . ₆ Nbo.304; Lizo5NiTio.8Nbo.15O4; and Li ₂ . ₂ NiTi ₀ . ₂ Nb ₀ .6O ₄ .

Electrode material according to one of claims 1 to 5, characterized in that it is formed of agglomerates of 1 to 5 micrometers consisting of particles whose average diameter is between 30 and 100 nanometers.

Cathode having as electronically active material the material of one of claims 1 to 6.

Lithium-ion battery containing the cathode object of claim 7.

Process for the preparation of the material according to one of Claims 1 to 6, characterized in that it is carried out by molten salt route.