Method for delithiating at least one lithium transition metal nitride

Abstract

The present invention relates to a method for delithiating at least one lithium transition metal nitride, the method comprising the following steps: a) mixing at least one oxidizing agent with said lithium transition metal nitride, and b) recovering the material obtained at the end of step a).

Description

[Technical field]

[0001] The present invention relates to a method for delithiating a particular material, a lithium transition metal nitride. The present invention also relates to the use of the material obtained by said method as an anode material for lithium ion batteries.

[0002] Traditionally, a lithium-ion battery comprises one or more positive electrodes, one or more negative electrodes, an electrolyte, and a separator.

[0003] Lithium-ion batteries are increasingly being used as autonomous energy sources, especially in applications related to electric mobility. This trend is explained in particular by their significantly higher gravitational and volumetric energy density than conventional nickel-cadmium (Ni-Cd) and nickel-metal hydride (Ni-MH) batteries, the absence of memory effect, their low self-discharge compared to other batteries, and the low cost per kilowatt-hour associated with this technology.

[0004] Lithium-ion batteries contain electrode active materials that can insert and remove lithium ions during charging and discharging processes, and these insertions and removals must be reversible so that the battery can store energy for several cycles.

[0005] Good mobility of the lithium ions in the structure and good electrical conductivity of the electrode materials are essential properties that allow these batteries to be used at high charge and discharge rates that allow high power. The specific power of the battery is an important issue for automotive applications, since it means that a lighter battery can be used for the same amount of work, and it also means that the battery can be used in safer conditions.

[0006] Rapid charging of lithium-ion batteries is also an important factor in the development of hybrid or other electric vehicles.

[0007] Currently, the cathode materials used in lithium-ion batteries are lithiated transition metal oxides, e.g., LiCoO2, LiNi 0.6 Mn 0.2 Co 0.2 The negative electrode material is an intercalation material, such as graphite or lithium titanate (Li4Ti5O 12 ).

[0008] During the charging process, the lithium-ion Li + is deintercalated from the positive electrode material and intercalated into the layers (in the case of graphite) or into crystallographic sites (in the case of lithium titanate) of the negative electrode material.

[0009] If the charging current is high and the potential of the negative electrode material is too low, there is a high probability of lithium depositing in the negative electrode, which can reduce the capacity of the battery cell and potentially lead to separator penetration and serious safety issues.

[0010] Lithium titanate has a high working potential (1.5 V vs Li) to avoid lithium precipitation. + / Li), it is an interesting material for high-power batteries. However, its capacity is still limited compared to that of graphite, which is more than twice the capacity of lithium titanate.

[0011] Nitride-based electrode materials have also been developed, particularly lithium transition metal nitrides, such as Li7MnN4 and Li3FeN2. These materials have roughly twice the capacity of lithium titanate and a working potential of 1.18 V for Li7MnN4 versus 1.2 V for Li3FeN2, respectively. + / Li, and 1.25V vs. Li for Li3FeN2. + / Li and has good high current performance.

[0012] These materials (Li7MnN4 and Li3FeN2) are described in US patent 5702843 as electrode materials for secondary batteries. The advantage of using these materials as electrode materials is that they allow direct application of available materials to electrodes. However, as shown in US patent 5702843, the working potential of these materials for use in cells is limited. Thus, their performance in cells is not satisfactory.

[0013] Thus, there remains a need to develop electrode materials that overcome the above-mentioned shortcomings.

[0014] It is therefore an object of the present invention to develop a method for delithiating lithium transition metal nitrides to obtain materials that can be used as anode active materials for lithium ion batteries.

[0015] Disclosure of the Invention The subject of the present invention is therefore a method for delithiating at least one lithium transition metal nitride, said method comprising the following steps: a) combining at least one oxidant with the lithium transition metal nitride; b) recovering the material obtained at the end of step a). It includes.

[0016] The method according to the invention makes it possible to obtain delithiated materials, which make it possible to avoid the initial discharge step customarily carried out in cells using materials commonly used in the prior art, such as materials of formula Li7MnN4 or Li3FeN2. Said materials according to the prior art are not delithiated materials, and therefore their use in cells requires an initial discharge step of the battery cell.

[0017] The subject of the invention is also the use of the material obtainable by the process according to the invention as anode active material for lithium-ion batteries.

[0018] Other advantages and features of the present invention will become more apparent by examining the detailed description and accompanying drawings. [Brief description of the drawings]

[0019] [Figure 1] 4 shows the diffraction diagram of the Li7MnN4 material and of the material obtained at the end of the method according to the invention. [Figure 2A] 1 is a scanning electron microscope image of the Li7MnN4 material. [Figure 2B] 2 is a scanning electron microscope image of the material obtained at the end of the method according to the invention. [Diagram 3] 1 is a graph showing the galvanostatic curve of a material obtained by the method according to the invention versus Li metal;

[0020] It should be noted that the expression "from to" as used in the present specification should be understood to include the respective extreme values ​​referred to.

[0021] The phrase "at least one" means one or more.

[0022] As mentioned above, according to step a) of the method according to the invention, at least one oxidizing agent is mixed with the lithium transition metal nitride.

[0023] Advantageously, the one or more transition metals are selected from Mn, Fe, Co, Ni, Cu and mixtures thereof.

[0024] The lithium transition metal nitrides have the formula Li7MnN4, Li3FeN2, Li 2.6 Co 0.4 N, Li 2.0 Ni 0.67 N, and Li 2.57 Cu 0.43 It is preferable that the material is selected from the group consisting of N materials.

[0025] More preferably, the lithium transition metal nitride is of formula Li7MnN4, or Li3FeN2.

[0026] The oxidizing agent is preferably chosen from the family of metallocenes in oxidized form.

[0027] The oxidizing agent is advantageously selected from cobaltocenium salts, preferably from cobaltocenium hexafluorophosphate, cobaltocenium tetrafluoroborate, bis(pentamethylcyclopentadienyl)cobalt hexafluorophosphate, bis(pentamethylcyclopentadienyl)cobalt tetrafluoroborate hexafluorophosphate, and mixtures thereof.

[0028] The oxidizing agent is more preferably selected from cobaltocenium hexafluorophosphate.

[0029] According to a preferred embodiment, the molar ratio between the oxidizing agent and the lithium transition metal nitride is in the range of 0.5-3, preferably in the range of 1-2.

[0030] In a preferred manner, step a) is carried out in the presence of at least one solvent.

[0031] The solvent is advantageously chosen from aprotic organic solvents, preferably chosen from acetonitrile, tetrahydrofuran, dimethylformamide, dichloromethane, ethyl acetate and mixtures thereof, preferably from acetonitrile.

[0032] According to another embodiment, solvents that can be used in lithium-ion battery electrolytes can also be used, preferably selected from ethylene carbonate (also referred to as "EC"), propylene carbonate (also referred to as "PC"), dimethyl carbonate (also referred to as "DMC"), diethyl carbonate (also referred to as "DEC"), ethyl methyl carbonate (also referred to as "EMC"), and mixtures thereof.

[0033] According to another embodiment, the solvent selected from an aprotic organic solvent (such as those described above) can be a mixture with a solvent that can be used in the electrolyte of a lithium-ion battery (such as those described above).

[0034] In a preferred manner, the solvent is acetonitrile.

[0035] As described above, according to step b) of the method according to the invention, the material obtained at the end of step a) is recovered.

[0036] Advantageously, this material can be recovered by centrifugation or by filtration.

[0037] Thereafter, this material can be rinsed with a solvent (preferably one selected from the aforementioned solvents), and it may be rinsed multiple times.

[0038] Thereafter, this material can be dried under vacuum.

[0039] In this way, materials of Li 7-x MnN4(0 < x ≦ 2) and Li 3-y FeN2(0 < y ≦ 1.2) can be obtained.

[0040] The subject of the present invention is also the use of the material obtained by the method according to the invention as a negative electrode active material for a lithium-ion battery.

[0041] As described above, the method according to the invention is a method for delithiation of at least one lithium transition metal nitride.

[0042] The protocol for delithiation of at least one lithium transition metal nitride can be described according to the following embodiments.

[0043] Advantageously, an oxidizing agent (such as those described above) can first be added to a solvent (such as those described above) to obtain a solution containing the oxidizing agent.

[0044] At this time, a lithium transition metal nitride (e.g., Li7MnN4 or Li3FeN2) can be added to the solution. The lithium transition metal nitride can be in powder form.

[0045] The amount of lithium transition metal nitride can be adjusted so that the molar ratio between the oxidizing agent and the lithium transition metal nitride is in the range of 0.5-3, preferably 1-2.

[0046] In this case, the lithium transition metal nitride can be mixed in the solution containing the oxidizing agent.

[0047] In this case, the temperature can be adjusted to a range of -5°C to 50°C.

[0048] All these steps can be carried out in a controlled environment, such as a glove box.

[0049] Advantageously, the oxidizing agent used may be a cobaltocenium salt. The color of the solvent may change during the reaction, indicating that the reaction is proceeding.

[0050] At the end of the reaction, the resulting material can be recovered.

[0051] Advantageously, the material can be separated from the solvent by centrifugation or filtration.

[0052] The material can then be rinsed multiple times with a solvent to remove undesired products, and then the material can be dried under vacuum.

[0053] The present invention will now be described in more detail with reference to examples which are not intended to limit the scope of the invention in any way, but rather to provide support for certain features, variants and preferred embodiments of the invention. EXAMPLES

[0054] Example 1: Method according to the invention Lithium transition metal nitride of formula Li7MnN4 is used.

[0055] As shown in Figure 1, a diffractogram is constructed of the pristine material (curve A, material A). The characteristic peaks of Li7MnN4 can be identified in this diffractogram.

[0056] Take a scanning electron microscope image of the material in its pristine state, as shown in Figure 2A (Material A).

[0057] The delithiation is carried out in a glove box at a temperature of 20° C. The molar ratio between the oxidant and the lithium transition metal nitride is 1.5.

[0058] Approximately 320 mg (0.002 mol) of Li7MnN4 was placed in an Erlenmeyer flask, followed by approximately 7.5 mL of acetonitrile and a bar magnet in the same Erlenmeyer flask. Approximately 1 g of cobaltocenium hexafluorophosphate (0.003 mol) was dissolved in 7.5 mL of acetonitrile to prepare an oxidizing solution. This oxidizing solution was added dropwise using an additional ampoule. A total of 15 mL of acetonitrile was used, resulting in a concentration of the oxidizing solution of 0.5 mol / L. Vigorous mixing was maintained overnight after addition to allow the oxidizing agent to react with the nitride.

[0059] The mixture was then decanted and transferred to a centrifuge tube. Centrifugation was performed in a centrifuge at a speed of 5000 rpm for 5 minutes. After centrifugation, the powder and the solution were separated.

[0060] A second approximately 5 mL of acetonitrile was introduced into the centrifuge tube to rinse, followed by a second centrifugation.

[0061] This rinsing and centrifugation step was repeated multiple times (3 times). Finally, the powder was placed in an oven (Buchi type) and dried under vacuum at 90° C. for 1 hour.

[0062] The delithiated material was obtained after drying.

[0063] Thus, at the end of the method according to the invention, a material is obtained.

[0064] The diffraction pattern of the obtained material was then prepared (curve B, material B), as shown in FIG.

[0065] A scanning electron microscope image of the material obtained by the method of the present invention was also taken (material B), as shown in FIG. 2B.

[0066] It is apparent that a material of formula Li7MnN4 has been modified.

[0067] More specifically, the formula Li 5.3 The material obtained was MnN4. 5.3 The presence of MnN4 material was confirmed by the lattice parameters (9.35 Å) calculated from the diffractogram.

[0068] Thus, delithiation of a material of formula Li7MnN4 has been achieved by the method according to the invention.

[0069] Example 2: Use of the material obtained in Example 1 in a half cell The active material obtained in Example 1 was prepared in the form of a composite electrode and tested with metallic lithium strips in a CR2032 button cell.

[0070] A composite electrode was prepared by mixing 70% by weight of the active material obtained in Example 1 with 22% by weight of acetylene black and 8% by weight of polytetrafluoroethylene (PTFE).

[0071] The separator used was a glass microfiber separator available from Whatman (CAT No. 1823-070®).

[0072] The electrolyte used was 1 mol / L lithium hexafluorophosphate dissolved in a mixture of carbonate solvents (ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1).

[0073] The half-cell was then assembled in a glove box.

[0074] Electrochemical Testing Galvanostatic cycling was performed using a BioLogic VMP3 potentiostat in a cycling regime of C / 20 (see FIG. 3). The potential window was between 1.6V and 0.9V.

[0075] 3, the starting point x=0 corresponds to the active material obtained at the end of Example 1. The potential at this point is E=1.7 V.

[0076] As x increases, the material is electrochemically depleted and the potential of the material decreases. It is known that when the potential is reduced to E=0.9V, the initial form of Li7MnN4 is obtained. In Figure 3, it can be seen that when E=0.9V, x is approximately equal to 1.7. In other words, when E=0.9V, approximately 1.7 lithium cells have been electrochemically reintercalated into the half cell. Thus, when x=0, the formula becomes Li 5.3 It can be determined that it is MNn4.

[0077] Thus, the material obtained by the method according to the invention has the formula Li 7-x MnN4 (where x=1.7) material, and thus the material is delithiated.

[0078] This material can be used as the active material for the negative electrode of a lithium battery.

Claims

1. 1. A method for delithiating at least one lithium transition metal nitride, comprising the steps of: a) mixing at least one oxidizing agent with the lithium transition metal nitride; b) recovering the material obtained at the end of step a). A method comprising:

2. the one or more transition metals are selected from Mn, Fe, Co, Ni, Cu and mixtures thereof; 2. The method of claim 1.

3. The lithium transition metal nitride has the formula Li ７ MnN ４ , Li ３ FeN ２ , Li ２．６ Co ０．４ N., Li. ２．０ Ni ０．６７ N, and Li ２．５７ Cu ０．４３ N materials, 3. The method according to claim 1 or 2.

4. The lithium transition metal nitride has the formula Li ７ MnN ４ or formula Li ３ FeN ２ It is of 3. The method according to claim 1 or 2.

5. the oxidizing agent is selected from cobaltocenium salts, preferably from cobaltocenium hexafluorophosphate, cobaltocenium tetrafluoroborate, bis(pentamethylcyclopentadienyl)cobalt hexafluorophosphate, bis(pentamethylcyclopentadienyl)cobalt tetrafluoroborate hexafluorophosphate, and mixtures thereof; 3. The method according to claim 1 or 2.

6. the molar ratio of the oxidizing agent to the lithium transition metal nitride is in the range of 0.5 to 3, preferably in the range of 1 to 2; 3. The method according to claim 1 or 2.

7. Step a) is carried out in the presence of at least one solvent, 3. The method according to claim 1 or 2.

8. the solvent is selected from aprotic organic solvents, preferably from acetonitrile, tetrahydrofuran, dimethylformamide, dichloromethane, ethyl acetate, and mixtures thereof, preferably from acetonitrile; 8. The method according to claim 7.

9. the solvent is selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and mixtures thereof; 8. The method according to claim 7.

10. 3. Use of the material obtained by the method according to claim 1 or 2 as an active material for the negative electrode of a lithium ion battery.

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