FR2981799A1 - NEW CATHODIC MATERIAL FOR LITHIUM BATTERY - Google Patents

Abstract

The present invention relates to a novel active cathode material comprising a composition of the following formula: Li VO where x represents a number such that 0 <= X <= 1 and where y represents a number such that 0 <= y <= 0.1 for batteries at lithium, its manufacturing process, as well as its uses.

Description

The present invention relates to a new cathode material for lithium batteries, its manufacturing process, as well as its uses. The storage of energy is one of the central issues of energy saving. Indeed, it is important to be able to store and / or transport energy with a minimum of losses, and to obtain a rechargeable energy storage material having a substantial lifetime. Lithium batteries or batteries are nowadays an element of answer to this problem of storage of energy. These constitute the largest share of the portable battery market. They are especially used in laptops, cell phones, cameras and digital music players. However, batteries or lithium batteries currently on the market deserve improvements in terms of price, reliability, energy return, environmental impact and service life. A battery is a transducer that converts chemical energy into electrical energy. This conversion of chemical energy into electrical energy will be called direct operation of the battery or battery. In the case of a rechargeable battery or battery, it is also possible to perform the reverse operation, that is to say to convert the electrical energy into chemical energy, which will itself be reused. This operation will be called reverse operation. A battery or battery comprises an anode, a cathode and an electrolyte. The anode constitutes the negative pole, while the cathode constitutes the positive pole of the battery or battery. The electrolyte itself allows the transport of lithium ions and electrons.

Generally, the anode consists of a low potential carbon material serving as a host to Lithium Lit ions. This technology, which has made it possible to overcome the use of lithium metal anodes posing real security problems, has allowed the commercial development of lithium batteries.

For the purposes of the present invention, the term "active cathode material" means the material which undergoes the electrochemical transformation (or oxidation-reduction reaction) in the cathode. The active cathode material can be used in admixture with additives. These additives are preferably plasticizers, binders, materials to improve the conductivity of the cathode (such as carbon black). For the purposes of the present invention, however, the "active cathode material" does not include these additives. Currently, the most used active cathode materials are oxides based on cobalt, manganese and iron, for which materials of LixCo02 and LiFePO4 type are preferred because of the values of their redox potential of 3.5V for Fe 3 '/ Fe2 'and Co3' / Co2 'with respect to the potential of the Li' / Li couple. However, these materials, including cobalt oxides, do not meet ecological requirements because they are pollutants (heavy metals) and difficult to recycle. In addition, systems using cobalt oxides have overheating problems in the event of cathode and / or electrolyte overload, while LiFePO4 based systems suffer from relatively low inherent conductivity. Vanadium oxides, which are much more "ecological", are considered as promising active cathode materials because of the redox potentials V5 '/ V4' and V4 'N3' close to 2.7 and 2.0V respectively relative to the potential of the Li 'pair. / Li. In particular, the material V205 involves two potentials: V5 + / V4 + and V4 + / V3 + during the intercalation of lithium ions by V205. The operation of such a battery is therefore complex, involving the appearance of two different redox potentials that are likely to affect the reliability of the battery. In addition, the intercalation of lithium ions in V205 introduces structural phase transitions that are likely to weaken the electrode material. Similarly, the LiV308 material involves the two redox couples V5 '/ V4' and v4 + N3 +.

The advantages and disadvantages of active cathode materials most commonly used in lithium batteries or batteries are presented more generally in the Witthingham review published in Chem. Rev. 2004, 104, 4271-4301, in the article by Nazar et al. published in Chem. Mater. 2010, 22, 691-714 and in the article by Armand and Tarascon published in Nature 2008, 451, 652-657.

There is therefore a need for new cathode active materials that would be both environmentally friendly, economical, reliable, and with a redox potential adapted for efficient energy storage and retrieval in rechargeable lithium batteries. Surprisingly, the inventors have discovered that the material Li2_xV03_y, with x representing a number such that 0 <x <1 and y represents a number such that 0 <y <0.1, is selective in terms of the potentials involved during the phenomenon of intercalation-deintercalation: it only concerns the redox couple V5W4 + corresponding to the intercalation of a lithium ion by vanadium. It can intercalate / intercalate one lithium per vanadium with excellent reversibility at the average potential of 2.5 V for the Li + / Li pair. As indicated above, such a material has a redox potential adapted for efficient energy storage and restitution and is ecological. An object of the present invention is therefore an active cathode material comprising a composition of formula Li2_xV03_y with x a number such that 0 <x <1 and y represents a number such that 0 <y <0.1. Another object of the present invention is to provide a method of manufacturing an active cathode material comprising a composition of the formula Li 2, VO 3 y with x a number such that 0 <x <1 and y represents a number such that 0 <y <0.1. Another object of the present invention relates to the use of such cathode materials for the manufacture of rechargeable lithium batteries.

Another object of the present invention relates to rechargeable lithium batteries or cells comprising the active cathode material according to the invention. The present invention thus relates to an active cathode material comprising a composition of the formula Li 2, VO 3 - where x represents a number such that 0 <x <1 and y represents a number such that 0 <y <0.1. The active cathode material Li2_xV03_y where x represents a number such that 0 <x <1 and y represents a number such that 0 <y <0.1 comprises vanadium at V4 + degree. The number y such that 0 <y <0.1 makes it possible to define any defects that inevitably occur in the structure of the material according to the invention. However, if y is greater than 0.1, then the defects of the spatial structure would be too great and would result in the collapse of the material structure. Preferably, y represents a number such that 0 <y <0.01, more preferably, y represents a number such that 0 <y <0.001, even more preferentially, y is equal to 0. Advantageously, the active cathode material Li2, V03_y where x represents a number such that 0 <x <1 and y represents a number such that 0 <y <0.1 has a centered cubic mesh structure. This structure is disordered, that is to say that the location of the ions Le and V4 + in the centered cubic mesh is random. Furthermore, the size of the mesh is such that it does not allow to insert more than 2 lithium ions per mesh. When using the active cathode material according to the invention in a lithium battery or cell, the lithium can be deintercaled in a completely reversible manner in the material which behaves like a solid solution Li2_xV03_y where x represents a number such that 0 <x <1 and y represents a number such that 0 <y <0.1. Advantageously, the centered cubic mesh type structure of the active cathode material according to the invention allows a high reactivity and consequently excellent operating conditions, avoiding the stresses that are often harmful during the cycling phenomena to which the electrode materials are subjected. , in particular for cathodes.

Advantageously, the intercalation is completely reversible, the limit material LiVO3 (x = 1) formed by chemical deintercalation in the battery can again intercalate lithium by electrochemical treatment in the battery reversibly leading to active cathode material Li2V03. It should be noted that the material LiVO3 is indeed a theoretical limit compound, all the measurements made on the material "discharged", that is to say when the chemical deintercalation in the battery is finished, always giving values of x such that x <1. Indeed, the structure of LiVO3 (x = 1) is an ordered and ribbon structure, therefore very different from that of the active cathode material according to the invention. When the LiVO3 material is brought into contact with a lithium source capable of undergoing a redox reaction, the chemical transformation leading to the material according to the invention is accompanied by an irreversible structure change. Thus, irrespective of the value of x lying between x = 0 and x <1, the cathode material according to the invention retains a centered cubic mesh structure deficient in lithium. The cathode material according to the invention is therefore an excellent electronic and ionic conductor. In addition, the cathode material according to the invention is chemically and thermally stable. On the other hand, in the case of a material of formula LixV03_y where x represents a number such that x> 2 and y represents a number such that 0 <y <0.1, the structure changes completely and the formula of the material is more exactly represented by a mixture of Li20 and VO2 and V. For example, for x = 6 the formula would be (Li20) 3 + V. The spatial arrangement is not at all comparable to a network of cubic meshes centered. This results in instability of the material, whose structure is poorly defined and likely to change during use. x therefore advantageously represents a number such that 0 <x <0.5, more advantageously x is equal to 0. In one embodiment, the active cathode material according to the invention further comprises another active cathode material.

In another embodiment, the active cathode material according to the invention consists only of a composition of formula Li 2-xVO 3-y where x represents a number such that 0 <x <1 and y represents a number such that 0 <y <0.1. The present invention also relates to a method of manufacturing active cathode material according to the invention. The synthesis of the cathode material according to the invention is extremely simple and very advantageous in economic and practical terms. The method of manufacture comprises the following steps: (a) Formation of the oxide LiV03_y with y being a number such that 0 <y <0.1; (b) contacting the oxide LiV03_y with y as defined above obtained in step (a) with a lithium source capable of undergoing a redox reaction; and (c) recovering and then drying the solid active cathode material obtained. The processes for synthesizing LiV03_y with y representing a number such that 15 0 <y <0.1 are known to those skilled in the art. By "lithium source capable of undergoing a redox reaction" is meant a source comprising lithium in Li 'or Li ° form, for example lithium metal, capable of reducing vanadium and of providing an Li' ion. In a preferred embodiment, however, a method is used involving heating a mixture of V205 and Li2CO3 lithium carbonate in an air atmosphere at a temperature between 400 ° C and 800 ° C, preferably between 500 ° C. C and 600 ° C, even more preferably 550 ° C, for a period between 1h and 24h, more preferably equal to 12h. The lithium source capable of undergoing a redox reaction comprises at least one organic chemical reagent or at least one inorganic chemical reagent. In one embodiment, the lithium source capable of undergoing a redox reaction comprises at least one organic chemical reagent.

A non-limiting example of an organic chemical reagent is n-butyllithium dissolved in a solvent compatible with n-butyllithium. Advantageously, the solvent compatible with the n-butyllithium used in step (b) is chosen from the group of hydrocarbon solvents and ethereal solvents, advantageously from the group of hexane, toluene, cyclohexane and ether. diethyl. Advantageously, the reaction with butyllithium takes place under an inert atmosphere for a period of between 6h and 100h, advantageously between 12h and 96h, even more advantageously between 48h and 80h, even more advantageously it is 72h. The product obtained is filtered, and has the formula Li2_xV03_y where x represents a number such that 0 <x <1 and y represents a number such that 0 <y <0.1, as a function of the number of equivalents of n-butyllithium used during step (b). In one embodiment, the lithium source capable of undergoing a redox reaction comprises at least one inorganic chemical reagent. Lithium sources capable of undergoing a redox reaction comprising at least one inorganic chemical reagent as well as the implementation of a redox type reaction making it possible to pass from LiV03_y with y representing a number such that 0 <y <0.1 to the cathode material active according to the invention are well known to those skilled in the art. For example, such a redox reaction can be done in the context of a lithium battery in reverse operation, that is to say in a configuration that would correspond to recharging the battery. As indicated above, there is an irreversible structure change in the reaction allowing the transformation of LiV03_y with y representing a number such that 0 <y <0.1 in Li2, V03_y where x is a number such that 0 <x < let y represents a number such that 0 <y <0.1. Since this structural transformation is important, it is preferable to use an active starting cathode material according to the invention and not the known material LiV03_y with y representing a number such that 0 <y <0.1. Indeed, a battery comprising a LiV03_y starting active cathode material with y representing a number such that 0 <y <0.1 would have a compromised mechanical, thermal and chemical stability. Advantageously, step b) of the method of manufacturing the active cathode material according to the invention does not take place directly in the stack.

In one embodiment of the invention, LiV03_y with y representing a number such that 0 <y <0.1 is deposited as a thin film on a surface. The material thus obtained is then dipped in a solution containing a chemical or electrochemical lithium source capable of undergoing a redox reaction. A thin film of active cathode material according to the invention is then obtained on the surface. The present invention also relates to the use of the active cathode material according to the invention for the manufacture of lithium batteries or batteries. Preferably, these batteries are rechargeable. Advantageously, the active cathode material according to the invention is used in admixture with additives, advantageously binders, plasticizers or materials designed to improve the conductivity of the electrode. In one embodiment of the invention, the electrolyte of the lithium battery or cell comprises LiC104. In one embodiment of the invention, the electrolyte of the battery or lithium battery is contained in propylene carbonate, ethylene carbonate, dimethyl carbonate, or mixtures thereof. In one embodiment of the invention, the anode of the battery or lithium battery comprises a carbon material, preferably graphite. In one embodiment of the invention, the cathode of the battery or lithium battery according to the invention comprises an active cathode material according to the invention alone or in combination with other active cathode materials or additives, a LiC1O4 electrolyte. and a lithium metal anode Li. In another embodiment, the anode is comprised of a carbon material, preferably graphite.

In addition, the cathode material according to the invention has all the essential characteristics for developing thin-film electrodes for micro-batteries. For the purposes of the present invention, the term "micro-battery" is intended to mean a battery or battery having a characteristic size of a few micrometers. In this embodiment of the invention, the cathode active material is deposited in the form of a thin film. Preferably, the thin film is deposited by a sol-gel or electrochemical method. Preferably, the sol-gel method comprises a spraying step. Preferably, the electrochemical method comprises a step of electrodeposition or electrophoresis. The present invention also relates to a lithium battery or battery comprising, as cathode, the cathode active material according to the invention. Preferably, these batteries are rechargeable. Advantageously, the cathode of the battery according to the invention further comprises additives, advantageously binders, plasticizers or materials to improve the conductivity of the electrode. In one embodiment of the invention, the electrolyte of the lithium battery or cell comprises LiC104. In one embodiment of the invention, the electrolyte of the battery or lithium battery is contained in propylene carbonate, ethylene carbonate, dimethyl carbonate, or mixtures thereof. In one embodiment of the invention, the anode of the battery or lithium battery comprises a carbon material, preferably graphite. In one embodiment of the invention, the lithium battery or battery comprises the active cathode material according to the invention as a cathode, a LiC104 electrolyte and a lithium metal anode Li. These cells deliver a specific capacity of 253 mAh / g and the specific energy is 632Wh / kg. In one embodiment of the invention, the battery or battery is a micro-battery.

Fig 1: Structure of LiVO3 along the b (left) axis and Structure of Li2V03 (right). The LiVO3 material obtained by the process according to the invention makes it possible to obtain a perfectly crystalline phase. The structure of LiVO3 could be described as layers of Li06 octahedra connected by chains of VO4 tetrahedra parallel to the c axis. The figure clearly shows the difference with the "centered cubic mesh" type structure of Li2V03, and illustrates the change in structure of the LiVO3 material when it is placed in the presence of a Li + source capable of undergoing a redox reaction to give the Li2V03 material. Fig 2: Potential curve (in Volts) of Li2, V03 at a rate of C / 10 as a function of x. This figure shows the reversible nature of the process. The material reacts as a solid solution of cubic mesh type structure centered defective in Lit. Fig 3: Capacity (mA.h / g) according to the number of cycles for a rate of C / 10. This figure demonstrates that the performances of the cathode active material according to the invention are stable in cycling. FIG. 4: Comparison of the specific energy performances (kWh / kg, histogram) and average potential Li + / Li (V, horizontal lines) of the cathode materials of the prior art with the Li2V03 phase. The following examples are intended to further illustrate the present invention, but are in no way limiting. Example 1: Manufacture of cathodic material Li2V03 a. Manufacturing Process In a first step the LiVO3 oxide is prepared by heating a mixture of V205 and Li2CO3 lithium carbonate in air at 550 ° C for 12 hours (step a).

LiVO 3 is then placed in the presence of a solution of n-butyllithium (2.5M) in hexane for 72 h under an inert atmosphere (step b). The product obtained is filtered and dried (stage c). It is ready for use. It has the formula Li2, V03 where x represents a number such that 0 <x <1, as a function of the number of equivalents of n-butyllithium used in step (b). b. Characterization of the cathodic material Li2VO3 The chemical analyzes carried out by atomic absorption make it possible to determine the exact content of lithium and consequently the formula of the material is indeed Li2VO3, with the measurement error.

Fig. 2 shows the centered cubic mesh structure of Li2VO3. c. Use of Li2VO3 cathode material in a lithium rechargeable battery Li2VO3 can deintercale lithium reversibly, with perfect reversibility at an average potential of 2.5 V vs U / Li, resulting in a specific capacity of 253 mAh / g and the specific energy of 632 Wh / kg. The operating characteristics of the Li2VO3 active cathode material are shown in FIG. 3. The electrochemical study of Li2VO3 shows its capacity to intercalate a lithium per formula. The charge / discharge profiles were performed by a C / 10 galvanostatic cycling in the potential window of 1.0-3.0 V versus U / Li (Fig. 3). The first discharge consists of the insertion of a lithium, leading to the Li2VO3 phase. After the first cycle, a reversible capacity of 0.9 Li / form unit (fu) (250 mAh / g) is obtained at an average potential of 2.5V. The reversible process of insertion is a solid solution type process. Comparative Example LiV03 FIG. 3 illustrates the irreversible transformation which takes place during the first cycle of the battery. Indeed, during the first cycle (1), which corresponds to the insertion of a lithium by LiVO3 formula, a plateau corresponding to a dual mechanism is observed, leading to the formation of Li2VO3 material with a cubic mesh type structure. centered. After the first cycle, the process becomes reversible (2 and 3) and the material reacts as a solid solution of cubic lattice-like structure deficient in Li '.

Other Comparative Examples FIG. 5 makes it possible to compare the specific energy performances (kWh / kg) and average Li / Li potential of the cathode materials of the prior art with the Li2VO3 phase.

It appears very clearly that the material according to the invention, illustrated by Li2VO3 is more efficient in terms of specific energy (632Wh / kg) compared to all the materials presented. However, cobalt oxide LiCoO 2 (Formula 1) is not only made of a polluting heavy metal (cobalt) but is very expensive. The manganese oxide Li 2 MnO 4 (formula 2) suffers partial dissolution during its use in a lithium battery, which limits its application. Similarly, the material of formula 4 is also very polluting and expensive. The LiFePO4 material of formula 3 for its part has a specific energy very much lower than that of the material according to the invention (formula 5).

Claims (13)

REVENDICATIONS1. Active cathode material comprising a composition of the formula Li 2, VO 3 - where x represents a number such that 0 <x <1 and y represents a number such that 0 <y <0.1. 2. Cathode material according to claim 1, characterized in that y is equal to O. 3. Cathode material according to claim 1 or 2, characterized in that x is equal to O. 4. A method of manufacturing a material according to any one of claims 1 to 3, comprising the following steps: (a) Formation of LiV03_y oxide; (b) contacting the oxide LiV03_y with y as defined above obtained in step (a) with a lithium source capable of undergoing a redox reaction; and (c) recovering and then drying the solid active cathode material obtained. 5. Method according to claim 4, characterized in that the lithium source capable of undergoing a redox reaction comprises at least one organic chemical reagent. 6. Use of a cathode material according to any one of claims 1 to 3 for the manufacture of a lithium battery or battery. 7. Use according to claim 6, characterized in that the battery or lithium battery is rechargeable. 8. Battery or lithium battery comprising as cathode active cathode material according to any one of claims 1 to 3. 9. Lithium battery or battery according to claim 8, characterized in that it is rechargeable. 25 10. Battery or lithium battery according to any one of claims 8 or 9, characterized in that the electrolyte of the battery or lithium battery comprises LiC104. 11. Lithium battery according to claim 8, characterized in that the electrolyte of the lithium battery or cell is contained in propylene carbonate, ethylene carbonate or dimethyl carbonate, or mixtures. 12. Battery or lithium battery according to any one of claims 8 to 11, characterized in that the anode of the battery or battery comprises a carbon material, preferably graphite. 13. Battery or battery according to any one of claims 8 to 12, characterized in that the cathode further comprises additives, preferably binders, plasticizers or materials to improve the conductivity of the electrode.