ORGANIC ELECTROLYTE CELL

Abstract: An organic electrolyte cell is disclosed which comprises an anode (2) made of Li or Li alloy, an organic electrolyte and cathode active material (5) made of Li and metal complex oxide represented by LiMO₂ wherein M stands for at least one of Co, Ni, Fe, Cr, and V. The cell has a discharge voltage of 1.2 to 1.3 volts which is compatible with mercury cell.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an organic electrolyte cell using lithium or lithium alloy as the anode, liquid organic electrolyte and cathode material. Prior Art Recently, in association with the miniaturization of various eletronic equipment such as timepiece, cameras or electronic calculators, silver oxide or mercury cells that are small in size and thickness and having high energy density among the aqueous solution cells are being used. However, with our increased interest in environmental pollution problems, since not only mercury cells but also the silver oxide cells make use of zinc amalgam as the cathode, it is feared that disposal of used mercury and silver oxide cells may cause additional environmental pollution. Under these circumstances, possible debut of the pollution free cells interchangeable with mercury of silver oxide cells is strongly desired. On the other hand, lithium cells using lithium or alloy as the cathode and an organic liquid electrolyte as the liquid electrolyte is superior in storage properties, can be reduced in size and thickness because of its high energy density, while it is pollution-free in that it does not make use of mercury, so that it is tentatively used in a variety of electronic devices.EP-A-0 017 400 discloses an electrochemical cell comprising a liquid or solid electrolyte arranged between solid-solution electrodes. At least one of the solid-solution electrodes is constituted by a mixed metal oxide Li x M y O z , in which M may comprise Ni and Co. The cell reactions occur by liberating Li from Li x M y O z during charging which results in a discharge voltage of 4V. From US-A-4 567 031 a process for preparing a mixed metal oxide is known which is usable as cathode or intercalation electrode in high energy density primary and secondary batteries, having the formula Li x M y O z where M is at least one metal selected from the group consisting of i.a. cobalt and nickel. For example, lithium cells using MnO₂, CF X and AgCrO₄ as the anode active material are finding practical application. However, because of its higher cell voltage of 3 V, the lithium cell is not fully satisfactory in its interchangeability with the conventional mercury of silver oxide cells. It has been tried to evolve lithium cells interchangeable with these silver oxide or mercury cells and there has been proposed a lithium cell using FeS, FeS₂ or CuO as the cathode active material in combination with the lithium anode. This lithium cell has a cell voltage of 1.5 to 1.6 V and thus approximately equal to that of the silver oxide cell so that the interchangeability with the silver oxide cell is assured. However, the mercury cell has a lower cell voltage of 1.3 V, such that there lacks up to now a lithium cell fully interchangeable with the mercury cell. OBJECT AND SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an organic electrolyte cell which is free from mercury It is another object of the present invention to provide an organic electrolyte cell having voltage which is compatible with mercury cell. It is further object of the present invention to provide an organic electrolyte cell having increased cell capacity. According to the present invention there is provided an organic electrolyte cell which comprises an anode made of lithium or lithium alloy, an organic electrolyte, and cathode containing cathod active material made of Li and metal complex oxide represented by LiCo₁₋ x Ni x O₂ BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an enlarged sectional view showing an example of the structure of the organic electrolyte cell; Fig. 2A and 2B are spectral diagrams showing the X-ray diffraction patterns when the value of x in LiNi x Co₁₋ x O₂ is changed stepwise from 0 to 1, wherein Fig. 2A that for LiNi₀ . ₁Co₀ . ₉O₂; Fig. 2B that for LiNi₀ . ₂Co₀ . ₈O₂; Fig. 3 is a diagram showing the relation between the value of x and the discharge time per unit weight for a cell having LiNi x Co ( ₁₋ x) O₂ as the anode material; and Fig. 4 is a diagram showing the discharge curve of the cell having LiNi₀ . ₁Co₀ . ₉O₂ as the anode material in comparison with the cell having LiCoO₂ as the anode material and the cell having LiNiO₂ as the anode material. DESCRIPTION OF THE PREFERRED EMBODIMENTS Since the cell voltage is determined by its cathode and anode material, the present inventors have investigated into various cathode materials in combination with the anode lithium. As the result, we have found a material exhibiting an electrical voltage approximately equal to the working voltage of the mercury cell (1.2 to 1.3V). Thus the organic electrolyte cell of the present invention is characterized in that it is constituted by an anode of lithium or lithium alloy, a cathode formed of a complex metal oxide represented by LiCo₁₋ x Ni x O₂, and an organic electrolyte. The aforementioned complex metal oxide may be produced easily by mixing and heat treating carbonates of Li and carbonates of Ni and Co. As the anode active material, an alloy of Li with one or more of Al, Pb, Sn, Bi and Cd, such as LiAl alloy, may be used in addition to lithium. As the electrolyte solution, a non-aqueous organic electrolyte of a lithium salt dissolved in an organic solvent may be used. The organic solvent includes esters, ethers, 3-substituted-2-oxazolidine, or a mixed solvent consisting of two or more of these solvents. The esters may include alkylene carbonates (ethylene carbonates, propylene carbonates or γ-butyrolactones). The ethers may include cyclic ethers, such as 5-membered ethers tetrahydrofuran; substituted (alkyl, alkoxy) tetrahydrofuran, such as 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2-ethyltetrahydrofuran, 2,2′-dimethyltetrahydrofuran, 2-methoxytetrahydrofuran, or 2,5-dimethoxytetrahydrofuran; or dioxolane, 6-membered ethers 1,4-dioxane, pyran, dihydropyran, or tetrahydrofuran, or dimethoxyethane. The 3-substituted oxazolidinones include 3-alkyl-2-oxazolidinones (such as 3-methyl-2 oxazolidinone, or 3-ethyl-2-oxazolidinone); 3-cycloalkyl-2-oxazolidinones (such as 3-cyclohexyl-2-oxazolidinone), 3-aralkyl-2-oxazolidinones (such as 3-benzyl-2-oxazolidinone), or 3-aryl-2-oxazolidinone (3-phenyl-2-oxazolidinone). Above all, propylene carbonates or 5-membered ethers (above all, tetrahydrofuran, 2-methyltetrahydrofuran, 2-ethyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, or 2-methoxytetrahydrofuran), or 3-methyl-2-oxazolidinone. As the electrolyte, lithium perchlorate, boron lithium fluoride, phosphorus lithium fluoride, lithium aluminate chloride, or trifluoromethane lithium sulfonate. Of these lithium perchlorate or boron lithium fluoride is preferred. The cathode material that has brought the present invention to completion is a complex oxide of lithium and the transition metal (M) represented by the chemical formula LiMO₂ in which M represents Co₁₋ x Ni x . The cell reaction is considered to proceed by the reaction schema shown by the formula (1), with the operating voltage being 1.2 to 1.3V. That is, in the organic electrolyte cell of the present invention, the complex metal compound, the cathode material, is reduced to an oxidized state of the lower order, with the reaction proceeds from M³⁺ to M⁰. Taking an example of LiCoO₂, the reaction proceeds from Co³⁺ to Co⁰, as indicated by the formula LiCoO₂ + 3Li → 2Li₂O + Co⁰ The sample applies to the case of LiNiO₂, wherein LiNi O2 is discharged such that LiNiO₂ + 3Li → 2Li₂0 + Ni⁰ In this case, the cell voltage corresponds to the potential difference between LiCoO₂ and Li or between LiNiO₂ and Li is set to 1.2 to 1.3 V. Also, in the organic electrolyte cell of the present invention, the cell reaction between the cathode material LiCo₁₋ x Ni x O₂ and the anode material Li proceeds in the three-electron reaction so that the theoretical capacity is as large as 821 mAH/g and 823 mAH/g, respectively, so that a cell of a large capacity is obtained. Moreover, by charging, the oxidized state of a higher order, or the pre-charging state, may be obtained, as shown by the formula so that the cell may also be used as the secondary cell. Wherein using the cell as the secondary cell in this manner, the charging voltage is preferably kept so as to be not higher than 2.5 V. If the charging voltage becomes excessive, the organic electrolyte tends to be decomposed. The present invention will be explained with reference to certain specific examples. It is to be noted, however, that the present invention is not to be limited to these Examples. Synthesis of LiCoO₂ and LiNiO₂ as reference materials 36.9 g of marketed lithium carbonate and 118.9 g of powdered cobalt carbonate were mixed thoroughly and calcined at 900 C for 5 hours in air. On examination by an X-ray diffraction, the calcined product showed the diffraction pattern of LiCoO₂. Similarly, powedred lithium carbonate and powdered nickel carbonate were mixed together thoroughly at a ration that will give an atomic ration of lithium to nickel of 1:1 and the resulting mixture was calcined in air at 900 C for 5 hours. On examination by X-ray diffraction, the calcined product showed the diffraction pattern of LiNiO₂. Synthesis Example of Complex Oxides The commercially available lithium carbonate powders and cobalt carbonate powders were mixed together to give a lithium atom to cobalt atom ratio of 1:1 and the mixture was calcined in air at 900°C for 5 hours to a lithium-cobalt complex oxide (LiCoO₂), Then, to replace the cobalt atoms of the lithium cobalt complex oxide by nickel atoms, lithium carbonate (LiCO₃), cobalt carbonate (CoCO₃) and nickel carbonate (NiCO₃) were mixed to conform to a composition of Li-Ni x Co₁₋ x O₂ and calcined. That is, for various values of x , mixing and calcining were so performed that the lithium atoms, nickel atoms and cobalt atoms obey the ratio of (1:x:1-x). The calcining conditions were 900°C for 5 hours in air, as in the case of the lithium cobalt complex oxides. Figs. 2A and 2B show the X-ray diffraction patterns for These complex oxides. Thus, Fig. 2A shows LiNi₀ . ₁Co₀ . ₉O₂; Fig. 2B shows LiNi₀₋₂Co 0. ₈O₂; Example 2 To 7.0 wt.parts of the powders of complex oxide LiNi x Co₁₋ x O₂ (x=0-1) prepared in the preceding synthetic example for the complex oxide and reference materials LiCoO₂ and LiNiO₂ or x=0 and x=1 were mixed with 27 wt. part of the graphite and 3 wt.parts of polytetrafluoroethylene powders as the binder, and the resulting powder mixture was compacted and formed to a cathode pellet 10.3 mm in diameter and 0.5 mm in thickness. Then, as shown in Fig.1, a lithium foil (2) 12.3 mm in diameter and 1.6 mm in thickness was punched and pressed onto an anode cup (1). On this was placed a separator (3) containing the electrolyte liquid, a plastic gasket (4) was fitted, the cathode pellet (5) was placed on the separator (3), assemble an organic electrolyte cell. As the electrolyte liquid, lithiumperchlorate dissolved in propylene carbonate at a rate of 1 mol/liter was used. These cells were discharged through a resistor of 6.5 kiloohms and the discharge time until the terminal voltage of 1.2 V was measured to find the discharge time of the cathode material LiNi x Co₁₋ x O₂ per unit weight (1 mg) The results are shown in Fig. 3. It is seen from Fig. 3 that the discharge capacity of the cell using LiNi x Co₁₋ x O₂ as the cathode material is changed with the value of x and that the discharge capacity is increased as compared to LiCoO₂ when part of cobalt is replaced by nickel. However, the capacity is decreased with the increase in the nickel contents for x > 0.27. Thus it was proved in the present Example that the complex oxide consisting of lithium, cobalt and nickel LiNi x Co₁₋ x O₂ wherein x is greater than 0 and not larger than 0.27 in atomic ration is excellent as the cell active material and, above all, the oxide in which part of the cobalt atoms are replaced by nickel atoms by setting the value of x according to the invention so that 0 < x ≦ 0.27 proves to be an excellent cell active material in an organic electrolyte cell having the reaction of the formula wherein M represents Ni x Co₁₋ x , as the basic cell reaction. Fig. 4 shows the characteristics of the discharge curve of the Li/LiNi₀ . ₁Co₀ . ₉O₂ cell as compared to those of Li/LiCoO₂ reference cell and Li/LiNiO₂ reference cell, wherein the maximum value is indicated by the discharge capacity. The ascendancy of using LiNi x Co₁ -x O₂ as the cathode material may also be proved from Fig.4. The cell having LiCoO₂ as the cathode material is satisfactory in regard to the discharge voltage, however, it is not fully satisfactory in regard to the discharge capacity. On the other hand, the cell having LiNiO₂ as the cathode material has a flat discharge curve and exhibits desirable properties in the cell life, however, it has a slightly low discharge voltage such that the cell capacity can hardly be procured for a terminal voltage of 1.2 V. On the other hand, the cell having LiNi 0.1 Co 0.9 O₂ as the anode material according to the invention showed satisfactory properties in both the discharge voltage and discharge capacity. The mercury cell, having a desirably large capacity, poses a pollution probleme because it makes use of a large amount of mercury and the disposal of the used cells causes difficulties. However, these cells are still being used because of the absence of proper substitutes. The present invention has realized a pollution-free lithium cell that is fully interchangeable with the mercury cell as to the operating voltage thereof. The present invention provides a novel cell system wherein a cathode lithium is combined with the anode lithium-nickel-cobalt complex oxide to realize a cell having an operating voltage of 1.2 to 1.3 V and thus a totally equivalent voltage to that of the mercury cell. Rather, the cell capacity of the cell is larger than that of the mercury cell. By using LiCoO₂ as the basic active material with part of the cobalt atoms thereof replaced by nickel atoms with an atomic ratio for Ni greater than 0 and not larger than 0.27, the discharge capacity of the cell is increased significantly.

Claims: An organic electrolyte cell comprising an anode made of Li or Li alloy, an organic electrolyte and a cathode containing a cathode active material made of Li and a metal complex oxide represented by LiCo ₁ -x Ni x O₂ wherein x is greater than 0 and not larger than 0.27 in atomic ratio, whereby the cell voltage corresponds to the potential difference between LiCo ₁ -x Ni x O₂ and Li.

Inventors: HASHIMOTO, TOSHIO C/O SONY ENERGYTEC INC., NAGAURA, TORU C/O SONY ENERGYTEC INC.
Applicants: SONY CORPORATION
Application year: 1987
Main classification: H01M4
IPC codes: H01M10, H01M4