JPH0322025B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a non-aqueous chemical battery, particularly a non-aqueous chemical battery containing an electrolyte solvent that easily oxidizes and generates gas.
More particularly, the present invention relates to the above-mentioned battery containing a manganese dioxide cathode.

Recent developments in high energy density chemical battery systems (those involving active metals such as lithium and non-aqueous electrolyte carriers) include substantially beta manganese dioxide (ca.
(approximately 95% beta type) may be used. For such cathode materials to be used successfully in non-aqueous batteries, the manganese dioxide must first be subjected to several rounds of severe (above 200°C) heat treatment to convert the electrolytic gamma-type manganese dioxide into substantially beta-type manganese dioxide. Change to manganese. After forming the cathode, e.g. Eliminate all residual water. As described in U.S. Pat. No. 4,133,856, the first heat treatment is carried out at a temperature of 350-430C and the second heat treatment of the shaped cathode is carried out at a temperature of 200-350C. If a temperature of 200°C or less is used in the second heat treatment,
It is stated that this will result in a significant reduction in battery capacity.

Our patent application No. 118241 (August 1979)
Corresponding to U.S. Patent Application No. 70198, dated 27th),
The probable cause of the decrease in battery capacity as described above is
It is stated that this is caused by the loss of battery stability caused by the interaction between the propylene carbonate (PC) electrolyte solvent, lithium perchlorate electrolyte salt, and residual water within the battery. This interaction results in the decomposition of propylene carbonate and the evolution of a harmful gas (probably _CO2 ). Such harmful gas generation by substituting another specific electrolyte solvent and/or electrolyte salt as described in the above specification is a requirement in U.S. Pat. No. 4,133,856. It has been discovered that this can be minimized without the need for severe heat treatment. but,
Electrolyte solvents such as propylene carbonate (PC) and electrolyte salts such as lithium perchlorate exhibit high conductivity despite their cell instability shortcomings without severe heat treatment of the formed cathode. Therefore, it is preferable as a battery component.

One object of the present invention is to provide a method for manufacturing a non-aqueous battery that can utilize a decomposable and gas-generating electrolyte solvent without requiring severe heat treatment of a formed cathode.

Another object of the present invention is to provide a non-aqueous chemical cell that includes an inorganic additive that substantially suppresses electrolyte solvent decomposition and associated gas generation.

Yet another object of the present invention is to provide a non-aqueous battery cathode that does not function as a reaction site where the solvent-decomposing reaction described above occurs.

Other objects, features, and advantages of the present invention will become more apparent from the following description.

The present invention relates generally to methods for making stabilized non-aqueous chemical cells, and more particularly to stabilized non-aqueous chemical cells containing electrolyte solvents that are susceptible to interaction with other cell components and associated gas generation. Concerning the manufacturing method. As described in our above patent application, the decomposition of electrolyte solvents is due to the interaction between the solvent and dissolved electrolyte salts, which are converted into strong oxidizing agents by the water remaining in the cell. This is considered to be a result of this. Furthermore, it has now become fully conceivable that another element in the decomposition reaction process is a reaction generating site provided by the cathode material for such decomposition. It has now been discovered that by partially deactivating substantially all of the active surface reaction sites on the cathode prior to the initial discharge of the cell, electrolyte solvent decomposition and gas evolution are significantly reduced. . Preferably, such partial deactivation is performed by uniformly distributing an inorganic cathode surface deactivating additive within the cathode. Here, partial deactivation refers to deactivation of the active cathode surface that substantially controls electrolyte solvent decomposition and associated gas generation, but where the cathode undergoes a substantial reduction in electrochemical properties. This means minimizing the depth to a point where there is no depth. Therefore, it is more preferred that such inorganic additives be present in the cathode in an additive amount of up to about 5% by weight.

Examples of inorganic additives that have been found to partially deactivate the active surface of the cathode and thus reduce solvent decomposition and gassing include nitrates such as lithium nitrate and calcium nitrate, and other alkali and Included are metal salts such as alkaline earth metal nitrates and nitrites. The inorganic additives used as additives in the cells of the invention have the property of reacting with the active surface functional groups on the cathode surface and converting those functional groups to a less active state. Such a reaction may be (a) a chemically induced partial cell discharge reaction prior to the actual cell discharge, or (b) a spontaneous or thermal reaction between the active inorganic additive and the active cathode surface. This is a reaction induced by Such reactions partially deactivate substantially all of the cathode surface, which serves as a reaction site for decomposition of the electrolyte solvent.

The method for making cathodes with inorganic additives involves thoroughly mixing the powdered active cathode material and the inorganic additive solution, evaporating the solvent, and then subjecting the mixture to a reaction process over substantially the entire surface of the active cathode. and a treatment for partial deactivation (for example, by heating, if necessary). The use of solvated inorganic additives in such mixtures allows intimate contact with virtually all cathode surfaces. The surface-passivated cathode material is then formed into a cathode for insertion and placement into a cell using standard methods, without the additional precision required for previously formed cathodes. No additional heat treatment is required. Alternatively, inorganic additives may be present in the completed battery to complete the battery with an active metal anode such as lithium (a metal above hydrogen in the EMF ranking series), an active cathode and a non-aqueous electrolyte solution. The active surface of the cathode may be partially deactivated using the inorganic additive. Such inorganic additives are selected to cause incomplete discharge of the cathode and, since the discharge reaction is initiated at the surface of the cathode, thereby partially deactivating the surface of the cathode. Inorganic additives are particularly effective when brought into close proximity to the cathode, for example by mixing. However, inorganic additives may also be present in the battery electrolyte.

The present invention is particularly useful when used with manganese dioxide cathodes. In such a non-aqueous chemical battery, gamma and
This is because it is necessary to convert manganese dioxide into beta-manganese dioxide through ignition treatment at 375 to 400°C. Therefore, by first mixing gamma manganese dioxide with an inorganic additive such as lithium nitrate or calcium nitrate, beta-manganese dioxide can be prepared.
Conversion to manganese dioxide will occur simultaneously with a thermally initiated reaction of the lithium or calcium nitrate with the cathode surface and deactivation of the active beta manganese dioxide surface. A second heating step after cathode formation as required in U.S. Pat. However, even when using an electrolyte medium that generates gas, it is omitted. Therefore, electrolyte solvents that decompose to generate gaseous decomposition products, such as propylene carbonate (PC) and dimethoxyethane (DME), which have been used in non-aqueous batteries containing beta-manganese dioxide, decompose. Aqueous electrolyte solvents may be used with electrolyte salts that form strong oxidizing agents in the presence of water, such as perchlorate, hexafluoroarsenate and trifluoroacetate.

Since it is the residual water in the cell (especially the cathode) that initiates the decomposition of the electrolyte solvent and the formation of gaseous reaction products, the present invention relates to cells having metal oxide cathodes with strong water retention properties. Particularly useful. Examples of metal oxides that easily retain water include the aforementioned manganese dioxide, TiO ₂ , SnO,
MoO ₃ , V ₂ O ₃ , CrO ₃ , PbO, Fe ₂ O ₃ and generally transition metal oxides. However, it will be appreciated that the present invention is effective whenever residual water is present in the cell that causes a reaction that decomposes the electrolyte solvent and generates gas.

Generally, batteries are constructed using corrosion-resistant metal as a container. Examples of such metals include stainless steel and aluminum, with aluminum being preferred due to its light weight and cost.

The following "Examples" illustrate the effects of the present invention in comparison with the prior art, and the present invention is not limited to these "Examples" in any way. In the following, "parts" are "parts by weight" unless otherwise specified.

Example 1 (prior art) 90mg of gamma-type electrolytic manganese dioxide (EMD)
was heated to 375°C for 3 hours. Gamma manganese dioxide is converted to beta manganese dioxide, which is mixed with 6 mg graphite (conductive diluent) and 4 mg
of polytetrafluoroethylene (PTFE) dispersion (binder). The mixture was formed into a pellet approximately 1 inch (2.54 cm) in diameter and heated to 300°C under vacuum for 6 hours. This cathode pellet was combined with a lithium foil disc (70 mg) anode, a nonwoven polypropylene separator, and approximately 275 mg of 1M LiClO ₄ in an equal volume mixture of PC/DME.
Along with the electrolyte solution, a flat wafer battery (height
0.254cm x diameter 2.54cm). The open circuit voltage of this battery was 3.61 volts. This completed battery
Upon heating to 115° C. for 1 hour and then cooling to room temperature, an expansion of 0.003 inches was observed. A second cell was similarly constructed and showed no appreciable expansion when stored at room temperature for 45 days.

Example 2 (Modification of Prior Art) A cell was made as in Example 1 above, but in this example the cathode pellet was heated to 150°C instead of 300°C. When a battery is heated to 150°C for 1 hour and then cooled to room temperature, the expansion is approximately 0.040 inches (0.10
cm). A second cell made as described above expanded approximately 0.010 inches (0.0254 cm) when stored at room temperature for 45 days.

Example 3 (Invention) A mixture of 90 mg of gamma manganese dioxide and 1 mg of lithium nitrate dissolved in 25 ml of water was dried to evaporate the water. The gamma manganese dioxide from which lithium nitrate had been precipitated was then heated at 375°C for 3 hours. The raw material thus obtained is 6
mg of graphite and 4 mg of PTFE dispersion, which was formed into cathode pellets as in Example 1 and heated under reduced pressure at 150° C. for 6 hours. When this pellet was assembled into a battery as in Example 1, the open circuit voltage was 3.49 volts. battery to 115℃
When heated for 1 hour at room temperature and then cooled to room temperature, the cell expanded approximately 0.010 inches (0.0254 cm). A second cell was made as described above and showed no appreciable expansion when stored at room temperature for 45 days. When discharged, the capacity of these cells was essentially the same as that of the cells of Example 1 (first and second) (approximately 90% of the theoretical capacity value at low currents).
%).

Example 4 (Invention) A battery was made using the materials and procedures of Example 3, but in this example calcium nitrate (1) was used instead of lithium nitrate.
mg) and the mixture was heated to 390°C.
When the battery was heated at 115°C for 1 hour and cooled to room temperature, the battery expanded approximately 0.020 inches (0.0508 cm).
It was hot.

It can be seen that the open circuit voltage in Example 3 is somewhat lower than in the cells of Examples 1 and 2 (prior art). This low open circuit voltage indicates a deactivated surface area of the cathode. Such open circuit voltage differences, however, do not significantly adversely affect battery performance during actual discharge.

It will be appreciated that various modifications are possible in the materials and operations in the construction of the cathodes and cells of the present invention. The above examples are given for the purpose of illustrating the present invention, and the present invention is not limited thereby.

Claims (1)

[Scope of Claims] 1. A stabilized non-aqueous chemical cell comprising an active metal anode, a cathode consisting of a cathode active material having active surface functional groups, and a non-aqueous electrolyte solvent containing an electrolyte salt dissolved therein. A method of manufacturing said stabilized cathode, comprising partially deactivating substantially all of the active surface of the cathode by reacting an inorganic additive with said cathode active material prior to initial cell discharge. A method for manufacturing a non-aqueous chemical battery. 2. Claims characterized in that such partial deactivation is effected by the inclusion within the cathode of an inorganic additive that reacts with active surface functional groups on the cathode and converts them to a less active state. The method described in item 1. 3. A method according to claim 1, characterized in that such partial deactivation is accomplished by including in the cell an inorganic additive which reacts with the cathode and causes the cathode to partially discharge at its surface. 4 The inorganic additive is present in the cathode in an amount up to 5% by weight of the weight of the cathode.
Or the method described in Section 3. 5 The cathode is prepared by mixing a cathode active material with an inorganic additive that reacts with the surface functional groups of the active material to deactivate those functional groups, and heating the inorganic additive to initiate the reaction. 2. A method as claimed in claim 1, characterized in that it is produced by the steps of partially deactivating the active surface of the cathode, and subsequently shaping the cathode. 6. The method of claim 5, wherein the inorganic additive constitutes up to 5% by weight of the mixture of cathode active material and the inorganic additive. 7. The method of claim 5, wherein the cathode active material comprises electrolytic gamma manganese dioxide, and the gamma manganese dioxide is converted to beta manganese dioxide during heating of the inorganic additive. 8. The method of claim 7, wherein the inorganic additive is selected from the group consisting of alkali and alkaline earth metal nitrates and nitrites. 9. The method of claim 8, wherein the inorganic additive is selected from the group consisting of lithium nitrate and calcium nitrate. 10. The method according to claim 9, wherein the inorganic additive is lithium nitrate. 11. The method according to claim 7, wherein the non-aqueous electrolyte solution is easily oxidized and decomposed to generate gas. 12. The method according to claim 11, wherein the electrolyte solution comprises propylene carbonate.