JPS6129101B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to high energy electrochemical power cells. In particular, the present invention relates to cells having an oxidizable anode material and a liquid active cathode material and a solid current collector. Recently, there has been a rapid growth in portable electronic products that require batteries for energy supply. Examples are calculators, cameras and digital watches. However, these products highlight the deficiencies of existing power batteries for the required applications.
For example, digital clocks were developed using silver oxide batteries, and although these clocks are becoming popular, it is now generally accepted that the least developed part of digital clock systems is the power battery. This is where I am. In particular, the energy density of silver batteries is such that it is difficult to produce thin, smart watches with a reasonable operating life. Moreover, this battery has poor storage characteristics, low battery voltage and leakage problems. Considerable research has been conducted into batteries using lithium negative electrodes in an effort to develop batteries that solve one or more of the above problems. There are various types of positive electrodes and electrolytes consisting of solvents and solutes. In fact, there is a wealth of literature on examples of lithium negative electrode batteries using various positive electrodes and electrolytes. The electrical properties of these cells, such as energy per unit volume (called energy density), cell voltage and internal impedance, are very different. Of all the known combinations of lithium negative electrodes and various positive electrodes and electrolytes, the one that is believed to have the highest energy density and lowest internal impedance uses some type of inorganic liquid as an active positive electrode depolarizer. It is used as This type of battery is commonly referred to as a "liquid cathode" battery. Early liquid cathode batteries used liquid sulfur dioxide as the active cathode depolarizer, as described in US Pat. No. 3,567,515. Since sulfur dioxide is not a liquid at room temperature and atmospheric pressure, it has been quite difficult to study its chemistry. Most importantly, sulfur dioxide batteries are dangerous for many consumer applications due to their tendency to explode under certain circumstances. A major advance in the development of liquid cathode batteries was the discovery of a group of inorganic substances, commonly called oxyhalides, that are liquid at room temperature and also function as depolarizers as active cathode depolarizers. . Furthermore, these substances can also be used as electrolyte solvents. Liquid cathode cells using oxyhalides are described in US Pat. No. 3,926,669 and US Pat. No. 1,409,307. At least one oxyhalide, thionyl chloride (SOCl ₂ ), has the general properties described above, while also providing substantial additional energy density. As described in US Pat. No. 3,926,669 and British Patent No. 1,409,307,
The negative electrode is metallic lithium or an alloy of lithium, and the electrolyte is an ionically conductive solute dissolved in a solvent that is also the active positive electrode depolarizer. The solute may be a simple salt or a double salt as long as it produces an ionically conductive solution when dissolved in a solvent. Preferred solutes are complexes of inorganic or organic Lewis acids and inorganic ionizable salts. A prerequisite for being useful is that the salt, whether simple or complex, be compatible with the solvent used and provide an ionically conductive solution. According to Lewis theory, or the electronic concept of acids and bases, many substances that do not contain active hydrogen can act as acids, or electron pair acceptors. US Patent No.
No. 3,542,602 suggests that a complex or double salt formed between a Lewis acid and an ionizable salt is a more stable substance than either component alone. Typical Lewis acids suitable for use in the present invention include aluminum chloride, antimony pentachloride, zirconium tetrachloride, phosphorous pentachloride, boron fluoride,
Includes boron chloride and boron bromide. Ionizable salts useful in combination with Lewis acids include lithium fluoride, lithium chloride, lithium bromide, lithium sulfide, sodium fluoride, sodium chloride, sodium bromide, potassium fluoride, potassium chloride, and potassium bromide. is included. The double salt formed by a Lewis acid and an inorganic ionizable salt may be used as is, or the individual components may be added separately to a solvent to form the salt. One such double salt is, for example, a salt produced by combining aluminum chloride and lithium chloride to obtain lithium aluminum tetrachloride. In addition to a negative electrode, an active positive depolarizer, and an ionically conductive electrolyte, these cells require a current collector. According to GB 1409307, any compatible solid that is substantially electrically conductive and inert in the cell is useful as a positive electrode current collector. This is because the function of the current collector is to enable the positive electrode active material to be in electrical contact with the outside world.
It is desirable to have as much surface contact as possible between the liquid cathode and the current collector. Therefore, porous materials are preferred. This is because porous materials provide a high surface area interface with the liquid cathode material. The current collector may be metallic and may be present in any physical form such as a metal film, screen or pressed powder. Examples of some suitable metal current collectors are provided in the table of the aforementioned US Pat. No. 3,926,669. The current collector can also be made partially or completely of carbon. The embodiment described in GB 1409307 uses graphite. Electrical isolation of the current collector and negative electrode is necessary to ensure that no positive or negative electrode reactions occur unless current flows in the external circuit. A mechanical separator can be used since the current collector is insoluble in the electrolyte and the negative electrode does not spontaneously react with the electrolyte. Materials useful for this function are described in the aforementioned US Pat. No. 3,926,669. Although the various cells described in GB 1409307 and US 3926669 are viable, much of the recent interest has focused on chloride as the active cathode depolarizer and electrolyte solvent. Found in batteries that use thionyl. This arises because thionyl chloride can provide greater energy density and power transmission capability than other oxyhalide systems. However, although thionyl chloride cells were found to be the best performing oxyhalides, these cells fell far short of expectations in terms of energy density and internal impedance. Moreover, thionyl chloride batteries are just as dangerous, if not more dangerous, than sulfur dioxide batteries. As a result, all known efforts to commercialize batteries using this compound have failed. By adding copper to the battery, the present invention
substantially safe while also having the benefits of high energy density and low internal impedance.
It is based on the discovery that batteries can be produced with lithium or calcium negative electrodes and thionyl chloride active positive electrode depolarizers. One objective of the present invention is to improve the known lithium/thionyl chloride batteries to make them safer. Another object of the invention is to provide a lithium/thionyl chloride battery with a higher energy density than described in the literature. A further object of the invention is to provide a lithium/thionyl chloride battery with low internal impedance. These and other objects of the present invention provide a negative electrode selected from the group consisting of lithium and calcium, a current collector comprising a porous carbon body in which particulate copper is dispersed, the current collector being spaced from said negative electrode. , and an ionically conductive solute dissolved in an active positive electrode depolarizer selected from the group consisting of one or more of phosphoryl chloride, suryryl chloride, or thionyl chloride, in chemical and electrical contact with both the current collector and the negative electrode. This can be achieved by a battery consisting of an electrolyte in contact with the electrolyte. As previously mentioned, the present invention is based on the discovery that adding elemental copper to batteries results in substantial improvements in both performance and safety. Although the theoretical explanation for this phenomenon is not clear and the applicant does not intend to limit the invention to any theory,
At least one explanation for the results according to the present invention involves the reaction of copper with elemental sulfur. Some of the different reactions that can occur in prior art cells (there is no conclusive evidence as to which reactions actually occur) are as follows. 3SOCl ₂ +8Li→Li ₂ SO ₃ +6LiCl+2S ...(1) 4SOCl ₂ +8Li→LiS ₂ O ₄ +6LiCl+S ₂ Cl ₂ ...(2) 4SOCl ₂ +8Li→8LiCl+2SO ₂ +2S ...(3) All these reactions require the same amount emits electrical energy. However, reaction formula (1) requires only a small amount of thionyl chloride. Therefore, the energy density of this reaction is higher than other reactions. That is, in the reaction of Reaction Formula (1), more electrical energy can be obtained from a predetermined volume of the chemical than in the case of the reaction of Reaction Formula (2) or (3). 1 Regarding the difference in energy of the battery of the present invention
One possible explanation is that copper first acts as a catalyst to cause high energy density reactions such as those in equation (1) and then combines with elemental sulfur to form copper sulfide. . The significance of the copper-sulfur reaction is related to safety. It is generally believed that elemental sulfur in contact with lithium explodes above a certain temperature, and that this temperature is easily reached by rotating short circuits, reverse charging or other electrical conditions as well as exposure to high ambient temperatures. There is. However, copper sulfide does not react explosively with lithium at any of the temperatures that may be experienced in batteries. This is supported by experimental evidence that batteries made in accordance with the present invention do not explode in environments that would cause prior art batteries to explode. Test results showing the effect of varying the percentage of copper on energy density and internal impedance are shown in Table 1. This data is presented by way of example to enable those skilled in the art to better understand and practice the invention. These data are representative examples for illustration and are not intended to limit the scope of the invention in any way. Each data in Table 1 is for a single disk-shaped current collector,
Nominal internal volume 0.574 cm ³ (0.035 cubic inch) configured in a typical button configuration with negative electrode and separator
This is about the test battery. The electrolyte is lithium aluminum tetrachloride in thionyl chloride.
It is a 1.5M solution. The negative electrode is a lithium disk 1.727 cm (0.680 inch) in diameter and 0.508 mm (0.020 inch) thick. The separator is a commercially available ceramic paper. The current collector is acetylene black. Granular copper was dispersed in acetylene black and then compressed into pellets. The only variable in the cell is the carbon:copper weight ratio.

[Table] The above results were obtained from samples tested shortly after battery fabrication. The general trends shown by the data in Table 1 are accentuated when batteries are stored at elevated temperatures. It goes without saying that the preferred embodiments described above are not intended to limit the scope of the invention. Certainly, copper in more or less fine powder form is useful, and other cell geometries such as spiral wound can also be used in the present invention.

Claims (1)

[Scope of Claims] 1. A negative electrode consisting essentially of a negative electrode selected from the group consisting of lithium and calcium, a carbonaceous current collector spaced apart from said negative electrode, an active selected from the group consisting of phosphoryl chloride, thionyl chloride, and suryryl chloride. A battery comprising an ionically conductive electrolyte comprising an ionically conductive solute dissolved in a positive depolarizer, and copper dispersed in the carbonaceous current collector. 2. A battery according to claim 1, wherein said current collector is a porous carbon body, and said copper is in the form of a fine powder and intimately dispersed in said carbon. 3. The battery of claim 2, wherein the carbon:copper weight ratio is about 1:1 to 10:1.