The present application relates to an electrolytic solution, to a secondary battery that uses the electrolytic solution, and to a battery pack, an electric vehicle, an electric power storage system, an electric power tool, and an electronic apparatus that use the secondary battery.
In recent years, various electronic apparatuses such as mobile phones and personal digital assistants (PDAs) have been widely used, and it has been demanded to further reduce the size and the weight of the electronic apparatuses and to achieve their long life. Accordingly, a battery, in particular, a small and light-weight secondary battery capable of providing high energy density has been developed as an electric power source. In these days, it has been considered to apply such a secondary battery to various applications other than the above-described electronic apparatuses. Typical example of the other applications include battery packs attachably and detachably mounted on electronic apparatuses or the like, electric vehicles such as electric automobiles, electric power storage systems such as home electric power servers, and electric power tools such as electric drills.
Secondary batteries have been proposed that utilizes various charge and discharge principles in order to obtain battery capacity. In particular, secondary batteries that utilize insertion and extraction of electrode reactants and secondary batteries that utilize precipitation and dissolution of electrode reactants have attracted attention, since such secondary batteries achieve higher energy density than batteries such as lead batteries and nickel cadmium batteries.
A secondary battery includes a cathode, an anode, and an electrolytic solution. The electrolytic solution includes a solvent and an electrolyte salt. The electrolytic solution that functions as an intermediate in charge and discharge reactions largely influences performance of the secondary battery. Therefore, in order to improve battery characteristics, it is considered to add various additives to the electrolytic solution.
Specifically, when an oxide-based cathode active material is used, a cyanoacetate ester such as methyl cyanoacetate is used in order to suppress decomposition of the electrolytic solution even when an over voltage of a cathode is increased upon electric charge (for example, see Japanese Unexamined Patent Application Publication No. 2011-071083). In order to improve cycle characteristics, for example, succinonitrile, 1,6-dicyano hexane, or the like is used (for example, see Japanese Unexamined Patent Application Publication No. 2010-225522). In order to improve ion conductivity, cyano ester or chain cyano ester carbonate is used (for example see US Patent Application Publication No. 2005/0123835). The cyano ester is CN—C(CH3)2—O—C(═O)—CH3 or the like, and the chain cyano ester carbonate is CN—C(CH3)2—O—C—(═O)—O—CH3 or the like. In order to retain stable dissolution state of an electrolytic solution, a chain saturated hydrocarbon dinitrile compound or the like is used in which nitrile groups are bonded to both terminals of a chain saturated hydrocarbon compound (for example, see Japanese Unexamined Patent Application Publication No. 2011-154783).