NONAQUEOUS ELECTROLYTE SECONDARY BATTERY

To provide a nonaqueous electrolyte secondary battery, which is capable of suppressing gas generation in a high-temperature environment and which has excellent charge/discharge characteristics in a high-temperature and low-temperature environment.SOLUTION: There is provided a nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode and a nonaqueous electrolyte. The positive electrode includes a positive electrode layer containing, as a positive electrode active material, a lithium-nickel-cobalt-manganese composite oxide. The negative electrode includes a negative electrode layer containing, as a negative electrode active material, a lithium-titanium composite oxide. The nonaqueous electrolyte contains: a nonaqueous solvent containing PC, DMC and MEC in a volume ratio of 1.6-2.4:4.0-4.4:3.6-4.0; an electrolyte containing LiPF6 or LiBF4, the content of the electrolyte being 1.0 mol/L or more and 1.3 mol/L or less with respect to the nonaqueous solvent; and an additive comprising LiPO2F2. When the concentration of the additive is 0.5 wt.% or more and 1.0 wt.% or less with respect to the total amount of the nonaqueous solvent and the electrolyte, the capacity ratio (Y/X) of the capacity (X) of the positive electrode and the capacity (Y) of the negative electrode in initial charge is 0.80 or more and 0.85 or less.SELECTED DRAWING: Figure 1 【課題】 高温環境下でのガス発生を抑制でき、高温及び低温環境下において優れた充放電特性を有する非水電解質二次電池を提供する。【解決手段】 正極、負極、及び非水電解質を備えた非水電解質二次電池を提供する。正極は、リチウムニッケルコバルトマンガン系複合酸化物を正極活物質として含む正極層を備える。負極は、リチウムチタン系複合酸化物を負極活物質として含む負極層を備える。非水電解質は、ＰＣ、ＤＭＣ、及びＭＥＣを１．６～２．４：４．０～４．４：３．６～４．０の体積比で含む非水溶媒；ＬｉＰＦ６又はＬｉＢＦ４を含み、濃度が非水溶媒に対して１．０ｍоｌ／Ｌ以上１．３ｍоｌ／Ｌ以下である電解質；ＬｉＰＯ２Ｆ２からなる添加剤；を含む。添加剤の濃度が非水溶媒と電解質の合量に対して０．５重量％以上１．０重量％以下であるとき、初回充電時の前記正極の容量（Ｘ）と前記負極の容量（Ｙ）の容量比（Ｙ／Ｘ）は、０．８０以上０．８５以下である。【選択図】図１