Non-aqueous electrolyte type lithium ion secondary cell
There is provided a lithium ion secondary cell excellent in charging and discharging cycle characteristics. A lithium ion secondary cell includes: an electrode body including a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a separator; and a non-aqueous electrolyte containing a lithium salt as a supporting salt in an organic solvent, the electrode body and the non-aqueous electrolyte being accommodated in a case. The positive electrode active material is a lithium transition metal oxide having a layered structure. The electrolyte contains a compound represented by a chemical formula (I) in an amount of β mol relative to the total content α mol of moisture to be mixed in the cell. β satisfies −1.3≦log(β/α)≦1.
1. A method for manufacturing a lithium ion secondary cell, wherein the lithium ion secondary cell comprises:
an electrode body including a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a separator, as constituent members; and a non-aqueous electrolyte containing a lithium salt as a supporting salt in an organic solvent, the electrode body and the non-aqueous electrolyte being accommodated in a case, the method comprising:
(a) preparing the positive electrode, the negative electrode, the separator, and an initial electrolyte serving as constituent members of the cell, the positive electrode active material including, as a main component, a layered oxide containing lithium and a transition metal as constituent metal elements, the initial electrolyte including, as a supporting salt, a lithium salt containing fluorine as a constituent atom, and the supporting salt being dissolved in an organic solvent in a prescribed concentration;
(b) ascertaining, based on the content of moisture contained in the positive electrode, the negative electrode, the separator, and the initial electrolyte prepared in the step (a), a molar equivalent value α of the total content of moisture to be mixed in the case due to the constituent members;
(c) substituting a value of the α into the following mathematical expression (A), and calculating a numerical value range of β satisfying the mathematical expression (A)
−1.3≦log(β/α)≦1 (A)
wherein α represents the total number of moles of moisture to be mixed in the case when the cell is assembled;
(d) adding as an additive, a compound represented by the following chemical formula (I):
in a number of moles within the numerical value range of the β calculated in the step (c) to the initial electrolyte, and preparing a final electrolyte; and
(e) assembling a lithium ion secondary cell under an environment with a dew point of −10° C. or less using the positive electrode, the negative electrode, the separator, and the final electrolyte.
2. The method for manufacturing according to claim 1 , wherein a numerical value range of the β satisfies −0.5≦log(β/α)≦0.6.
3. The method according to claim 1 , wherein the negative electrode active material comprises carbon material.
4. The method according to claim 1 , wherein the supporting salt is at least one chosen from LiPF 6 , LiBF 4 , LiAsF 6 , and LiSbF 6 .
5. The method according to claim 1 , wherein in step (e), the dew point ranges from −20° C. to −50° C.