JP-7856062-B2 - Non-aqueous secondary battery

Inventors

• 坪内 洋

Assignees

• トヨタ自動車株式会社

Dates

Publication Date

20260511

Application Date

20230703

Claims (3)

1. Positive electrode and, Lithium metal anode and A non-aqueous secondary battery comprising an electrolyte, The electrolyte contains a pyrrolidinium cation and a bis(fluorosulfonyl)imide anion (FSI), The molar ratio of lithium ions to the pyrrolidinium cation is 10 to 40. The molar concentration of the bis(fluorosulfonyl)imide anion is 3 to 4 mol/L. The electrolyte comprises dimethoxyethane, LiFSI as an electrolyte, and Pyr13-FSI or Pyr14-FSI as an ionic liquid. A non-aqueous secondary battery characterized by the following features.
2. The non-aqueous secondary battery according to claim 1, wherein the pyrrolidinium cation is 1-methyl-1-propylpyrrolidinium cation (Pyr13) or 1-butyl-1-methylpyrrolidinium cation (Pyr14).
3. The non-aqueous secondary battery according to claim 1 or 2 , wherein the content ratio of the ionic liquid in the electrolyte is 0.93 to 2.78% by mass.

Description

This disclosure relates to non-aqueous secondary batteries. With the widespread use of small mobile devices such as cell phones and laptops, there has been a lot of development going on in non-aqueous rechargeable batteries that can be repeatedly charged and discharged. Patent Document 1 discloses a rechargeable lithium battery in which a high-salt-concentration electrolyte has a lithium-imide salt concentration of at least 2 moles per liter of organic solvent as the electrolyte for the lithium metal anode. Special table 2018-505538 publication The following describes in detail specific embodiments to which this disclosure applies. However, the present invention is not limited to the following embodiments. The following factors are considered to be the causes of a decrease in the cycle capacity retention rate (discharge capacity retention rate) of non-aqueous secondary batteries (non-aqueous lithium-ion secondary batteries), or in other words, a decrease in charge-discharge efficiency. These factors include irreversible reactions of lithium metal, namely charge consumption due to electrolyte decomposition, charge consumption due to minute short circuits, and electrical isolation of lithium metal. In the rechargeable lithium battery described in Patent Document 1, a high-concentration electrolyte containing a lithium imide salt, specifically lithium bis(fluorosulfonyl)imide (LiN( SO₂ ) ₂ ; hereafter also referred to as LiFSI), is used as the electrolyte for the lithium metal negative electrode. Thus, while electrolytes containing high concentrations of LiFSI exhibit relatively high Li precipitation and dissolution efficiency, there was room for improvement in terms of suppressing electrolyte decomposition. As mentioned above, various factors can contribute to a decrease in cycle capacity retention, but charge consumption due to electrolyte decomposition is considered the main cause. Lithium metal has a very low reaction potential, and the solvent decomposes as it precipitates. Therefore, it is important to reduce the surface area of the precipitated lithium metal to suppress the growth of lithium dendrites (tree-like crystals) and to have a solvation structure that suppresses electrolyte decomposition. Normally, lithium ions in low-salt electrolytes are coordinated with the solvent, and increasing the salt concentration increases the coordination ratio of anions (e.g., FSI, described later). It is known that when anions coordinate with lithium ions, they become more susceptible to reductive decomposition, increasing the proportion of anion-derived film and improving the deposition and dissolution efficiency of the lithium metal anode. On the other hand, as salt concentrations increase, anions are actively decomposed, so there is considered to be a limit to the efficiency improvement achieved through high concentrations. The non-aqueous secondary battery relating to this disclosure (hereinafter also referred to as "this secondary battery") comprises a positive electrode, a lithium metal negative electrode, and a specific electrolyte, and may further comprise a separator. In this secondary battery, the positive electrode, lithium metal negative electrode, and separator can be those conventionally known in the field of non-aqueous secondary batteries, to the extent that the effects of this disclosure can be obtained. Furthermore, this secondary battery contains pyrrolidinium cations and bis(fluorosulfonyl)imide anions (also referred to as FSI) in the electrolyte. In addition, from the viewpoint of improving the discharge capacity retention rate, the molar ratio of lithium ions to pyrrolidinium cations (Li/cation) in the electrolyte is 10 to 40. Also, from the viewpoint of improving the discharge capacity retention rate, the molar concentration of FSI in the electrolyte is 3 to 4 mol/L (M). Thus, in this secondary battery, because specific cations are present in the electrolyte in addition to lithium ions, the charge is dispersed through interaction with the bis(fluorosulfonyl)imide anions coordinated to the lithium ions, thereby suppressing the decomposition of the anions. As a result, the decrease in the discharge capacity maintenance rate can be suppressed. Furthermore, the presence of specific cations in addition to lithium ions can mitigate the concentration of lithium ions due to the steric interference effect of these cations, even if localized current concentration occurs, thereby suppressing the formation of lithium dendrites. As a result, the decrease in discharge capacity maintenance rate can be suppressed. Thus, in this secondary battery, controlling the solvation structure in the electrolyte improves charge-discharge efficiency and enhances the discharge capacity retention rate. In this secondary battery, from the viewpoint of molecular size and intramolecular charge distribution, it is preferable that the pyrrolidinium cation is either a 1-methyl-1-propylpyrrolidinium cation (Pyr13) or a 1-butyl-1-