Lithium-Metal Battery Electrolyte and Density Control for Cycle Life
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Solution Overview
Problem
Lithium-metal secondary batteries face issues with uneven lithium deposition, increased electrolyte decomposition, and poor charge-discharge cycle characteristics due to expansion and contraction of electrodes, particularly when using highly concentrated electrolytes.
Innovation Solution
Control the deposition morphology of lithium by adjusting the relative density of the lithium metal layer within specific ranges (40-85% or 70-95%) and using highly reduction-resistant or oxidation-resistant electrolytic solutions, combined with controlled charge-discharge cycles under confined pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a space having 100 to 120% the thickness in which lithium is theoretically deposited is provided between a negative electrode and a separator, then expansion and contraction of electrodes can be eased, but lithium deposition becomes uneven and the contact area with electrolytic solution is increased leading to increased electrolyte decomposition
Solution Approach 1:
The invention changes the physical state and concentration parameters of the electrolyte by using a highly concentrated electrolytic solution (4-6 mol/L LiFSI) with specific solvent composition (ether-based and/or carbonic acid ester-based solvents in controlled ratios). This parameter change allows the electrolyte to maintain stability even when lithium deposits unevenly, reducing decomposition despite increased contact area.
2Reliability
If a highly concentrated electrolytic solution containing about 4 to 6 mol of LiFSI per L of organic solvent is used, then oxidation-reduction stability of the electrolytic solution can be improved, but lithium ions near the positive electrode rapidly decrease in discharge reactions leading to poor charge-discharge cycle characteristics
Solution Approach 1:
The invention uses a composite electrolytic solution system combining multiple solvent types (ether-based and carbonic acid ester-based solvents) in specific proportions. This composite approach balances the oxidation-reduction stability provided by high concentration LiFSI with the lithium ion transport efficiency needed for good cycle characteristics, creating a synergistic electrolyte composition.
3Quantity of substance
If carbonic acid esters are used in the electrolytic solution, then the electrolyte can dissolve lithium salts effectively, but carbonic acid esters easily react with lithium metal increasing electrolyte decomposition
Solution Approach 1:
The invention applies local quality control by limiting the concentration of carbonic acid ester-based solvents to specific ranges (5-50 vol% in certain embodiments) within the overall electrolyte composition. This localized control of solvent quality allows effective lithium salt dissolution while minimizing the harmful reaction between carbonic acid esters and lithium metal.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Improves charge-discharge cycle characteristics by suppressing electrolyte decomposition and maintaining optimal lithium ion concentrations, enhancing energy efficiency.
Implementation Method 1
the proportion of the amount of redissolution of lithium with respect to the amount lithium deposited on the copper surface
Implementation Method 2
a highly reduction-resistant electrolytic solution, including 2 to 6 mol of electrolyte per L of solvent
Data Source
AI summary
A lithium-metal secondary battery, which includes a highly reduction-resistant electrolytic solution, including 2 to 6 mol of electrolyte per L of solvent and also having a lithium deposition dissolution efficiency of 98.5% or more, which lithium deposition dissolution efficiency is the proportion of the amount of redissolution of lithium to the amount thereof deposited on the copper surface, wherein the relative density of a lithium metal layer in a negative electrode is 40 to 85%. In addition, a lithium-metal secondary battery, which includes a highly oxidation-resistant electrolytic solution, including 2 to 6 mol of electrolyte per L of solvent and also having a voltage of 5.5 V or more when the current density is 0.4 mA/cm2 using lithium as a counter electrode and platinum as a working electrode, wherein the relative density of a lithium metal layer in a negative electrode is 70 to 95%.