Li2S Positive Electrode for All-Solid Battery
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Solution Overview
Problem
Lithium secondary batteries face challenges in achieving high charge-discharge capacity due to the low ionic conductivity of Li2S as a positive electrode active material, necessitating the use of conductive components like acetylene black and Li2S.P2S5, but there is a desire to maximize the proportion of Li2S for improved performance.
Innovation Solution
The use of Li2S or Na2S complexed with lithium or sodium salts, such as LiI, LiBr, or NaI, as the positive electrode active material, combined with mechanical milling treatment to enhance ionic conductivity and charge-discharge capacity, while maintaining a suitable ratio of A2S to AX and incorporating a carbon-based electrical conducting material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Li2S is used as the positive electrode active material to improve charge-discharge capacity, then the theoretical capacity increases, but the ionic conductivity becomes too low for practical use
Solution Approach 1:
The patent uses composite materials by combining Li2S with conductive components (acetylene black, graphite) and electrolytes (Li2S.P2S5) to create a positive electrode that maintains high Li2S content while achieving sufficient ionic conductivity through the synergistic effects of the composite structure
Solution Approach 2:
The patent changes the compositional parameters of the positive electrode, specifically optimizing the ratios of Li2S (20-80 wt%), conductive component (10-50 wt%), and electrolyte (10-50 wt%) to achieve the desired balance between capacity and conductivity. The use of Li2S complexed with lithium salt is identified as a key parameter change that improves conductivity
2Reliability
If conductive components and electrolyte are added to improve ionic conductivity, then the electrical conductivity increases, but the proportion of Li2S active material decreases
Solution Approach 1:
The patent optimizes the weight ratios of components to maximize Li2S content while maintaining functionality. Specifically, Li2S is contained at 20-80 wt% (higher than conventional electrodes), conductive component at 10-50 wt%, and electrolyte at 10-50 wt%, achieving a better balance than prior art
Solution Approach 2:
The electrolyte Li2S.P2S5 serves dual functions: it provides ionic conductivity and also acts as a binding matrix that holds the active material and conductive components together, reducing the need for additional binder materials that would further reduce Li2S content
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
This approach results in an all-solid secondary battery with improved charge-discharge capacity, higher ionic conductivity, and a higher proportion of Li2S or Na2S, achieving a balanced performance without compromising on safety and efficiency.
Implementation Method 1
subjecting A2S and AX to mechanical milling treatment in order to obtain A2S.AX
Data Source
AI summary
A positive electrode for an all-solid secondary battery, comprising a positive electrode active material expressed by A2S.AX, whereinA is an alkali metal; andX is selected from I, Br, Cl, F, BF4, BH4, SO4, BO3, PO4, O, Se, N, P, As, Sb, PF6, AsF6, ClO4, NO3, CO3, CF3SO3, CF3COO, N(SO2F)2 and N(CF3SO2)2.