Sulfur-Modified Cathode Material for Li-Ion Cycle Capacity Retention
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Solution Overview
Problem
Existing lithium ion secondary batteries face challenges in achieving increased discharge capacity and maintaining excellent cycle characteristics due to the reduction in charge and discharge capacity during repeated cycles.
Innovation Solution
A sulfur-containing material for positive electrode active materials, including a sulfur-modified compound, is used with a discharge end potential less than 1.0 V (Li+/Li) and a charge end potential between 3.1 V(Li+/Li) to 5.0 V(Li+/Li), along with a composition for forming a positive electrode active material layer containing a sulfur-modified compound and optional additives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional active materials are used in the positive electrode, then the battery structure is simple and ease of manufacture is maintained, but the discharge capacity is insufficient and cycle characteristics deteriorate due to capacity reduction during repeated cycles
Solution Approach 1:
The patent employs a composite material system consisting of sulfur-modified polyacrylonitrile as the active material, combined with specific binders (carboxymethyl cellulose and styrene-butadiene rubber) and conductive agents (acetylene black). This composite structure achieves both high discharge capacity (940 mAh/g at 0.2C rate) and excellent cycle characteristics (96% capacity retention after 100 cycles) by synergistically combining the high-capacity sulfur modification with materials that maintain structural integrity during cycling
Solution Approach 2:
The patent optimizes multiple parameters including the sulfur content (10-80 mass%), binder ratios (CMC:SB = 1:4 to 4:1), and discharge end potential (<1.0 V vs. Li+/Li). By systematically adjusting these parameters, the invention achieves peak performance with 48 mass% sulfur content and specific binder ratios, resolving the contradiction between capacity and cycle stability
2Quantity of substance
If the discharge end potential is lowered to increase discharge capacity, then more lithium ions can be extracted and discharge capacity increases, but the electrode structure may become unstable and cycle characteristic deteriorates
Solution Approach 1:
The patent uses carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SB) as intermediary materials that mediate between the sulfur-modified polyacrylonitrile active material and the electrode structure. These binders form a stable matrix that maintains structural integrity even when the discharge end potential is lowered to 0.3 V, preventing electrode disintegration while allowing high discharge capacity (1020 mAh/g at 0.1C rate)
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
The sulfur-containing material enhances discharge capacity and improves cycle characteristics by maintaining charge and discharge capacity over repeated cycles.
Implementation Method 1
a sulfur-containing material for positive electrode active materials of a lithium ion secondary battery, the sulfur-containing material for positive electrode active materials including a sulfur-modified compound
Data Source
AI summary
Provided is a sulfur-containing material for positive electrode active materials of a lithium ion secondary battery, the sulfur-containing material for positive electrode active materials including a sulfur-modified compound. The sulfur-containing material for positive electrode active materials is used such that a discharge end potential of a positive electrode in a charge and discharge cycle of the lithium ion secondary battery is less than 1.0 V(Li+/Li).