Li-Ion Cathode Surface Roughness and Electrolyte for Temperature Range
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Solution Overview
Problem
Lithium ion secondary batteries using monolithic positive electrode active materials face challenges in maintaining good cycle characteristics at high temperatures and preventing a decrease in rate performance at low temperatures.
Innovation Solution
A lithium ion secondary battery with a positive electrode active material layer surface roughness (Ra) less than 1.0×10^4 Å and a nonaqueous electrolyte solution containing specific additives, such as compounds with halogen-boron or halogen-phosphorus bonds, enhances both high-temperature cycle characteristics and low-temperature rate performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a monolithic positive electrode active material is used, then cycling stability is improved, but rate performance at low temperature deteriorates
Solution Approach 1:
The patent applies local quality by creating a dual-structure positive electrode where monolithic particles (providing stability) are combined with secondary particles formed by agglomeration (providing rate performance). The secondary particle structure creates local regions with different functional characteristics - the core monolithic particles maintain structural integrity while the outer agglomerated structure facilitates ion transport, thus resolving the contradiction between cycling stability and rate performance.
Solution Approach 2:
The patent uses composite materials by combining monolithic positive electrode active material particles with binding agents and conductive materials to form a secondary particle structure. This composite approach allows the battery to benefit from both the high stability of monolithic particles and the enhanced rate performance of the agglomerated secondary particle morphology, effectively resolving the performance contradiction.
2Reliability
If surface roughness is reduced, then high-temperature cycle characteristic is improved, but low-temperature rate performance deteriorates
Solution Approach 1:
The patent applies parameter changes by optimizing the surface roughness within a specific range (0.3 μm to 3.0 μm) rather than simply minimizing it. This controlled surface roughness provides sufficient active material surface area for good low-temperature rate performance while maintaining smooth enough surfaces to prevent microcrack formation at high temperatures, thus resolving the contradiction between high-temperature cycle characteristic and low-temperature rate performance.
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 battery achieves improved cycle characteristics under severe conditions exceeding 50°C and maintains rate performance at 0°C by preventing microcracks and forming a conductive path through electrode coatings.
Implementation Method 1
forming a conductive path through electrode coatings
Implementation Method 2
by setting a surface of the positive electrode to specific surface roughness (Ra)... prevents microcracks
Data Source
AI summary
The present disclosure provides a lithium ion secondary battery, in which surface roughness (Ra) of a surface of a positive electrode active material layer containing a positive electrode active material is less than 1.0×104 Å, and the lithium ion secondary battery includes 5 a nonaqueous electrolyte solution containing at least one selected from the group consisting of compounds of Formulas (1) to (10) described in the specification.