Four-Layer LiMnPO4 Cathode Coating for Manganese Dissolution Control
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Solution Overview
Problem
Lithium manganese phosphate positive electrode active materials in secondary batteries suffer from manganese ion dissolution during charging and discharging, leading to capacity decay and safety concerns due to interfacial side reactions and gas production.
Innovation Solution
A core-shell structured positive electrode active material is developed, featuring an inner core with a chemical formula of Li1+xMn1−yAyP1−zRzO4 coated with multiple layers, including crystalline pyrophosphate, phosphate, carbon, and a polymer layer, which reduces manganese ion dissolution and lattice change rates, enhancing cycling, rate, and safety performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium manganese phosphate is used as positive electrode active material, then high capacity and abundant raw materials are achieved, but manganese ion dissolution occurs during charging leading to rapid capacity decay
Solution Approach 1:
The patent applies composite materials by creating a core-shell structure where lithium manganese phosphate core is coated with lithium iron phosphate shell. This composite structure combines the high capacity advantage of lithium manganese phosphate with the stability and safety of lithium iron phosphate, preventing manganese ion dissolution while maintaining high capacity performance.
Solution Approach 2:
The patent applies local quality by modifying only the surface region of the lithium manganese phosphate particles with a lithium iron phosphate coating layer. The core retains the original lithium manganese phosphate composition for high capacity, while the shell provides protective functions against manganese dissolution and interfacial side reactions, achieving localized functional differentiation.
2Quantity of substance
If lithium manganese phosphate is used as positive electrode active material, then high capacity is achieved, but interfacial side reactions and gas production occur leading to safety concerns
Solution Approach 1:
The lithium iron phosphate coating layer acts as an intermediary between the lithium manganese phosphate core and the electrolyte. This intermediate shell prevents direct contact between the core and electrolyte, blocking interfacial side reactions and gas production while allowing lithium ion transport, thus improving safety without compromising capacity.
Solution Approach 2:
The composite core-shell structure combines materials with complementary properties: lithium manganese phosphate provides high capacity while lithium iron phosphate provides safety and stability. The composite material approach allows simultaneous achievement of high capacity and improved safety performance.
3Ease of manufacture
If lithium manganese phosphate is used as positive electrode active material, then abundant raw materials are achieved, but good comprehensive performance is not obtained due to manganese ion dissolution
Solution Approach 1:
The patent uses composite materials to combine lithium manganese phosphate (abundant raw materials, high capacity) with lithium iron phosphate (good stability). This composite approach maintains the ease of manufacture advantage from abundant raw materials while achieving good comprehensive performance through the synergistic effects of the two materials.
Data Source
AI summary
A positive electrode active material has a core-shell structure including an inner core and a shell coating the inner core. The inner core has a chemical formula of Li1+xMn1−yAyP1−zRzO4. The shell includes a first coating layer coating the inner core, a second coating layer coating the first coating layer, a third coating layer coating the second coating layer, and a fourth coating layer coating the third coating layer.