Multilayer-Coated Lithium Manganese Phosphate Cathode for Capacity Fade
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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 fading and safety concerns due to high surface reactivity and interfacial side reactions.
Innovation Solution
A core-shell structured positive electrode active material is developed, comprising an inner core of Li1+xMn1−yAyP1−zRzO4 with specific doping elements and a shell comprising multiple coating layers: a pyrophosphate and phosphate layer, a carbon layer, and a polysiloxane layer, which inhibits manganese ion dissolution and promotes lithium ion migration.
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 material source are achieved, but manganese ion dissolution occurs during charging leading to rapid capacity fading
Solution Approach 1:
The patent applies composite materials by creating a core-shell structure where the inner core is Li1+xMn1−yAyP1−zRzO4 and the shell consists of multiple coating layers including pyrophosphate, phosphate, carbon, and polysiloxane. This composite structure combines the high capacity of lithium manganese phosphate with protective coating layers that prevent manganese ion dissolution, thereby resolving the contradiction between achieving high capacity and preventing capacity fading.
Solution Approach 2:
The patent applies local quality by doping specific elements (A and R) at particular positions within the lithium manganese phosphate crystal structure and applying different coating materials at different layers on the surface. This creates localized modifications that address manganese ion dissolution at the surface while preserving the bulk material's high capacity characteristics.
2Quantity of substance
If lithium manganese phosphate is used as positive electrode active material, then high capacity is achieved, but rapid capacity fading occurs due to manganese ion dissolution
Solution Approach 1:
The multi-layer composite coating structure protects the lithium manganese phosphate core during repeated charging and discharging cycles, preventing manganese ion dissolution that would otherwise lead to capacity fading. This enables the material to maintain its high capacity over extended cycling duration.
Solution Approach 2:
The coating layers are applied in advance to the lithium manganese phosphate surface before electrochemical cycling begins. This preliminary protective action prevents manganese ion dissolution from occurring during subsequent charging and discharging cycles, thereby maintaining cycling performance.
3Ease of manufacture
If lithium manganese phosphate is used as positive electrode active material, then abundant raw material source is achieved, but good safety performance is compromised due to manganese ion dissolution
Solution Approach 1:
The patent combines readily available lithium manganese phosphate with coating materials to create a composite structure. This approach maintains the ease of manufacturing and abundant raw material source advantages while the coating layers prevent manganese ion dissolution that would compromise safety 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 solution significantly enhances the rate performance, cycling performance, and safety of secondary batteries by reducing manganese ion dissolution and surface reactivity, while maintaining high energy density and stability.
Implementation Method 1
the first coating layer comprises a pyrophosphate of MP2O7 and a phosphate of XPO4... effectively inhibit the dissolution of manganese ions during lithium de-intercalation
Implementation Method 2
promoting the migration of lithium ions... improving the rate performance, cycling performance, and safety performance
Implementation Method 3
the third coating layer comprises a polymer and the polymer comprises one or more selected from a polysiloxane with a linear structure and a polysiloxane with a cyclic structure... reducing manganese ion dissolution and surface reactivity
Data Source
AI summary
A positive electrode active material and a preparation method therefor, a positive electrode plate containing same, a secondary battery, and a power consuming device are provided. The positive electrode active material has a core-shell structure, comprising an inner core and a shell coating the inner core, wherein the inner core comprises Li1+xMn1−yAyP1−zRzO4, and the shell comprises a first coating layer coating the inner core, and a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer. The positive electrode active material of the present application enables the secondary battery to have a higher energy density, and a good rate performance, cycling performance and safety performance.