Double-Clad Lithium Manganese Phosphate Cathode for Mn Stability
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Solution Overview
Problem
Lithium manganese phosphate batteries face issues with manganese ion leaching during charging and discharging, leading to capacity decay and safety concerns due to the Jahn-Teller effect and high surface reactivity, which affects their energy density, rate performance, cycling performance, and safety.
Innovation Solution
A secondary battery design featuring a positive electrode with a core-shell structure, where the core comprises Li1+xMn1−yAyP1−zRzO4 and is clad with pyrophosphate and phosphate layers, and a carbon layer, along with a non-aqueous electrolyte containing specific additives to reduce manganese ion leaching and enhance 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 good safety performance are achieved, but manganese ion leaching occurs during charging leading to rapid capacity decay
Solution Approach 1:
A double-clad structure comprising a first cladding layer of crystalline pyrophosphates and a second cladding layer of phosphate is introduced as an intermediary between the lithium manganese phosphate core and the electrolyte. This intermediate structure prevents direct contact between the active material and electrolyte, thereby suppressing manganese ion leaching while maintaining lithium ion transport channels for high capacity and good cycling performance.
Solution Approach 2:
The positive electrode active material is designed as a composite structure with a lithium manganese phosphate core and a double-clad shell of pyrophosphates and phosphate. This composite material combines the high capacity of lithium manganese phosphate with the protective and conductive properties of the cladding layers, achieving both high capacity and excellent cycling stability.
2Ease of manufacture
If lithium manganese phosphate is used as positive electrode active material, then abundant raw material sources are available, but rapid capacity decay occurs due to manganese ion leaching
Solution Approach 1:
The double-clad structure acts as a protective intermediary that prevents manganese ion dissolution into the electrolyte during storage and cycling. The first cladding layer of crystalline pyrophosphates and second cladding layer of phosphate form a barrier that maintains material integrity over time, enabling long-term storage stability while utilizing readily available raw materials.
3Reliability
If surface cladding is applied to reduce manganese ion leaching, then cycling performance improves, but lithium ion migration may be hindered
Solution Approach 1:
The cladding layers are designed with controlled porosity and crystal structure that allow lithium ion diffusion channels to remain open while blocking manganese ion dissolution pathways. The crystalline pyrophosphate and phosphate structures provide selective transport properties that maintain fast lithium ion kinetics while preventing harmful manganese leaching, thus achieving both improved cycling performance and maintained rate performance.
Solution Approach 2:
The double-clad structure exhibits local quality differentiation where the first cladding layer of pyrophosphates provides primary protection against manganese leaching, while the second cladding layer of phosphate enhances structural stability and maintains lithium ion conductivity. This localized functional differentiation ensures that protection against manganese dissolution does not compromise lithium ion migration speed.
4Quantity of substance
If high energy density is pursued, then capacity increases, but safety performance may deteriorate due to thermal runaway risks
Solution Approach 1:
The double-clad structure serves as a safety intermediary that physically isolates the high-capacity lithium manganese phosphate core from direct contact with the electrolyte and external environment. This intermediate barrier prevents thermal runaway propagation and manganese ion dissolution that could lead to safety issues, enabling high energy density operation with improved 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
This design effectively inhibits manganese ion leaching, improves lithium ion migration, and enhances the battery's energy density, rate performance, cycling performance, and safety by forming a stable interfacial film, thereby maintaining capacity and reducing impedance.
Implementation Method 1
the first additive can react with a trace amount of water in the non-aqueous electrolytic solution to form -NHCOOH
Implementation Method 2
generating a uniform and dense interfacial film on the surface of the negative electrode active material, reducing the reduction reaction of the leached-out manganese ions at the negative electrode
Implementation Method 3
promoting lithium ion's migration, thereby improving the rate performance, cycling performance, storage performance, and safety performance of secondary batteries
Data Source
AI summary
The present application provides a secondary battery, a battery module, a battery pack and an electrical device containing the same. The secondary battery comprises a positive electrode plate, and a non-aqueous electrolytic solution, wherein the positive electrode plate comprises a positive electrode active material with a core-shell structure, and the positive electrode active material comprises a core and a shell covering the core, the core comprises Li1+xMn1−yAyP1−zRzO4, the shell comprises a first cladding layer covering the core and a second cladding layer covering the first cladding layer, and the non-aqueous electrolytic solution comprises a first additive comprising one or more of the compounds shown in Formula 1. The present application enables the secondary battery to simultaneously have high energy density with good rate performance, cycling performance, storage performance and safety performance.O═C═N—R1—N═C═O Formula 1