Core-Shell Cathode Material to Limit Mn Dissolution in LiMnPO4 Batteries
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Solution Overview
Problem
Lithium manganese phosphate positive electrode active materials in secondary batteries suffer from Li/Mn anti-site defects and significant manganese dissolution during charge and discharge, leading to reduced capacity, safety issues, and poor cycling performance.
Innovation Solution
A core-shell structured positive electrode active material is developed, comprising a doped lithium manganese phosphate core and three coating layers: a crystalline pyrophosphate, an oxide, and a carbon layer, which reduces Li/Mn anti-site defects and manganese dissolution, enhancing structural stability and reducing interfacial reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium manganese phosphate is used as positive electrode active material, then the secondary battery can achieve basic energy storage function, but Li/Mn anti-site defects and manganese dissolution occur during charge and discharge, leading to reduced capacity and poor cycling performance
Solution Approach 1:
The positive electrode active material is divided into a core region (lithium manganese phosphate) and a shell region (doped lithium manganese phosphate), where the shell surrounds and protects the core. This segmentation prevents direct contact between the core and electrolyte, reducing manganese dissolution while maintaining the electrochemical activity of the core material.
Solution Approach 2:
Doping elements (such as Al, Mg, Nb, Mo, W) are introduced into the shell region to create local compositional differences. The doped shell has enhanced structural stability and reduced manganese dissolution compared to the undoped core, providing localized protection where it is most needed at the electrode-electrolyte interface.
2Quantity of substance
If lithium manganese phosphate is used as positive electrode active material, then the battery can operate, but significant manganese dissolution occurs during charge and discharge, leading to reduced capacity
Solution Approach 1:
The doped shell is formed around the lithium manganese phosphate core before the electrode is assembled and before any charge-discharge cycles occur. This preliminary protective layer prevents manganese dissolution from the outset, maintaining the quantity of active manganese in the electrode throughout the battery's operational life.
3Reliability
If lithium manganese phosphate is used as positive electrode active material, then energy storage is achieved, but safety performance deteriorates due to manganese dissolution and structural degradation
Solution Approach 1:
The positive electrode active material is designed as a composite structure combining lithium manganese phosphate core with a doped lithium manganese phosphate shell. This composite structure leverages the high capacity of the core material while the doped shell provides enhanced structural stability and safety, preventing catastrophic failure during operation.
Data Source
AI summary
Provided are a positive electrode active material and a preparation method thereof, a positive electrode plate, a secondary battery, a battery module, a battery pack, and an electric apparatus. The positive electrode active material includes a core containing LimAxMn1-yByP1-zCzO4-nDn, a first coating layer enveloping the core and containing a crystalline pyrophosphate LiaMP2O7 and/or Mb(P2O7)c, a second coating layer enveloping the first coating layer and containing an oxide M′dOe, and a third coating layer enveloping the second coating layer and containing carbon. The positive electrode active material of this application can reduce Li/Mn anti-site defects produced, reduce dissolving-out amount of manganese, lower the lattice change rate, increase the capacity of the secondary battery, and improve the cycling performance, high-temperature storage performance, and safety performance of the secondary battery.