Spinel LiMn2O4 Cathode Coating for Crack-Induced Capacity Fade
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries using lithium manganese oxide with a spinel type crystal structure face capacity deterioration due to manganese dissolution from cracked particles caused by increased density through press treatment, despite efforts to enhance energy density.
Innovation Solution
A coating film containing a LiMnPO4 component and an F component is formed on the surface of cracked lithium manganese oxide particles by initial charging at high voltage, suppressing manganese dissolution and enhancing capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the positive electrode active material layer is increased in density by press treatment, then energy density is improved, but cracks are caused in lithium manganese oxide particles leading to capacity deterioration
Solution Approach 1:
A coating film including phosphorus is formed on the lithium manganese oxide particle surface before press treatment. This preliminary coating prevents crack formation during densification by providing a protective layer that accommodates stress, allowing the particle to be densified without capacity deterioration.
Solution Approach 2:
The invention uses a composite structure where a phosphorus-containing coating film is combined with lithium manganese oxide core particles. This composite material approach allows the beneficial properties of both materials: the core provides high capacity while the coating provides crack resistance during press treatment.
2Reliability
If a coating film including phosphorus is provided on lithium manganese oxide particles, then capacity deterioration due to Mn dissolution is suppressed, but the energy density is reduced
Solution Approach 1:
The invention optimizes the coating film thickness and phosphorus content to achieve a balance between protection and energy density. By controlling the coating parameters, sufficient protection against Mn dissolution is provided while minimizing the volume occupied by the coating material.
Solution Approach 2:
The coating film is applied selectively on the particle surface where it is most needed for protection, rather than uniformly throughout the entire particle structure. This localized approach maximizes protective effect while minimizing impact on overall energy density.
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 coating film effectively prevents capacity deterioration during repeated charging and discharging, allowing for high energy density and improved cycle life of the battery.
Implementation Method 1
a coating film capable of suppressing dissolution of Mn can be formed on the whole particle including the cracked part
Implementation Method 2
a positive electrode active material layer including a positive electrode active material is subjected to a press treatment... initial charging at high voltage... a coating film... can be formed
Data Source
AI summary
A nonaqueous electrolyte secondary battery is provided which is suppressed in capacity deterioration upon repeating charging and discharging irrespective of cracks being formed in a lithium manganese oxide particle having a spinel type crystal structure. The nonaqueous electrolyte secondary battery herein disclosed includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. The positive electrode includes a positive electrode active material layer. The positive electrode active material layer includes lithium manganese oxide particles having a spinel type crystal structure as the positive electrode active material. At least a part of the lithium manganese oxide particles has a cracked part. The lithium manganese oxide particles have a coating film on the particle surface including the surface of the cracked part. The coating film contains a P component including a LiMnPO4 component, and a F component.