Positive Electrode Active Material with Segregated Surface Layer
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges in maintaining capacity and cycle characteristics due to increased charging voltage, leading to reduced reliability and safety.
Innovation Solution
A positive electrode active material with a layered rock-salt crystal structure in the inner region and a rock-salt crystal structure with magnesium, fluorine, and oxygen in the superficial region, aligned to form a stable coating layer, enhancing charge and discharge characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the charging voltage is increased to increase capacity, then the capacity of lithium cobalt oxide increases from 155 mAh/g at 4.3V to 220 mAh/g at 4.6V, but the cycle characteristics deteriorate with capacity retention decreasing from 95% or more to 50% or less after 30 cycles
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the inner core region contains lithium cobalt oxide with layered rock-salt crystal structure for high capacity, while the outer shell region contains magnesium, fluorine, and oxygen with rock-salt crystal structure for stability. This spatial differentiation of material properties allows the battery to achieve both high capacity (220 mAh/g at 4.6V) and good cycle characteristics (90% or more capacity retention after 30 cycles), resolving the contradiction between capacity improvement and cycle stability.
2Power
If the charging voltage is increased to improve power output, then the energy density increases, but the safety and reliability of the battery deteriorate due to reduced cycle life
Solution Approach 1:
The patent employs composite materials by combining lithium cobalt oxide (providing high energy density) with magnesium fluoride-containing compounds (providing structural stability and safety). The composite structure consists of a core region with lithium cobalt oxide and an outer region with magnesium, fluorine, and oxygen in rock-salt crystal structure. This composite approach enables the battery to achieve high energy density while maintaining safety and reliability through the stabilizing effect of the outer shell region.
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 proposed active material structure improves capacity retention, cycle stability, and safety of lithium-ion secondary batteries by suppressing capacity reduction during charge and discharge cycles.
Implementation Method 1
a covering layer which is formed on a superficial portion of the positive electrode active material by segregation
Data Source
AI summary
Provided is a positive electrode active material which suppresses a reduction in capacity due to charge and discharge cycles when used in a lithium ion secondary battery. A covering layer is formed by segregation on a superficial portion of the positive electrode active material. The positive electrode active material includes a first region and a second region. The first region exists in an inner portion of the positive electrode active material. The second region exists in a superficial portion of the positive electrode active material and part of the inner portion thereof. The first region includes lithium, a transition metal, and oxygen. The second region includes magnesium, fluorine, and oxygen.