Core-Shell Cathode Material for Lithium Battery Safety
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Solution Overview
Problem
Lithium secondary batteries face challenges with insufficient safety, particularly in thermal stability and overcharging characteristics, due to limitations in existing cathode active materials like lithium cobalt oxide, lithium nickel oxide, and olivine-type ferric phosphate lithium compounds, which compromise their high capacity and energy density demands.
Innovation Solution
A cathode active material is developed with a lithium metal oxide secondary particle core coated with barium titanate and olivine-type ferric phosphate lithium oxide, enhancing thermal stability and overcharging safety through a dry-coating process that maintains excellent electric characteristics and productivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium cobalt oxide, lithium nickel oxide, or lithium metal composite oxide is used as cathode active material, then basic battery characteristics are achieved, but safety is insufficient particularly in thermal stability and overcharging characteristics
Solution Approach 1:
The patent applies composite materials by combining lithium cobalt oxide core particles with a shell layer comprising lithium nickel composite oxide and lithium manganese oxide. This composite structure integrates the high capacity of lithium cobalt oxide with the thermal stability of lithium manganese oxide, achieving improved safety without sacrificing battery characteristics. The composite material approach allows the cathode to exhibit both high discharge capacity and enhanced thermal stability.
Solution Approach 2:
The patent implements local quality by creating a core-shell structure where different regions have different compositions and functions. The core region contains lithium cobalt oxide for high capacity, while the shell region contains lithium nickel composite oxide and lithium manganese oxide for thermal stability and safety. This spatial differentiation of material properties allows simultaneous optimization of capacity and safety characteristics.
2Reliability
If various safety means such as shutdown functions, electrolyte additives, and PTC devices are introduced, then safety is improved, but these means are designed under the condition that cathode active material is not filled to a high level, so if filled to high level for high capacity, safety means tend to be operated inappropriately and safety deteriorates
Solution Approach 1:
The patent applies preliminary action by incorporating safety-enhancing materials (lithium manganese oxide and lithium nickel composite oxide) directly into the cathode active material structure before battery assembly. This pre-integration of safety functions into the cathode material itself ensures that safety characteristics are maintained even at high filling levels, eliminating the need for separate safety devices that may fail at high capacity densities.
3Reliability
If spinel-type lithium manganese oxide is used, then low price and high safety are achieved, but energy density gradually deteriorates
Solution Approach 1:
The patent merges lithium cobalt oxide (high energy density) with lithium manganese oxide (high safety, low cost) in a core-shell composite structure. This combination allows the cathode material to simultaneously achieve high energy density from the lithium cobalt oxide core and high safety from the lithium manganese oxide shell, resolving the trade-off between energy density and safety.
4Reliability
If olivine-type ferric phosphate lithium compound is used, then low price and high safety are achieved, but electron conductivity is very low and average operating potential is low, so high capacity demands are not satisfied
Solution Approach 1:
The patent applies local quality by placing olivine-type ferric phosphate lithium compound specifically in the shell region of the core-shell structure, where it provides safety benefits without dominating the overall electrochemical performance. The core region maintains lithium cobalt oxide for high power and conductivity, while the shell provides safety enhancement, achieving local optimization of both safety and electric characteristics.
Data Source
Figure 1(a)~1(d)
Figure 2(a)~2(e)
Figure 3~4
AI summary
A cathode active material for a lithium secondary battery includes a lithium metal oxide secondary particle core formed by agglomerating lithium metal oxide primary particles; and a shell formed by coating the secondary particle core with barium titanate and metal oxide. This cathode active material allows making a lithium secondary battery having improved safety, particularly in thermal stability and overcharging characteristics.