Double Shell Cathode Material for Lithium Battery Safety
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Solution Overview
Problem
Lithium secondary batteries face challenges with safety, particularly thermal stability and overcharge characteristics, especially when increasing the capacity of cathode active materials, which often results in deteriorated safety mechanisms and suboptimal performance.
Innovation Solution
A cathode active material with a double shell structure is developed, comprising a lithium metal oxide core coated with a first shell of barium titanate and metal oxide particles for improved thermal stability, and a second shell of olivine-type lithium iron phosphate and conductive material particles for enhanced overcharge safety and discharge characteristics, using a dry-coating method for effective and reproducible production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the filling capability of cathode active material is increased to meet high capacity demand, then energy density is improved, but safety mechanism operation becomes insufficient and safety deteriorates
Solution Approach 1:
A safety mechanism layer comprising lithium iron phosphate and conductive carbon is formed on the surface of the cathode active material particles before battery assembly. This preliminary protective coating ensures that safety mechanisms are already in place and can operate effectively even when the cathode has high filling capability, preventing safety deterioration that would normally occur with increased capacity.
2Productivity
If lithium cobalt oxide or lithium nickel oxide is used to achieve excellent basic battery characteristics, then capacity and efficiency are improved, but thermal stability and overcharge safety become insufficient
Solution Approach 1:
The cathode active material particles are coated with a safety mechanism layer made of lithium iron phosphate and conductive carbon, creating a composite structure. This composite material approach allows the core to maintain excellent basic battery characteristics while the outer layer provides enhanced thermal stability and overcharge safety, resolving the contradiction between performance and safety.
3Reliability
If spinel-type lithium manganese oxide is used to achieve low cost and high safety, then safety is improved, but electrical capacity becomes too low for high energy density applications
Solution Approach 1:
The cathode structure is segmented into two functional parts: an inner core made of high-capacity lithium cobalt oxide or lithium nickel oxide that provides electrical capacity, and an outer safety mechanism layer made of lithium iron phosphate that provides safety. This segmentation allows each component to fulfill its specific function, achieving both high electrical capacity and high safety.
4Reliability
If olivine-type lithium iron phosphate is used to achieve low cost and high safety, then safety is improved, but electronic conductivity and average operating potential are too low for excellent battery characteristics
Solution Approach 1:
Conductive carbon is introduced as an intermediary component in the safety mechanism layer. The conductive carbon acts as a mediator that enhances the electronic conductivity of the lithium iron phosphate coating, allowing the safety layer to maintain its protective function while improving the overall electrical characteristics of the cathode active material.
Data Source
Figure 1(a)~1(c)
Figure 2(a)~2(d)
Figure 3
AI summary
Disclosed are a cathode active material for lithium seco ndary batteries, a method for preparing the same, and lithium secondary batteries comprising the same. The cathode active material for lithium secondary batteries comprises a lithium metal oxide secondary particle core formed by aggregation of a plurality of lithium metal oxide primary particles; a first shell formed by coating the surface of the secondary particl e core with a plurality of barium titanate particles and a pl urality of metal oxide particles; and a second shell formed b y coating the surface of the first shell with a plurality of olivine-type lithium iron phosphate oxide particles and a plu rality of conductive material particles. The cathode active m aterial for lithium secondary batteries allows manufacture of lithium secondary batteries having excellent thermal stabili ty, high-temperature durability and overcharge safety.