Lithium Metal Phosphate Coated Cathode for Thermal Stability
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Solution Overview
Problem
Lithium ion batteries with lithium metal oxide cathodes, such as those composed of nickel, manganese, and cobalt, face challenges in cycle life, safety, and energy capacity retention, especially at high charge/discharge rates, due to thermal instability and inconsistent performance.
Innovation Solution
A method involving a mixture of lithium metal oxide and lithium metal phosphate, where the lithium metal phosphate comprises secondary particles of 0.1 to 3 micrometers in size, from 5 to 100% volume fraction, is used to enhance thermal stability and safety, with specific formulations and processing steps to form a cathode material for improved lithium ion batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If lithium metal oxide cathodes (nickel, manganese, cobalt) are used to achieve high specific charge capacity, then energy capacity is improved, but thermal stability and safety deteriorate
Solution Approach 1:
A lithium phosphate coating is applied as an intermediary layer on the lithium metal oxide cathode particles. This coating layer acts as a protective barrier that improves thermal stability and safety while maintaining the high capacity characteristics of the underlying lithium metal oxide material.
Solution Approach 2:
The cathode is constructed as a composite material system combining lithium metal oxide (for high capacity) with lithium phosphate coating (for thermal stability). This composite structure allows the battery to achieve both high energy capacity and improved safety by leveraging the complementary properties of each material.
2Use of energy by moving object
If lithium metal oxide cathodes are charged to high voltages (4.2V) to increase energy capacity, then energy density is improved, but cycle life and safety deteriorate
Solution Approach 1:
The lithium phosphate coating serves as a protective intermediary that stabilizes the cathode material during high-voltage charging cycles. This coating prevents structural degradation and oxygen evolution that would otherwise occur at 4.2V charging, thereby extending cycle life while maintaining high energy capacity.
Solution Approach 2:
The invention changes the chemical and physical parameters of the cathode surface by applying a lithium phosphate coating. This modification allows the cathode to withstand higher charging voltages (4.2V) without the previous degradation issues, effectively changing the operational parameter window for reliable high-capacity performance.
3Object-affected harmful factors
If conventional coatings and dopants are applied to improve safety, then thermal stability is improved, but cycle life and capacity retention deteriorate
Solution Approach 1:
The invention changes the key parameter of the coating material from conventional options to lithium phosphate specifically. This material choice provides a unique combination of properties: it improves thermal stability and safety while simultaneously maintaining or enhancing cycle life and capacity retention, resolving the trade-off present with other coating materials.
Solution Approach 2:
The lithium phosphate coating is applied specifically to the surface of the lithium metal oxide particles, creating a localized protective layer with optimized properties. This local modification allows the bulk material to maintain its high capacity characteristics while the surface layer provides improved safety and cycle stability.
Data Source
AI summary
Aspects of the invention are based on the discovery that cathode materials and lithium ion batteries comprising the cathode material, having improved thermal stability may be produced from a cathode material that is comprised of a mixture of a lithium metal oxide and a lithium metal phosphate wherein the lithium metal phosphate comprises a volume fraction of secondary particles having a size of 0.1 to 3 μm that is from 5 to 100%, based on the total content of lithium metal phosphate. More specifically cathodes comprising lithium metal phosphates having the recited secondary particle ranges help provide cathode materials that are capable of passing the nail penetration test without generating smoke or flames. Methods of forming the cathode and lithium ion battery comprising the cathode are also provided.