NCM Positive Electrode Coating for High-Voltage Stability
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Solution Overview
Problem
Lithium nickel cobalt manganese oxide (NCM) positive electrode active materials used in lithium secondary batteries face performance deterioration at high voltages due to increased side reactions with the electrolyte, leading to instability and reduced durability during charging and discharging.
Innovation Solution
A positive electrode active material formed by agglomerating polycrystalline primary particles of lithium composite metal oxide with specific chemical composition and size, doped or surface-coated with elements like Al, Ti, Mg, Zr, Y, and B, to minimize the interface with the electrolyte, enhancing high-voltage performance and volume change durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If NCM is used as a positive electrode active material at a high voltage of 4.35 V or more, then the energy density and voltage are improved, but side reaction with the electrolyte is increased leading to performance deterioration
Solution Approach 1:
A coating layer comprising at least one of a metal oxide, metal hydroxide, metal carbonate, or metal oxyhydroxide is formed on the surface of the NCM positive electrode active material. This coating layer acts as an intermediary barrier between the NCM material and the electrolyte, preventing direct contact and reducing side reactions while allowing the battery to operate at high voltages of 4.35V or more, thus maintaining both high energy density and reliable performance
Solution Approach 2:
The patent modifies the surface properties of the NCM material by changing the chemical composition parameters through doping with elements such as Al, Ti, Mg, Zr, Y, Sr, or B in controlled amounts (0.01-0.5 mol ratio based on total metal elements). This parameter change stabilizes the crystal structure and reduces surface reactivity, enabling the material to maintain stability at high operating voltages while preserving its high energy density characteristics
2Reliability
If the interface between the positive electrode active material and the electrolyte is minimized, then the side reaction is reduced, but the contact area for electrochemical reactions is decreased
Solution Approach 1:
The patent applies a coating layer with specific local properties on the surface of the NCM particles. The coating layer has different characteristics from the bulk material - it provides chemical stability and low reactivity with the electrolyte at the surface interface, while the underlying NCM material maintains its high electrochemical activity. This local differentiation allows the material to resist side reactions at the interface while preserving efficient electrochemical reactions
Solution Approach 2:
The positive electrode active material is designed as a composite structure consisting of the core NCM material (providing high capacity and voltage) and a surface coating layer (providing stability and protection). This composite structure combines the advantages of both materials - the NCM core delivers high energy density while the coating layer reduces side reactions, thus resolving the contradiction between interface minimization and reaction efficiency
3Ease of manufacture
If lithium nickel cobalt manganese oxide is used to replace lithium cobalt oxide, then the cost is reduced, but the stability at high state of charge is deteriorated
Solution Approach 1:
The coating layer serves as a protective intermediary that stabilizes the NCM material at high states of charge. By preventing direct interaction between the NCM and electrolyte, the coating layer suppresses decomposition and structural degradation that would otherwise occur at high SOC, thereby achieving cost-effective NCM material with improved stability comparable to or exceeding traditional LCO
Solution Approach 2:
The patent modifies the compositional parameters of NCM by incorporating additional metal elements (Al, Ti, Mg, Zr, Y, Sr, B) in optimized ratios. These compositional changes enhance the structural stability and electrochemical performance of the material, allowing it to maintain stability at high SOC conditions while benefiting from the lower cost of NCM compared to LCO
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 solution improves high-voltage performance and durability by reducing side reactions and maintaining contact between primary particles, resulting in increased energy density and extended lifespan of lithium secondary batteries.
Implementation Method 1
the primary particle is doped or surface-coated with at least one element M selected from the group consisting of Al, Ti, Mg, Zr, Y, Sr, and B
Implementation Method 2
the primary particle is doped or surface-coated with at least one element M selected from the group consisting of Al, Ti, Mg, Zr, Y, Sr, and B
Implementation Method 3
a secondary particle formed by agglomerating a plurality of polycrystalline primary particles
Data Source
AI summary
A positive electrode active material for a lithium secondary battery is provided having a secondary particle formed by agglomerating a plurality of polycrystalline primary particles including a lithium composite metal oxide of Chemical Formula 1, wherein an average crystallite size of the primary particle is 180 to 400 nm, a particle size D50 of the primary particle is 1.5 to 3μm, and the primary particle is doped or surface-coated with at least one element M selected from the group consisting Al, Ti, Mg, Zr, Y, Sr, and B in an amount of 3,800 to 7,000 ppm:Lia(NixMnyCozAw)O2+b [Chemical Formula 1].