High-Nickel Cathode Coating and Additive Strategy for Gas Reduction
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Solution Overview
Problem
Lithium nickel cobalt manganese ternary material-based lithium ion batteries face issues with gas production, cycle life, storage life, and increased direct current resistance due to high nickel content oxidizability, residual lithium, and poor compressive strength, which affect their performance and endurance in electric vehicles.
Innovation Solution
A lithium ion battery design featuring a positive electrode with a matrix coated by discrete and continuous oxide layers, and an electrolyte containing specific additives to form a dense composite film, reducing surface contact and oxidative decomposition, thereby enhancing cycle and storage life and maintaining lithium ion diffusion channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If lithium nickel cobalt manganese ternary material with high nickel content is used to achieve high specific capacity, then the theoretical specific capacity is improved, but the material exhibits strong oxidizability causing electrolyte oxidation reaction and structural change
Solution Approach 1:
A coating layer comprising Li2SiO3 and Li4SiO4 is formed on the surface of the lithium nickel cobalt manganese ternary material particles. This coating layer acts as an intermediary barrier between the high-nickel material and the electrolyte, preventing direct contact and thus eliminating the oxidation reaction while maintaining the high specific capacity of the underlying material.
Solution Approach 2:
A thin film coating layer with specific composition (Li2SiO3 and Li4SiO4) is applied on the particle surfaces. This thin film provides protective functionality by isolating the reactive high-nickel material from the electrolyte, preventing structural changes and maintaining electrochemical stability without significantly increasing particle size.
2Loss of substance
If excess lithium salt is added to compensate for lithium loss during sintering, then the lithium loss is compensated, but residual lithium remains on the surface forming Li2O that absorbs CO2 and H2O to form LiOH and Li2CO3
Solution Approach 1:
The residual lithium on the particle surfaces, which would normally react with CO2 and H2O to form harmful Li2CO3 and LiOH, is instead converted into beneficial Li2SiO3 and Li4SiO4 through reaction with silicon-containing compounds. This transforms the harmful residual lithium into a protective coating component that prevents further harmful reactions.
Solution Approach 2:
The chemical composition of the surface layer is changed by introducing silicon elements that react with residual lithium to form Li2SiO3 and Li4SiO4. This parameter change in surface chemistry eliminates the formation of harmful Li2CO3 and LiOH, thereby reducing gas production while maintaining lithium content.
3Shape
If lithium nickel cobalt manganese ternary material is present as secondary particles formed by agglomeration of primary particles, then the material structure is formed, but the compressive strength is poor and specific surface area increases after crushing
Solution Approach 1:
Primary particles are agglomerated to form secondary particles with a core-shell structure where the primary particles are embedded in a matrix. The coating layer is continuously distributed across the particle surfaces, merging the individual primary particles into a unified secondary particle structure that resists crushing and maintains low specific surface area.
Solution Approach 2:
The secondary particles are formed as composite structures combining multiple primary particles with a coating layer matrix. This composite architecture provides enhanced mechanical strength and structural integrity, preventing particle breakdown during electrode manufacturing while maintaining the desired morphology.
4Ease of manufacture
If the specific surface area is significantly increased after positive electrode active material is crushed, then the material is processed, but the contact area with electrolyte increases intensifying gas production
Solution Approach 1:
The coating layer of Li2SiO3 and Li4SiO4 serves as a permanent intermediary barrier that remains intact even after particle crushing. This protective layer prevents direct contact between the electrolyte and the high-nickel material surfaces, eliminating oxidation reactions and gas production regardless of the increased surface area from particle size reduction.
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 effectively reduces gas production, prolongs cycle and storage life, and inhibits the increase in direct current resistance, improving the power performance and stability of lithium ion batteries.
Implementation Method 1
the electrolyte is likely to result in an electrochemical oxidation reaction on a surface of the positive electrode
Implementation Method 2
an additive A and an additive B... can facilitate the formation of a dense and strong composite film on the surface of the positive electrode
Implementation Method 3
can effectively maintain an unimpeded diffusion channel of lithium ions during cycling and storage
Data Source
AI summary
The present disclosure provides a lithium ion battery including a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. The positive electrode plate includes a positive electrode current collector, and a positive electrode film disposed on a surface of the positive electrode current collector and containing a positive electrode active material. The positive electrode active material includes a matrix, a first coating layer on the matrix in form of discrete islands, and a second coating layer on the first coating layer and the matrix as a continuous layer. The electrolyte includes an additive A and an additive B. The additive A is selected from a group consisting of cyclic sulfate compounds represented by Formula 1 and Formula 2, and combinations thereof, and the additive B is one or two selected from lithium difluorobisoxalate phosphate and lithium tetrafluorooxalate phosphate.