Conductive Polymer-Coated Cathode Material for Stable Li-Ion Cycling
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Solution Overview
Problem
Lithium transition metal oxides used in lithium secondary batteries face issues with side reactions and structural changes due to electrolyte interaction, leading to reduced stability and conductivity, especially in nickel-based materials, which also suffer from gas generation and capacity loss.
Innovation Solution
A conductive polymer layer, such as a thiophene-based polymer with specific functional groups, is formed on the surface of a lithium nickel-manganese-cobalt oxide core to enhance electrical and ionic conductivity, prevent side reactions, and improve mechanical flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium-containing nickel oxide is used as electrode active material, then discharged capacity and cost are improved, but side reactions with electrolyte occur leading to gas generation and stability deterioration
Solution Approach 1:
A protective layer comprising lithium fluoride and lithium oxynitride is formed on the surface of the lithium-containing nickel oxide particles. This intermediate layer acts as a barrier between the active material and electrolyte, preventing direct contact and side reactions while maintaining ionic conductivity for lithium ion transport, thus resolving the contradiction between high capacity and stability.
Solution Approach 2:
The protective layer is formed as a composite structure containing lithium fluoride and lithium oxynitride in specific ratios (LiF: 1-10 wt%, Li3PO4: 1-10 wt%, carbon: 1-10 wt%). This composite composition provides both chemical stability to prevent side reactions and ionic conductivity to maintain electrochemical performance, addressing the stability-capacity trade-off.
2Reliability
If protective layer is introduced to prevent side reactions, then stability is improved, but ionic conductivity and electrical conductivity are lowered
Solution Approach 1:
The thickness and composition of the protective layer are precisely controlled to optimize the balance between stability and conductivity. By adjusting the content of lithium fluoride (1-10 wt%), lithium oxynitride (1-10 wt%), and carbon (1-10 wt%), the layer provides sufficient protection while maintaining adequate ionic conductivity for practical battery operation.
Solution Approach 2:
The protective layer is applied specifically on the surface of the active material particles rather than throughout the bulk structure. This localized treatment provides protection where it is most needed (at the interface with electrolyte) while leaving the interior active material properties intact, preserving ionic conductivity pathways within the particle structure.
3Duration of action of stationary object
If lithium-containing cobalt oxide is used as electrode active material, then cycle characteristics are improved, but mass use is limited due to low stability and resource limitation
Solution Approach 1:
The invention replaces expensive cobalt-based materials with cheaper nickel-based materials (such as LiNi0.8Co0.1Mn0.1O2 high-nickel materials). The protective layer compensates for the lower inherent stability of nickel-based materials, enabling them to achieve cycle characteristics comparable to or better than cobalt-based materials while being more cost-effective and resource-sustainable.
Solution Approach 2:
The protective layer of lithium fluoride and lithium oxynitride serves as an intermediary that stabilizes the surface of nickel-based materials, preventing degradation during cycling. This allows nickel-based materials to achieve long cycle life and high stability, matching or exceeding cobalt-based material performance without the associated cost and resource issues.
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 results in a lithium secondary battery with improved capacity retention, stability, and high energy density by preventing electrolyte interactions and maintaining conductivity.
Implementation Method 1
a conductive polymer layer present on a surface of the active material core... preventing side reactions between the active material core and an electrolyte
Data Source
AI summary
The present application provides an electrode active material having excellent electrical conductivity and ionic conductivity as well as excellent mechanical flexibility by forming a unique conductive polymer layer on an active material core, while preventing side reactions between the active material core and an electrolyte from occurring, and an electrode comprising the same. Accordingly, it is possible to provide a lithium secondary battery having an excellent capacity retention ratio (lifetime characteristics) according to charging/discharging while having a high energy density. The conductive polymer layer includes a thiophene-based polymer having one or more functional groups selected from the group consisting of a carboxyl group, a hydroxyl group, an amine group, a nitro group, an ether group, a carbonyl group and a flowable functional group.