Core-Shell Olivine Particles for Li-Ion Battery Conductivity
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Solution Overview
Problem
Olivine-structured lithium-containing phosphate compounds used in lithium ion secondary batteries face issues with high electric resistance, leading to slow intercalation and release reactions, low discharge capacity at high rates, and metal element elution, which causes capacity drops and internal short circuits, especially under high temperatures.
Innovation Solution
A core-shell structure is implemented for the positive electrode active material particles, where the core particle includes a first olivine-structured lithium-containing phosphate compound with a phosphorous compound, and the shell layer comprises a second olivine-structured lithium-containing phosphate compound, with specific compositions and content ratios to enhance conductivity and suppress metal element elution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating layer is formed on the surface of olivine-structured active material particles to suppress metal element elution, then cycle characteristics are improved, but electric resistance increases and rate characteristics deteriorate
Solution Approach 1:
The invention applies different functional properties to different regions of the active material particle. The core maintains high metal element content for capacity, while the shell layer suppresses elution. This local differentiation resolves the contradiction between suppressing metal element elution (improving cycle characteristics) and maintaining electric conductivity (preserving rate characteristics) by allowing each region to optimize for its specific function without compromising the other.
Solution Approach 2:
The invention creates a composite structure combining the core olivine-structured active material with a shell layer of conductive material. This composite structure allows the core to provide high capacity through metal element content while the shell provides conductivity and elution suppression, thereby resolving the contradiction between cycle characteristics and rate characteristics that cannot be achieved with a single homogeneous material.
2Reliability
If the proportion of coating layer is increased to suppress metal element elution, then cycle characteristics improve, but capacity density decreases
Solution Approach 1:
The invention applies the shell layer in a controlled, partial manner rather than as a thick uniform coating. The shell layer thickness is optimized to provide sufficient elution suppression while minimizing the volume occupied by non-active material. This partial action approach resolves the contradiction between improving cycle characteristics through elution suppression and maintaining capacity density by limiting the proportion of inactive coating material.
3Temperature
If charge and discharge are repeated under high temperatures, then battery performance is tested, but metal element elution increases causing capacity drops and internal short circuits
Solution Approach 1:
The shell layer is applied in advance to the core active material particles before battery operation, creating a protective barrier that prevents metal element elution during high-temperature charge and discharge cycles. This beforehand cushioning resolves the contradiction between achieving high-temperature performance and preventing metal element elution by preparing the protective structure prior to exposure to harsh conditions.
Solution Approach 2:
The shell layer acts as an intermediary between the core active material and the electrolyte, mediating the interaction during high-temperature operation. It allows ionic transport necessary for battery function while blocking metal element elution into the electrolyte. This intermediary function resolves the contradiction between maintaining high-temperature performance and preventing harmful metal element elution.
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
This configuration improves rate characteristics and cycle stability at high temperatures by maintaining conductivity while reducing metal element elution, thereby enhancing the overall performance of lithium ion secondary batteries.
Implementation Method 1
the core particle includes a first olivine-structured lithium-containing phosphate compound including a phosphorous compound
Implementation Method 2
the shell layer comprises a second olivine-structured lithium-containing phosphate compound... suppression of Fe and Mn which originate from the core particle are eluted into a non-aqueous electrolyte
Data Source
AI summary
Positive electrode active material particles for lithium ion secondary batteries include: a core particle including a first olivine-structured, lithium-containing phosphate compound which includes Fe and/or Mn and Li; and a shell layer attached to the surface of the core particle. The shell layer includes a second olivine-structured, lithium-containing phosphate compound which includes Fe and/or Mn and Li. At least the core particle includes a phosphorous compound represented by the formula (1): MemPnOp, where Me is Fe and/or Mn, 0<m≦̸3, 0<n≦̸3, and 0≦̸p≦̸5; a content C1 of the phosphorous compound in the core particle is 0.5 to 3 mol %; and when the shell layer includes the phosphorous compound represented by the formula (1), a content C2 of the phosphorous compound in the shell layer is smaller than the C1.