Composite Positive Electrode Sheet for Fast-Charging Cycle Stability
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Solution Overview
Problem
Existing positive electrode materials, particularly rich nickel layered transition metal oxides and lithium manganese iron phosphate, face issues with rate performance, structural stability, and safety, which hinder their application in power batteries, especially due to rapid material failure and high internal resistance during charging and discharging cycles.
Innovation Solution
A composite positive electrode sheet is designed with a layered structure material close to the current collector for improved electron transfer and a microporous olivine structure layer for enhanced lithium-ion migration, using specific conductive agents and pore forming agents to balance conductivity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If lithium iron phosphate materials are mixed with ternary positive electrode materials, then energy density is improved, but current distribution becomes unbalanced leading to rapid material failure
Solution Approach 1:
The positive electrode is divided into two separate layers: a first layer containing lithium iron phosphate material and a second layer containing ternary positive electrode material. This segmentation prevents the current distribution problems associated with mixing while maintaining the energy density benefits of the ternary material.
Solution Approach 2:
Different regions of the positive electrode are assigned different material compositions and functions. The first layer (closer to current collector) uses lithium iron phosphate for stability, while the second layer (farther from current collector) uses ternary material for high energy density, creating optimal local properties in each region.
2Reliability
If ternary positive electrode materials are used, then conductivity is improved, but current concentration leads to rapid failure during charging and discharging cycles
Solution Approach 1:
The electrode is segmented into two layers with the ternary material confined to the second layer. This prevents current concentration issues while preserving the conductivity advantages of ternary materials in the region where they are applied.
Solution Approach 2:
The first layer containing lithium iron phosphate material acts as an intermediary between the current collector and the second layer containing ternary material. This intermediary layer distributes current more evenly, preventing the current concentration that leads to rapid failure in pure ternary electrodes.
3Reliability
If lithium manganese iron phosphate material is used, then safety and stability are improved, but constant current is low limiting fast-charging performance
Solution Approach 1:
The electrode structure provides different local qualities: the first layer with lithium manganese iron phosphate offers safety and stability near the current collector, while the second layer with ternary material provides high conductivity and fast-charging capability at the outer region, achieving both safety and productivity.
Solution Approach 2:
The positive electrode uses a composite structure combining two different positive electrode materials (lithium iron phosphate or lithium manganese iron phosphate in the first layer, and ternary material in the second layer) to achieve synergistic effects that overcome the limitations of either material alone.
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 composite structure enhances peeling force, cycle stability, and fast-charging performance, reducing rapid material failure and internal resistance, thereby extending the battery's service life and ensuring safety.
Implementation Method 1
facilitate the transfer of electrons from a current collector to a positive electrode active material layer
Implementation Method 2
increase the migration rate of lithium-ions
Data Source
AI summary
A positive electrode sheet, a method for preparing the same, and its application. The positive electrode sheet includes a positive electrode current collector and a composite positive electrode active material layer arranged on at least one side surface of the positive electrode current collector; the composite positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer stacked in sequence, the second positive electrode active material layer is arranged on a side, away from the positive electrode current collector, of the first positive electrode active material layer; a material of the first positive electrode active material layer comprises a positive electrode material with a layered structure, and a first conductive agent; and a material of the second positive electrode active material layer comprises a positive electrode material with an olivine structure, a second conductive agent, and a pore forming agent.