Lithium-Ion Positive Electrode Thermal Stability via Resistivity Control
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Solution Overview
Problem
Lithium metallic oxides used in lithium-ion secondary batteries have low thermal stability, and mixing with olivine-type phosphate compounds does not consistently enhance thermal stability due to varying qualities and conditions.
Innovation Solution
A positive electrode comprising a lithium metallic oxide with a lamellar rock-salt structure and a phosphate/carbon composite, where the olivine-type phosphate compound is coated with carbon, and the volume resistivity ratio of the phosphate/carbon composite to the lithium metallic oxide is maintained at 0.034 or less, ensuring excellent thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium metallic oxide is mixed with olivine-type phosphate compound to enhance thermal stability, then thermal stability is improved, but the consistency of thermal stability enhancement varies due to different qualities and conditions of the materials
Solution Approach 1:
The invention changes the critical parameter from simple mass ratio mixing to volume resistivity ratio control (specifically, maintaining the volume resistivity ratio of phosphate/carbon composite to lithium metallic oxide at 0.034 or less). This parameter change ensures consistent thermal stability enhancement regardless of variations in material qualities, as volume resistivity is a fundamental electrical property that can be precisely controlled and measured.
Solution Approach 2:
The invention uses a phosphate/carbon composite material where carbon is coated on the olivine-type phosphate compound. This composite structure provides both the thermal stability of the phosphate compound and the electrical conductivity of carbon, creating a material with optimized properties that consistently enhances battery thermal stability when mixed with lithium metallic oxide in the appropriate volume resistivity ratio.
2Reliability
If carbon is coated on olivine-type phosphate compound to create phosphate/carbon composite, then electrical conductivity is improved, but the volume resistivity ratio must be precisely controlled to maintain thermal stability benefits
Solution Approach 1:
The invention identifies volume resistivity ratio as the critical control parameter, setting it at 0.034 or less. This single parameter controls both the electrical conductivity (through carbon coating) and thermal stability (through the phosphate compound), simplifying the control process despite the composite material structure.
Solution Approach 2:
The carbon coating acts as an intermediary that bridges the electrical conductivity needs and thermal stability requirements. By controlling the carbon coating amount and quality, the volume resistivity is adjusted to the optimal range, which in turn ensures consistent thermal stability enhancement without requiring complex multi-parameter control.
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 provides a positive electrode with enhanced thermal stability, preventing excessive current flow to the lithium metallic oxide and thereby suppressing thermal decomposition, leading to improved battery performance.
Implementation Method 1
a rate of a volume resistivity of the phosphate/carbon composite with respect to a volume resistivity of the lithium metallic oxide being 0.034 or less
Data Source
AI summary
A positive electrode for lithium-ion secondary battery includes: a lithium metallic oxide with a lamellar rock-salt structure including nickel, cobalt, and manganese; and a phosphate/carbon composite including an olivine-type phosphate compound at least some of which is coated with carbon partially. A rate of a volume resistivity of the phosphate/carbon composite to a volume resistivity of the lithium metallic oxide is 0.034 or less. The olivine-type phosphate compound is expressed by a general formula: LiMhPO4 (where “M” is at least one element selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, Te and Mo, and 0<“h”<2). A content of the phosphate/carbon composite is from 15% by mass or more to 35% by mass or less when a summed mass of the lithium metallic oxide and the phosphate/carbon composite is taken as 100% by mass.