Lithium Metal Phosphate Cathode for Hybrid Vehicle Batteries
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Solution Overview
Problem
Lithium secondary batteries used in hybrid electric vehicles face challenges with high output requirements, poor cycle characteristics, and electrolyte decomposition when using traditional cathode and anode materials, necessitating a solution for enhanced stability and energy density.
Innovation Solution
A lithium secondary battery design incorporating lithium metal phosphate as the cathode active material, amorphous carbon as the anode active material, and an ether-based solvent with ethylene carbonate in the electrolyte, which improves output and cycle life while preventing electrolyte decomposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LiCoO2 is used as cathode active material, then energy density is improved, but output characteristics deteriorate
Solution Approach 1:
The patent changes the chemical composition parameters of the cathode material from conventional LiCoO2 to Li1+aM(PO4-b)Xb, where M represents transition metals (Fe, Mn, Co, Ni, Cu, Zn, Al, Ga, In, Ti, V, Nb, Ta, Zr, Hf) and X represents F, S, or N. This compositional parameter change enables simultaneous achievement of high energy density and superior output characteristics by optimizing the crystal structure and electronic properties of the cathode material.
Solution Approach 2:
The patent employs composite cathode materials combining lithium metal phosphate with transition metal elements and heteroatom substitutions (F, S, N). This composite approach integrates the advantages of different elements to achieve both high energy density from lithium phosphate structure and improved output characteristics from transition metal contributions, resolving the contradiction between energy storage and power delivery.
2Reliability
If LiFePO4 is used as cathode active material, then stability is improved, but electron conductivity deteriorates
Solution Approach 1:
The patent modifies the LiFePO4 structure by introducing transition metal substitutions (M = Fe, Mn, Co, Ni, Cu, Zn, Al, Ga, In, Ti, V, Nb, Ta, Zr, Hf) and heteroatom substitutions (X = F, S, N) in the formula Li1+aM(PO4-b)Xb. These parameter changes optimize the electron conductivity while preserving the stable olivine structure, thereby improving both conductivity and stability simultaneously.
Solution Approach 2:
The patent applies local substitutions of Fe atoms with other transition metals and P atoms with heteroatoms at specific positions in the crystal lattice. This local quality modification enhances electron conductivity in specific regions while maintaining the overall structural stability of the LiFePO4 framework, resolving the contradiction between stability and conductivity.
3Use of energy by moving object
If crystalline graphite is used as anode active material, then energy density is improved, but output characteristics deteriorate
Solution Approach 1:
The patent transitions from crystalline graphite to amorphous carbon as the anode material. This structural parameter change from ordered crystalline to disordered amorphous structure improves output characteristics by facilitating faster lithium ion diffusion pathways, while maintaining high energy density through the carbon's ability to accommodate lithium atoms.
4Temperature
If ether-based solvent is used as electrolyte, then low-temperature performance is improved, but electrolyte decomposition occurs
Solution Approach 1:
The patent introduces Li1+aM(PO4-b)Xb as an intermediary protective layer on the cathode surface that prevents direct contact and decomposition reactions between the ether-based electrolyte and the cathode material. This intermediary layer enables the use of ether-based solvents for improved low-temperature performance while preventing electrolyte decomposition through chemical stabilization.
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 battery exhibits superior high-temperature stability and output characteristics, suitable for hybrid electric vehicles, with reduced internal resistance and extended cycle life, effectively addressing the limitations of existing lithium secondary batteries.
Implementation Method 1
a cathode active material including a lithium metal phosphate according to Formula 1 below... (ii) an anode active material including amorphous carbon... (iii) an electrolyte for lithium secondary batteries including a lithium salt and an ether-based solvent
Implementation Method 2
An electrode potential of the carbon-based active material is 0 V (Li/Li+) during charging of Li ions
Data Source
AI summary
Disclosed is a lithium secondary battery including (i) a cathode active material including a lithium metal phosphate according to Formula 1 below, (ii) an anode active material including amorphous carbon, and (iii) an electrolyte for lithium secondary batteries including a lithium salt and an ether-based solvent,Li1+aM(PO4-b)Xb (1)wherein M is at least one selected from the group consisting of Group II to XII metals, X is at least one selected from F, S, and N, −0.5≦a≦+0.5, and 0≦b≦0.1.