Lithium Secondary Battery Cathode Material Optimization

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Solution Overview

Problem

Lithium secondary batteries used in hybrid electric vehicles face challenges with high output, long cycle life, and stability due to limitations in existing cathode and anode materials, such as LiCoO2 and LiFePO4, which exhibit poor output characteristics and increased internal resistance.

Innovation Solution

A lithium secondary battery utilizing lithium metal phosphate with an olivine crystal structure, specifically LiFePO4, as the cathode active material and amorphous carbon as the anode active material, with a conductive carbon coating to enhance electrical conductivity, and specific particle size and surface area ranges to optimize ionic and electrical conductivity.

Engineering Contradictions & Design Principles

VSEngineering 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

Engineering Contradiction:

Improveenergy densityVSAvoidoutput characteristics

Core Design Contradiction:

Use of energy by moving objectVSPower

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 is a transition metal and X is F, S, or N. This parameter change in chemical stoichiometry and crystal structure enables simultaneous achievement of high energy density and superior output characteristics by optimizing electron conductivity while maintaining high capacity.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite cathode materials combining lithium metal phosphate with transition metals (M = Mn, Fe, Co, Ni, Cu, Zn, Ga, In, Sr, Ti, V, Nb, Mo, Rh, Ir, Pt) and anions (X = F, S, N). This composite approach integrates the high capacity of olivine structure with enhanced electron conductivity from transition metal doping, resolving the contradiction between energy density and output characteristics.

Inventive Principle:

Principle #40Composite materials

2Reliability

If LiFePO4 is used as cathode active material, then stability is improved, but electron conductivity deteriorates

Engineering Contradiction:

ImprovestabilityVSAvoidelectron conductivity

Core Design Contradiction:

ReliabilityVSPower

Solution Approach 1:

The patent modifies the LiFePO4 structure by introducing transition metal substitutions (M) at specific sites and anion substitutions (X = F, S, N) at the phosphate group, creating Li1+aM(PO4-b)Xb. This parameter change in chemical composition increases electron conductivity by introducing charge carriers and modifying the electronic band structure, while the olivine framework maintains structural stability.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies local quality modification by substituting transition metals at specific crystallographic sites within the olivine structure. The transition metal substitution occurs at controlled ratios (0 < x ≤ 0.5 in Li1+aFe1-xMx(PO4-b)Xb), creating localized regions of enhanced conductivity without compromising the overall structural integrity and stability of the cathode material.

Inventive Principle:

Principle #3Local quality

3Use of energy by moving object

If crystalline graphite is used as anode active material, then energy density is improved, but output characteristics deteriorate

Engineering Contradiction:

Improveenergy densityVSAvoidoutput characteristics

Core Design Contradiction:

Use of energy by moving objectVSPower

Solution Approach 1:

The patent changes the anode material from crystalline graphite to amorphous carbon, representing a fundamental parameter change in structural order. Amorphous carbon provides superior output characteristics due to its disordered structure that facilitates faster Li-ion diffusion pathways, while maintaining sufficiently high energy density for HEV applications.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent inverts the conventional choice by selecting amorphous carbon instead of crystalline graphite. This inversion of the structural order parameter (from crystalline to amorphous) reverses the typical trade-off, achieving both high energy density and superior output characteristics simultaneously, making the battery suitable for HEV power-train applications requiring high power delivery.

Inventive Principle:

Principle #13The other way round (Inversion)

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 achieves low resistance and superior output characteristics, making it suitable for hybrid electric vehicles by improving high-temperature stability and rate performance.

Implementation Method 1

with a conductive carbon coating to enhance electrical conductivity

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 2

lithium secondary battery including (i) a cathode active material including a lithium metal phosphate

Methodology Applied

Scientific EffectElectrochemical reaction: Redox Reactions

Data Source

PatentUS9853288B2Lithium secondary battery

Publication Date: 2017.12.26 LG ENERGY SOLUTION LTD

AI summary

Disclosed is a lithium secondary battery including (i) a cathode active material including a lithium metal phosphate according to Formula 1 below; and (ii) an anode active material including amorphous carbon,Li1+aM(PO4−b)Xb (1)wherein M is at least one selected from metals of Groups II to XII, X is at least one selected from F, S and N, −0.5≦a≦+0.5, and 0≦b≦0.1.