Core-Shell LiMn2O4 for High Voltage and Cycle Stability

Solution Overview

Problem

5 V-level positive electrode active materials for lithium ion secondary batteries face issues with capacity drop and crystal structure deterioration at high temperatures, and struggle to achieve theoretical discharge capacity.

Innovation Solution

A lithium manganese composite oxide with the formula Li a (M x Mn 2-x-y Y y )(O 4-w Z w), where M includes Fe and optionally Ni or Cu, Y is selected from Li, Be, B, Na, Mg, Al, K, Ca, Ti, and Si, and Z is F or Cl, optimized to maintain high operating voltage and capacity while reducing Mn 3+ instability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If Mn is substituted with Fe to achieve 5 V-level operating potential, then energy density is improved, but capacity drop with cycles and crystal structure deterioration at high temperature occur

Engineering Contradiction:

Improveenergy densityVSAvoidcycle stability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent applies local quality by creating a core-shell structure where the inner core region contains Fe-substituted LiMn2O4 for high voltage operation, while the outer shell region contains Al-substituted LiMn2O4 for structural stability. This spatial differentiation of composition allows simultaneous achievement of high energy density and cycle stability.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent creates a composite material system combining two different substituted spinel structures (Fe-substituted and Al-substituted LiMn2O4) in a core-shell configuration. The composite structure leverages the high voltage characteristics of Fe-substitution while utilizing the structural stability of Al-substitution to prevent capacity fade.

Inventive Principle:

Principle #40Composite materials

2Power

If Mn is substituted with Fe to increase operating potential, then discharge capacity increases, but discharge capacity value cannot be theoretically obtained

Engineering Contradiction:

Improvedischarge capacityVSAvoiddischarge capacity achievement

Core Design Contradiction:

PowerVSManufacturing precision

Solution Approach 1:

The patent optimizes the substitution ratios of Fe and Al, as well as the sintering temperature and atmosphere parameters, to achieve the theoretical discharge capacity. By precisely controlling these parameters, the material realizes near-theoretical capacity while maintaining structural integrity.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If LiMn2O4 is used as positive electrode active material, then cost is reduced and high temperature stability is improved, but capacity drop occurs at high temperature

Engineering Contradiction:

ImprovecostVSAvoidhigh temperature performance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies local quality by creating a core-shell structure where the inner core region contains Fe-substituted LiMn2O4 for high voltage operation, while the outer shell region contains Al-substituted LiMn2O4 for structural stability. This spatial differentiation of composition allows simultaneous achievement of high energy density and cycle stability.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent optimizes the substitution ratios of Fe and Al, as well as the sintering temperature and atmosphere parameters, to achieve the theoretical discharge capacity. By precisely controlling these parameters, the material realizes near-theoretical capacity while maintaining structural integrity.

Inventive Principle:

Principle #35Parameter changes

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 composition enhances cycle stability and energy density by reducing Mn 3+ instability and valence changes, achieving a high operating voltage and capacity retention.

Implementation Method 1

By substituting Mn with Fe, Mn is present in a quadrivalent state, discharge is caused by the reaction of Fe 3+/Fe 2+, Mn 4+/Mn 3+

Methodology Applied

Scientific EffectRedox reactions: Redox Reactions

Data Source

PatentEP3327836B1Positive electrode active material for secondary battery and secondary battery using the same

Publication Date: 2018.12.12 NEC ENERGY DEVICES LTD

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AI summary

Provided is a lithium ion positive electrode active material for a secondary battery that can realize a high operating voltage and a high capacity while suppressing capacity drop with cycles by using a low-cost material. A positive electrode active material for a secondary battery, which is a lithium manganese composite oxide represented by the following general formula (I) Lia(MxMn2-x-yYy)(O4-wZw) (I) wherein in the formula (I), 0.5 ≤ x ≤ 1.2, 0 < y ≤ 0.3, 0 ≤ a ≤ 1.2, and 0 < w ≤ 1; M contains at least Fe and may further contain at least one selected from the group consisting of Ni, Cr and Cu other than Fe; Y is at least one selected from the group consisting of Li, Be, B, Na, Mg, Al, K, Ca, Ti and Si; and Z is at least one of F and Cl.