Core-Shell Cathode Material for Lithium Battery Safety

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Solution Overview

Problem

Lithium secondary batteries face safety issues, particularly with overcharge characteristics, and existing solutions fail to improve safety without compromising basic battery performance or productivity.

Innovation Solution

A cathode active material comprising a lithium metal oxide core coated with an olivine-structured lithium iron phosphate oxide shell, formed through a dry-coating process, which enhances safety by restricting lithium emission during overcharge without reducing unit capacity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If lithium cobalt oxide or lithium nickel oxide is used as cathode active material, then basic battery characteristics are excellent, but safety is insufficient especially overcharge characteristics

Engineering Contradiction:

ImprovesafetyVSAvoidbasic battery characteristics

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent applies composite materials by creating a core-shell structure where lithium metal oxide (high capacity) forms the core and lithium iron phosphate oxide (high safety) forms the shell. This composite structure allows the battery to achieve both excellent basic characteristics from the lithium metal oxide core and improved safety from the lithium iron phosphate oxide shell, resolving the contradiction between safety and basic battery characteristics.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent applies local quality by creating a non-uniform structure where the inner core region has high capacity characteristics (lithium metal oxide) and the outer shell region has high safety characteristics (lithium iron phosphate oxide). This spatial differentiation allows different regions of the cathode active material to fulfill different functions - the core provides capacity while the shell provides safety during overcharge conditions.

Inventive Principle:

Principle #3Local quality

2Quantity of substance

If filling degree of cathode active material is increased to meet high capacity demand, then capacity is improved, but safety apparatuses operate insufficiently resulting in deterioration of safety

Engineering Contradiction:

ImprovecapacityVSAvoidsafety

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent applies preliminary action by pre-forming the lithium iron phosphate oxide shell around the lithium metal oxide core before the battery is assembled and before any overcharge condition occurs. This pre-established protective shell ensures that safety mechanisms are already in place and functional, rather than relying on safety apparatuses that may not operate sufficiently when filling degree is high.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If spinel-structured lithium manganese oxide is used, then low cost and high safety are achieved, but energy density is reduced

Engineering Contradiction:

ImprovesafetyVSAvoidenergy density

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent combines lithium metal oxide (high energy density) as the core with lithium iron phosphate oxide (high safety, low cost) as the shell. This composite structure allows the battery to achieve high energy density from the lithium metal oxide core while simultaneously achieving high safety and low cost characteristics from the lithium iron phosphate oxide shell, resolving the contradiction between safety and energy density.

Inventive Principle:

Principle #40Composite materials

4Reliability

If olivine-structured lithium iron phosphate compound is used, then low cost and high safety are achieved, but electronic conductivity is very low making it difficult to expect excellent battery characteristics

Engineering Contradiction:

ImprovesafetyVSAvoidbattery characteristics

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent creates a composite structure where lithium metal oxide (high electronic conductivity, excellent battery characteristics) forms the core and lithium iron phosphate oxide (low electronic conductivity but high safety) forms the shell. The lithium metal oxide core compensates for the low electronic conductivity of the lithium iron phosphate oxide shell, ensuring excellent overall battery characteristics while maintaining the safety advantages of the lithium iron phosphate oxide.

Inventive Principle:

Principle #40Composite materials

Data Source

PatentUS8927153B2Cathode active material for lithium secondary batteries with core of lithium metal oxide and shell of lithium iron phosphate oxide, method of preparing the same, and lithium secondary batteries comprising the same

Publication Date: 2015.01.06 SEBANG LITHIUM BATTERY CO LTD

AI summary

The present invention relates to a cathode active material for lithium secondary batteries with high safety, a method of preparing the same and lithium secondary batteries comprising the same. The cathode active material of the present invention comprises a lithium metal oxide secondary particle core portion formed by aggregation of lithium metal oxide primary particles; and a shell portion formed by coating the secondary particle core portion with an olivine-structured lithium iron phosphate oxide. The cathode active material of the present invention allows to manufacture lithium secondary batteries with improved safety, especially overcharge characteristics.