Lithium Battery Overcharge Detection via Olivine Cathode Potential Shift
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Solution Overview
Problem
Lithium secondary batteries face challenges in detecting an overcharged state quickly to prevent safety valve activation, which can lead to increased internal pressure and potential safety issues due to the use of electroconductive polymers increasing production costs and complexity.
Innovation Solution
A lithium secondary battery design incorporating a cathode with a phosphate compound of olivine structure, an anode, a separator, an electrolyte with a supporting salt concentration of 0.5 to 1 mol/L, and a safety valve with a valve-opening pressure of 25 kgf/cm2 to 30 kgf/cm2, allowing rapid potential increase upon overcharging to detect the overcharged state before safety valve activation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electroconductive polymer is used to detect overcharged state, then detection capability is improved, but production cost and manufacturing complexity increase
Solution Approach 1:
The invention extracts the detection function from separate electroconductive polymer layers and integrates it directly into the cathode active material itself. By selecting cathode materials with inherent potential characteristics that indicate overcharge states, the patent eliminates the need for additional detection layers, thereby reducing manufacturing steps and production cost while maintaining detection capability.
Solution Approach 2:
The cathode active material serves multiple functions: it acts as both the energy storage component and the overcharge detection element. The potential increase during overcharge is inherently exhibited by the cathode material itself, making it a multi-functional component that eliminates the need for separate detection systems.
2Reliability
If safety valve opening pressure is set low, then safety response is improved, but battery performance and energy density are reduced
Solution Approach 1:
The invention implements preliminary detection of overcharge states by monitoring potential increase in the cathode material before the safety valve is triggered. This early detection allows the system to identify problematic conditions while maintaining normal operating pressure ranges, thereby preserving battery energy density while ensuring safety through timely detection and 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 battery effectively terminates charging before safety valve activation, enhancing safety by quickly increasing potential when overcharged, thus preventing excessive internal pressure and ensuring a highly safe lithium secondary battery operation.
Implementation Method 1
a cathode having a phosphate compound of olivine structure as a cathode active material... the battery, when overcharged, can rapidly increase its potential
Implementation Method 2
an electrolyte comprising a supporting salt dissolved therein... an initial amount of Li contained in the electrolyte is within the range of 5 to 20
Data Source
AI summary
A main object of the present invention is to provide a lithium secondary battery whose potential can be rapidly increased immediately after the start of overcharge, thereby terminating charging before a safety valve is actuated. This object can be solved by a lithium secondary battery comprising: a cathode having a phosphate compound of olivine structure as a cathode active material, an anode, a separator sandwiched between the cathode and the anode, an electrolyte comprising a supporting salt dissolved therein, and a safety valve having a valve-opening pressure within the range of 25 kgf/cm2 to 30 kgf/cm2, wherein assuming that the initial amount of Li contained in the cathode is 100, the initial amount of Li contained in the electrolyte is within the range of 5 to 20.