Li-ion Cathode Over-discharge Protection via Voltage Plateau
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Solution Overview
Problem
Lithium-ion batteries face cell failure and degradation due to over-discharge, particularly at elevated temperatures, as the increased potential at the negative electrode can cause copper current collector dissolution, which existing methods like adding Li2NiO2 or LiFePO4 do not adequately prevent.
Innovation Solution
A cathode material with a voltage plateau below the copper dissolution potential, composed of xLi2MnO3.(1−x)LiMnaNibCocO2, is used to provide over-discharge protection by incorporating an electrochemically active material, binder, and electrically conducting components, ensuring a predetermined irreversible capacity loss and voltage step below 2V vs. Li, thereby preventing copper dissolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Li2NiO2 or LiFePO4 is added to the cathode as over-discharge protection, then the cathode can provide some protection against over-discharge, but the redox potentials (3.6-3.7V for Li2NiO2 and 3.45V for LiFePO4) are higher than the copper dissolution potential (3.3V), so copper dissolution still occurs at zero voltage particularly at elevated temperatures
Solution Approach 1:
The patent changes the voltage parameter of the cathode material by using Li2MnO3 which has a redox potential of approximately 4.0V, and through composite formulation achieves a voltage plateau below 3.3V vs Li during discharge. This parameter change ensures the cathode potential remains below the copper dissolution threshold even at zero cell voltage and elevated temperatures, effectively preventing copper dissolution while providing over-discharge protection.
Solution Approach 2:
The patent uses a composite cathode material formulation combining Li2MnO3 with other lithium metal oxides or hydroxides (such as LiCoO3, LiNi0.8Co0.1Mn0.1O2, LiMn2O4, LiFePO4) in specific ratios. This composite approach leverages the high voltage plateau of Li2MnO3 to establish thermodynamic protection while the overall composite delivers a voltage plateau below the copper dissolution potential, achieving both over-discharge protection and prevention of copper dissolution.
2Object-affected harmful factors
If a cathode material with voltage plateau below copper dissolution potential is used, then copper dissolution is prevented, but the cathode must exhibit irreversible capacity loss during first charge to ensure proper potential matching with the anode
Solution Approach 1:
The patent carefully controls the voltage parameter of the cathode material to achieve a voltage plateau between 2.5V and 3.3V vs Li during discharge. This specific voltage range ensures the cathode potential remains below the copper dissolution threshold (3.3V) while the irreversible capacity loss during first charge (typically 5-15%) is optimized to match the anode's irreversible loss, achieving proper potential matching without excessive energy loss.
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 cathode material effectively mitigates over-discharge damage by maintaining the anode potential below the copper dissolution threshold, ensuring the battery's integrity and performance, even at elevated temperatures.
Implementation Method 1
the cathode is a combination of one or more of (i) an electrochemically active materials, (ii) a binder, and (iii) an electrically conducting material
Implementation Method 2
the increase in potential at the negative electrode (anode) can cause cell failure or degradation by oxidizing and dissolving the current collector material
Data Source
AI summary
A lithium-ion battery having over-discharge protection includes an anode comprising at least an electrochemically active anode material, said anode having an anode irreversible capacity loss during a first charge of the lithium-ion battery; and a cathode comprising at least an electrochemically active cathode material characterized by the formula:xLi2MnO3.(1−x)LiMnaNibCocO2,where 0<x<1 and a+b+c=1, and x, a, b, and c are selected to provide a cathode irreversible capacity loss during a first charge of the lithium-ion battery that is greater than or equal to the anode irreversible capacity loss, and wherein the cathode possesses a voltage step less than about 2 V versus Li.