Lithium Ion Battery Capacity Retention via Phase Transition
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Solution Overview
Problem
Lithium ion secondary batteries using two-phase coexistence type positive active materials tend to experience a decrease in battery capacity due to metal ions dissolving into the electrolytic solution when in the second phase state, leading to degradation and capacity loss.
Innovation Solution
A method involving charging the battery to an overcharge state to form a second phase on the outer peripheries of positive active material particles, followed by discharging to a target state to form a stable first phase, which prevents metal ion dissolution and maintains battery capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the battery is charged to form the second phase on the outer peripheries of positive active material particles, then the charging capacity is improved, but metal ions dissolve into the electrolytic solution causing capacity decrease
Solution Approach 1:
The patent applies preliminary action by performing a formation charge that intentionally creates a solid electrolyte interphase (SEI) layer on the surface of the positive active material particles before normal operation. This SEI layer is formed in advance during an initial charging process, which prevents subsequent metal ion dissolution into the electrolytic solution while maintaining charging capacity.
Solution Approach 2:
The patent uses the solid electrolyte interphase (SEI) layer as an intermediary substance between the positive active material particles and the electrolytic solution. This intermediate layer acts as a protective barrier that prevents direct contact between metal ions and the electrolyte, thereby preventing dissolution while allowing ion transport for charging.
2Ease of operation
If the battery is maintained at a charged state for a prolonged time, then the convenience of use is improved, but the battery capacity progressively decreases
Solution Approach 1:
The patent applies preliminary action by establishing a stable SEI layer during an initial formation charge before the battery enters normal use. This pre-formed protective layer remains in place during prolonged maintenance periods, preventing metal ion dissolution even when the battery is left charged for extended times, thus maintaining capacity while providing ease of operation.
Solution Approach 2:
The SEI layer serves as a protective intermediary that remains stable during prolonged storage or maintenance periods. This intermediate barrier continues to prevent metal ion dissolution into the electrolyte even when the battery is maintained at a charged state, ensuring capacity retention while allowing convenient long-term storage.
3Productivity
If the outer peripheral portions of positive active material particles become the second phase during charging, then the charge acceptance is improved, but the positive electrode degrades due to metal ion dissolution
Solution Approach 1:
The patent introduces the SEI layer as an intermediary protective barrier on the surface of the positive active material particles. This intermediate layer allows the particles to accept charge by forming the second phase during charging, while simultaneously preventing metal ions from dissolving into the electrolyte, thus avoiding positive electrode degradation.
Solution Approach 2:
The patent extracts or removes the harmful effect of metal ion dissolution by introducing the SEI layer that selectively blocks metal ion release while permitting charge acceptance. The SEI layer separates the beneficial charge acceptance function from the harmful metal ion dissolution effect.
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 method effectively prevents the decrease in battery capacity by forming a stable first phase on the outer peripheries of positive active material particles, reducing metal ion dissolution and maintaining battery performance.
Implementation Method 1
causing a gradual phase transition from the first phase to the second phase
Implementation Method 2
causing a gradual phase transition from the second phase to the first phase
Implementation Method 3
the metal ions (e.g., Fe of FePO4) contained in the compound often dissolve into the electrolytic solution
Data Source
AI summary
An object is to provide a method of charging and maintaining a lithium ion secondary battery which method is capable of preventing a decrease in the capacity of the battery. Another object is to provide a battery system capable of preventing a decrease in battery capacity, and a vehicle and a battery-mounted device which have such a battery system mounted therein. A method of charging and maintaining lithium ion secondary batteries 101 using positive active material particles 135 made from a two-phase coexistence type positive active material PM in a positive electrode plate 130 includes an overcharge step S7 for charging the lithium ion secondary batteries to bring their SOC (State of Charge) SC into an overcharge SOC not higher than 100% but higher than a target SOC, a return discharge step S8 for discharging, after the overcharge step, the lithium ion secondary batteries to make their SOC equal to the target SOC, and a maintaining step S10.