Hollow Polymer Coated Separator for Lithium-Ion Battery Thermal Stability
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Solution Overview
Problem
Conventional lithium-ion secondary battery separators, such as polyolefin membranes, suffer from high thermal shrinkage, poor electrolyte infiltration, and limited cycle life, leading to safety issues like short circuits and explosions during abuse conditions like overcharge or thermal shock.
Innovation Solution
A microporous membrane separator with a coating of hollow polymer particles and binder particles, where the polymer particles have a shell with nanopores and a cavity, enhancing liquid absorption, ionic conductivity, and reducing heat shrinkage, while the binder particles improve adhesion and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a ceramic layer is coated onto the separator to reduce thermal shrinkage, then thermal stability is improved, but production cost increases and wear on coating and cutting machines increases
Solution Approach 1:
The patent changes the material parameter from ceramic particles to polymer particles with specific glass transition temperatures (95-125°C). This parameter change maintains thermal stability while improving ease of manufacture, as polymer particles cause less wear on equipment and reduce production costs compared to ceramic particles.
Solution Approach 2:
The patent uses polymer particles that are less expensive than ceramic particles, reducing the cost of the coating layer. Although polymer particles may have shorter thermal stability than ceramics, they provide sufficient stability for battery operation while being more cost-effective and easier to process.
2Ease of operation
If a ceramic layer is coated onto the separator to improve infiltration capability, then electrolyte infiltration is improved, but retention performance on electrolyte is limited
Solution Approach 1:
The patent uses polymer particles with porous structures that have both good infiltration capability and retention performance for electrolyte. The porous structure allows electrolyte to penetrate easily while the polymer matrix retains the electrolyte effectively, solving the contradiction between infiltration and retention.
Solution Approach 2:
The patent creates a composite coating layer combining polymer particles with binder, forming a composite material that achieves both good infiltration capability (through porous polymer structure) and retention performance (through the composite matrix structure).
3Ease of manufacture
If conventional polyolefin membranes are used as separators, then manufacturing is simple, but thermal shrinkage increases leading to short circuits
Solution Approach 1:
The patent applies a composite coating layer of polymer particles and binder on the polyolefin membrane. This composite structure maintains the simplicity of manufacturing the base membrane while adding thermal stability through the coating, preventing thermal shrinkage and short circuits.
Solution Approach 2:
The patent changes the thermal properties parameter of the separator by adding a coating layer with specific glass transition temperature (95-125°C), which is higher than the melting point of polyolefin. This parameter change prevents thermal shrinkage while maintaining ease of manufacture of the overall separator structure.
4Quantity of substance
If polyolefin membranes are used as separators, then cost is low, but cycle life is limited due to poor electrolyte absorption
Solution Approach 1:
The patent uses porous polymer particles in the coating layer that have excellent electrolyte absorption capability. This increases the effective quantity of electrolyte retained in the separator, improving ion transport and extending cycle life while maintaining cost-effectiveness.
Solution Approach 2:
The patent changes the surface properties parameter of the separator by adding a polymer particle coating with higher surface tension than polyolefin. This parameter change improves electrolyte absorption capability, extending cycle life without significantly increasing cost.
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 modified separator achieves better room temperature cycle performance, low temperature discharge performance, rate performance, and safety by increasing liquid retention, ionic conductivity, and reducing thermal shrinkage, thereby extending battery life and preventing explosions.
Implementation Method 1
the polymer particle is a hollow shell structure and comprises a shell and a cavity positioned in the shell, an outer surface of the shell is distributed with nanopores which are communicated with the cavity
Implementation Method 2
the ceramic layer may reduce the heat shrinkage of the separator, the ceramic layer can not prevent the temperature of the lithium-ion secondary battery from increasing until the separator is melt
Data Source
AI summary
The present disclosure provides a separator and a lithium-ion secondary battery. The separator comprises: a microporous membrane having micropores; and a coating provided on a surface of the microporous membrane. The coating comprises polymer particles and binder particles. The polymer particle is a hollow shell structure which comprises a shell and a cavity positioned in the shell, an outer surface of the shell is distributed with nanopores which are communicated with the cavity, a particle diameter of the polymer particle is larger than a pore size of the micropore of the microporous membrane; a particle diameter of the binder particle is larger than the pore size of the micropore of the microporous membrane. The lithium-ion secondary battery comprises: a positive electrode plate; a negative electrode plate; the aforementioned separator interposed between the positive electrode plate and the negative electrode plate; and an electrolyte.