Graphene batteries, while promising, face several challenges related to their material properties and electrochemical performance. These challenges include dendrite growth, cathode oxygen release, anode phase transformation, crystal expansion, and interfacial delamination.
Dendrite Growth
Dendrite growth is a major issue in graphene batteries, as it can lead to short-circuits and safety concerns. Dendrites are needle-like structures that can form on the anode surface during charging, penetrating the separator and causing internal short-circuits. This can result in thermal runaway, fire, and even explosion.
- Dendrite growth is influenced by factors such as electrolyte composition, current density, and temperature.
- Typical dendrite growth rates can range from 0.1 to 10 μm/h, depending on the operating conditions.
- Dendrite formation can reduce the Coulombic efficiency of the battery, leading to capacity fade over cycling.
Cathode Oxygen Release
Cathode oxygen release is another challenge in graphene batteries, as it can result in capacity fade and poor cycle life. During charging and discharging, the cathode material can undergo structural changes that lead to the release of oxygen, which can react with the electrolyte and cause degradation.
- Oxygen release is particularly problematic in high-energy-density cathode materials, such as nickel-rich NMC (nickel-manganese-cobalt) oxides.
- Typical oxygen release rates can range from 0.1 to 1 wt% per cycle, depending on the cathode material and operating conditions.
- Oxygen release can also lead to the formation of gas bubbles, which can cause mechanical deformation and delamination of the electrode.
Anode Phase Transformation
Anode phase transformation is a challenge in graphene batteries, as it can contribute to capacity fade and poor cycle life. During cycling, the anode material can undergo structural changes, such as the conversion between different lithium-ion storage phases, which can lead to volume changes and mechanical degradation.
- Typical volume changes during lithiation/delithiation can range from 10% to 300%, depending on the anode material.
- Phase transformations can also lead to the formation of new crystalline phases, which can have different electrochemical properties and contribute to capacity fade.
- Anode phase transformations are particularly problematic in silicon-based anodes, which can undergo large volume changes during cycling.
Crystal Expansion
Crystal expansion is another challenge in graphene batteries, as it can lead to capacity fade and reduced rate capability. During cycling, the insertion and extraction of lithium-ions can cause the crystal structure of the electrode materials to expand and contract, leading to mechanical stress and degradation.
- Typical volume changes during lithiation/delithiation can range from 10% to 300%, depending on the electrode material.
- Crystal expansion can lead to the formation of cracks and fractures in the electrode, which can reduce the active surface area and impede ion transport.
- Crystal expansion is particularly problematic in high-energy-density electrode materials, such as silicon-based anodes and nickel-rich NMC cathodes.
Interfacial Delamination
Interfacial delamination is a challenge in graphene batteries, as it can lead to loss of electrical contact and further degrade battery performance. During cycling, the repeated expansion and contraction of the electrode materials can cause the interfaces between the electrode, current collector, and other battery components to delaminate, leading to increased resistance and capacity fade.
- Interfacial delamination is influenced by factors such as the mechanical properties of the materials, the quality of the interfaces, and the operating conditions.
- Typical delamination rates can range from 0.1% to 1% per cycle, depending on the battery design and operating conditions.
- Interfacial delamination can also lead to the formation of cracks and fractures in the electrode, which can further exacerbate the problem.
To address these challenges, researchers are exploring various in situ TEM techniques to better understand the nanoscale electrochemistry of batteries and correlate structural changes with electrical output at various states of charge and discharge. These techniques involve carrying out real battery tests such as galvanostatic discharge, cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy inside TEM.
Recent reports have shown the possibility of measuring pA-level current flowing through a single nanowire-based battery, observing small-scale solid electrolyte interphase (SEI) evolution and lithium (de)plating in microfluidic TEM cells for galvanostatic and cyclic voltammetry studies.
However, translating nanoscale findings to bulk-level battery electrochemistry requires considering the impact of material interfaces and size effects on mass transfer and transport. Future work should thus incorporate more details about the effect of cell dimension, geometrical electrode configurations, and microfluidic conditions on the accuracy of electrochemistry quantification.
In terms of graphene-specific battery challenges, one key issue is the restacking of graphene sheets, which can lead to a decrease in the surface area available for charge storage and transport. This can be mitigated by incorporating spacers or functional groups between the graphene sheets to prevent restacking and maintain a high surface area.
Another challenge is the integration of graphene with other battery components, such as the electrolyte and current collectors. This requires careful optimization of the interfaces between these components to ensure efficient charge transfer and minimize interfacial resistance.
In terms of technical specifications, graphene batteries can offer high energy and power densities, long cycle life, and fast charge/discharge capabilities. For instance, a graphene-infused material developed by researchers at the Pacific Northwest National Laboratory, Princeton University, and Vorbeck Materials has shown potential for improving the power and cycling stability of lithium-ion batteries, while maintaining high energy storage.
This material involves the use of lithium metal with thin films made of Vorbeck’s patented graphene material, or composite materials containing the graphene materials, to create 3D nanostructures for battery electrodes. The resulting battery material has the potential to store large amounts of energy and recharge quickly, with energy densities up to 500 Wh/kg and power densities up to 10 kW/kg.
However, the specific performance metrics can vary depending on the battery design and composition, and further research is needed to address the challenges outlined in this playbook.
References:
– Understanding materials challenges for rechargeable ion batteries: in situ TEM of rechargeable batteries, Nature Communications, 2017, 8, 15806.
– Graphene-based Lithium Ion Battery Market Geographical Growth, LinkedIn, 2024-04-02.
– The emergence of graphene research topics through interactions, Journal of the Serbian Chemical Society, 2022-06-22.
– Solving Challenges in Energy Storage, U.S. Department of Energy, July 2019.
– The challenge and opportunity of battery lifetime prediction from field data, ScienceDirect, 2021-08-18.
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