1.Role and Selection Criteria of Anode Materials
1.1.Principles for Selecting Anode Materials for Lithium-ion Batteries
Selection Principles for Anode Materials：
High specific energy;
As low as possible electrode potential relative to lithium electrode;
Good reversibility during charging and discharging processes;
Favorable surface structure that forms a good SEI film with the electrolyte;
Excellent structural dimensions and mechanical stability during insertion/extraction processes to ensure good cycling performance;
Good electronic and ionic conductivity of the insertion compound to reduce polarization;
High diffusion coefficient of lithium ions within the material for facile rapid charging and discharging;
Abundant resources and low cost;Stable and non-toxic in air.
2.Types of Anode Materials
Classification of Anode Materials for Lithium-ion Batteries:
Currently, the commercialized anode materials are mainly graphite, LTO, and silicon-based materials.
2.1.Development Direction
Silicon anodes and lithium metal anodes have become the medium- to long-term development directions due to their high specific capacity.
3.Introduction to Anode Materials
3.1.Graphite
1.Graphite is a commonly used anode material in lithium-ion batteries.
Graphite mainly includes:
Natural Graphite
Artificial Graphite
2.What is Graphite?
①Graphite has a layered structure, with the layers bound together by van der Waals forces.
②The basal plane and edge plane of graphite exhibit different properties.
4.Commonly Used Modification Schemes for Graphite Anodes
4.1.Graphite Material Charging and Discharging
During the insertion of lithium into graphite, the charging and discharging voltage remains relatively stable. The reversible insertion of lithium ions into the graphite layers primarily occurs below 0.2V. There are distinct lithium insertion platforms near the three potential levels of 0.2V, 0.12V, and 0.08V.
4.2.Compatibility of Graphite with Electrolytes
The choice of electrolyte has a significant impact on the electrochemical performance of the material!
4.3.Soft Carbon and Hard Carbon
1.Soft carbon, also known as easily graphitized carbon, is amorphous carbon that can be graphitized at temperatures above 2500°C. Soft carbon has a low degree of crystallization (or graphitization), small grain size, and a large interplanar spacing (d002). It exhibits good compatibility with electrolytes. However, it has a high irreversible capacity during the initial charge-discharge cycle, a relatively low output voltage, and no distinct charge-discharge platform potential. Common examples of soft carbon include petroleum coke, needle coke, carbon fibers, and carbon microspheres.
2.Hard carbon refers to carbon that is difficult to graphitize. It is the pyrolysis carbon of high-molecular-weight polymers, and this type of carbon remains difficult to graphitize even at temperatures above 2500°C. Common examples of hard carbon include resin carbon (such as phenolic resin, epoxy resin, and polyfurfuryl alcohol PFA-C).
4.4.Comparison of Different Carbon Material Structures
4.5.Titanium Oxides(Li4Ti5O12)
Spinel Structure
Poor Conductivity (~10-13 S/cm)
High Potential (vs.Li)
Typically Prepared by Solid-Phase Method
Advantages:
Excellent structural stability of the crystal during lithium ion insertion/extraction; zero strain
Outstanding cycling performance and discharge voltage platform
High potential (1.56V), avoiding electrolyte decomposition and formation of interfacial protective films
Abundant raw material sources (TiO2, Li2CO3, LiOH, or other lithium salts)
4.6.The main disadvantages of LTO are its high voltage platform, low specific capacity, and high cost, which limit its applications.
4.7.Alloy-based Materials
Silicon-Carbon Battery = 50% Silicon-Carbon Material (Nano-Silicon + Composite Technology) + 50% Supporting Facilities
4.8.Silicon Anode
1.Although alloys have high capacity, they also experience significant volume expansion (up to 300%). Nanostructuring is necessary to mitigate this expansion.
2.Currently commercialized silicon anodes are primarily silicon oxide and silicon/carbon composite materials.
4.9.Material Modification for High Energy Density
Purpose:1. Increase the graphitization degree of the material and enhance its energy density.
Purpose:2.Reduce surface defects, lower reactive sites, and minimize electrolyte consumption, thereby ensuring high initial efficiency and cycling performance of the battery.
4.10.Material Modification - Low Rebound
4.11.Material Modification - Balanced Type
4.12.Material Modification -Fast Charging
Interface Design - Coating with Amorphous Carbon
Idea: Coating with amorphous carbon can significantly reduce the electrochemical reaction impedance of the material, enhancing its power performance and performance at low temperatures.
4.13.Material Modification - Fast Charging
Idea: Using small-particle graphite to shorten the lithium ion diffusion distance, increase electrolyte wetting area, and reduce the OI value of the electrode, effectively enhancing the material's rate capability and fast charging performance.
5.Canrd Brief Introduce
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6.
Q & A
During this Q&A session, Dr. Ke addressed each of the questions raised by the audience, providing detailed answers.
BlackBlack: "Can reducing the negative electrode's voltage increase the voltage and thus enhance the battery's energy density?"
Dr. Ke:
"The potential of the material is mainly determined by its structure. There are some ways to improve it, but the changes are generally limited."
Jingxin: "What are some representative products of soft and hard carbon, and what are their applications?"
Dr. Ke:
"Currently, soft carbon has very limited applications. Hard carbon was used in some fast-charging battery systems in the past—companies like Sumitomo and Kureha had products in this area. However, with the improvement of graphite coating technologies, graphite can now achieve fast-charging effects with higher energy density, so hard carbon applications are now quite limited."
BlackBlack: "Why choose a low-voltage negative electrode?"
Dr. Ke:
"A low-voltage negative electrode is chosen to match the positive electrode. The full-cell voltage is the potential of the positive electrode minus the potential of the negative electrode. The greater the difference, the higher the voltage."
Yanhuoゝ: "What are the differences in charging and discharging protocols between pure silicon monoxide and regular graphite?"
Dr. Ke:
"The lithium insertion potential can be set similarly for both. However, the lithium extraction voltage depends on the application of the full cell. Since silicon monoxide has a higher potential, a higher charging voltage is needed to fully extract lithium, whereas the graphite negative electrode doesn't require this—its capacity is almost fully released at around 0.8V."
Lee: "What methods are generally used to improve the compatibility of artificial graphite with PC?"
Dr. Ke:
"Artificial graphite naturally has fewer defects compared to natural graphite, making it much better in this regard. Additionally, surface coatings on some graphite can effectively improve compatibility."
缘来是妳: "The structure of silicon oxide seems to be a topic of debate. What is the mechanism of lithium storage in silicon oxide?"
Dr. Ke:
"Analyzing silicon oxide microscopically, it's mainly composed of silicon dioxide and nano-silicon. During the initial lithiation reaction, silicon dioxide reacts with lithium to form lithium silicate, which has poor reversibility, while nano-silicon forms a reversible lithium-silicon alloy. Although some earlier reports suggested the reaction with silicon dioxide was irreversible, recent studies have found it to be partially reversible, though it still consumes a significant amount of lithium."
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