• EV Batteries
• Battery Basics
• Cell Chemistry & Parts
• Cell formats
• Battery Pack & Configuration
• Battery Management System
• Thermal Management
• Cell Balancing
• Charging
• Degradation
• Buffer
• Manufacturers
• Warranty

Cell chemistry & parts

Battery cells are the most important part of the battery system and the most critical factor for both cost and performance in EVs.

Anode

The anode is one of the two electrodes in an electric vehicle (EV) battery, the other being the cathode. During the discharge cycle, oxidation occurs at the anode, releasing electrons into the external circuit to power the device or vehicle. During the charging cycle, reduction occurs at the anode, absorbing electrons from the external circuit and storing energy in the battery.

In a lithium-ion battery, the anode is typically made of graphite, which has a layered structure that allows lithium ions to intercalate between the layers. When the battery discharges, lithium ions move from the anode to the cathode through the electrolyte, while electrons flow through the external circuit. During charging, the reverse process occurs, with lithium ions moving from the cathode back to the anode.

The performance of the anode is crucial for the overall performance and safety of an EV battery. A high-quality anode material should have high lithium-ion storage capacity, good conductivity, structural stability, and resistance to degradation over multiple charge and discharge cycles. While graphite anodes meet these requirements, researchers are exploring other materials like silicon, which has a much higher storage capacity but is more prone to degradation.

Companies like StoreDot are working on silicon-based anodes. This could theoretically double cell-level energy density, benefiting EVs significantly. Silicon anodes could also improve the appeal of lower energy cells, such as LFP, narrowing the gap to NMC-based cells and minimizing LFP’s core disadvantage—limited energy density. Estimates show that incorporating 20% silicon into an anode could improve an LFP cell’s energy density by 17%, although the additional cost may be prohibitive.

Cathode

The cathode is the electrode where reduction occurs during the discharge cycle, accepting electrons from the external circuit to power the device or vehicle. During the charging cycle, oxidation occurs at the cathode, releasing electrons into the external circuit and storing energy in the battery.

In a lithium-ion battery, the cathode is typically made of a metal oxide, such as lithium cobalt oxide (LCO), lithium nickel cobalt manganese oxide (NMC), or lithium iron phosphate (LFP). The choice of cathode material significantly impacts the performance, safety, and cost of the battery.

Lithium Nickel Manganese Cobalt Oxides (NMC)

NMC cathodes are popular for EV batteries due to their high energy density and good thermal stability. They offer a balance between energy density and power density, making them suitable for a wide range of EV applications.

Different versions of NMC cathodes, such as NMC111, NMC532, and NMC622, refer to the ratios of nickel, manganese, and cobalt. Higher nickel content increases energy density but also cost. Recent developments include NMC811 and NMC622, which offer even higher energy density but may have challenges related to thermal stability and cycle life. NCM9 is the latest evolution, with 90% nickel content.

The particle size and morphology of the cathode material also impact performance. Smaller particles can improve rate capability and power density, while larger particles may enhance energy density.

Lithium Nickel Cobalt Aluminum Oxides (NCA)

NCA cathodes have high energy density and are used in EV batteries, particularly in Tesla’s vehicles. They offer high energy density and good performance, making them a popular choice for many EV manufacturers.

NCA cathodes typically include nickel, cobalt, aluminum, and oxygen. They offer high energy density, resulting in a longer driving range for EVs. NCA cathodes also have good power density and long cycle life but can be sensitive to high temperatures, requiring sophisticated thermal management systems.

Lithium Iron Phosphate (LFP)

LFP is a cathode material commonly used in EV batteries due to its high thermal stability and long cycle life. LFP cathodes have lower energy density compared to other types but offer good safety, durability, and cost-effectiveness.

LFP cathodes consist of lithium iron phosphate (LiFePO4), a stable and non-toxic material. They are popular in China due to strict safety regulations. Brands like Tesla use LFP in their lower-range models.

Advantages of LFP

• High thermal stability, reducing the risk of thermal runaway.
• Long cycle life, making them suitable for applications requiring high reliability.
• Lower cost compared to nickel-based chemistries.

Disadvantages of LFP

• Lower energy density, making them less suitable for high driving range EVs.
• Poor performance in cold weather, affecting discharge capacity and charging speed.

Lithium Manganese Iron Phosphate (LMFP)

LMFP combines the high safety of LFP and the high energy density of lithium manganese phosphate (LMP). It is a promising cathode material for high-performance lithium-ion batteries, especially for EVs.

Advantages of LMFP

• High thermal stability and low risk of thermal runaway.
• High power density and fast charging capability.
• Long cycle life and good rate performance.
• Low cost and environmental friendliness.
• High voltage platform and improved specific capacity.

Challenges of LMFP

• Low electronic conductivity and lithium-ion diffusion coefficient.
• Phase transition and lattice distortion during cycling.
• Manganese dissolution at high temperatures.
• Electrolyte compatibility and interface stability.

Summary of Cathode Materials

Separator

A separator is an essential component of an EV battery, placed between the cathode and anode to prevent short circuits. It is typically a thin, porous membrane made of polymer material that allows lithium ions to flow between the electrodes while preventing electron flow.

The separator provides a physical barrier, allows lithium-ion flow, and helps maintain the battery’s internal structure by preventing dendrite formation. A good separator material should have high ion conductivity, low electrical conductivity, and good thermal stability.

Common separator materials include polyethylene (PE), polypropylene (PP), and ceramic materials like lithium aluminum titanium phosphate (LATP).

Electrolyte

Liquid electrolytes in lithium-ion batteries consist of lithium salts in an organic solvent, such as ethylene carbonate, dimethyl carbonate, and diethyl carbonate. They act as a conductive pathway for cations moving between electrodes during discharge and charging.

Solid-state batteries, which use solid electrolytes, offer potential advantages like higher energy density, faster charging, longer lifespan, and better safety. However, they face challenges like high cost, low power density, and poor interface stability.

Semi-solid and quasi-solid state batteries are hybrid types combining solid and liquid electrolytes, aiming to overcome some drawbacks of solid-state batteries.

Current Collector

The current collector facilitates the flow of electrical current between the electrode and the external circuit. In lithium-ion batteries, it is typically a thin metal foil made of copper or aluminum, coated with carbon to improve conductivity and prevent corrosion.

The design and materials of the current collector significantly impact the battery cell’s performance and durability.

EV Battery Explained with Food

In the video below, Battery Scientist & Engineer Jill Pestana from the YouTube channel Across the Nanoverse explains the different battery parts using food.