Future Battery Cell Chemistries

Lithium-ion (Li-ion) battery cells and their future chemistries

1. Introduction

Lithium-ion (Li-ion) battery cells are widely used in various industries such as automotive, consumer electronics, and stationary storage, leading to the development of diverse battery cells to meet different needs. This diversity necessitates specific testing requirements and an understanding of each type's unique behavior.

This article discusses the current and expected future variations in Li-ion cells and their testing implications, providing essential knowledge for designing laboratories to test a wide array of current and future Li-ion cells.

2. How do Li-ion battery cells operate?

A 'Li-ion' cell uses lithium ions' intercalation for energy storage and transfer.

When charging, lithium ions move from the cathode to the anode through the electrolyte, and vice versa during discharge, with electrons balancing the charge via an external circuit.

A separator allows ion but not electron transfer, forcing electrons through the external circuit. Current collectors connect the electrodes to this circuit.

For enhanced energy storage, larger cells repeat this component combination, featuring multiple layers over large areas forming a ‘jelly roll’.


Components and lithium/electron transport in a Li-ion battery cell | HORIBA Battery Testing

Figure 1: Illustration of components and lithium/electron transport in a Li-ion battery cell

3. Selecting Li-ion battery cells

Li-ion cells are preferred in many markets for their high energy density, power capability, and longevity. Their design varies to meet the demands of different applications. Common design criteria for energy storage applications include:

  1. Energy Density: Particularly critical for automotive use due to associated range benefits. Both cell and system design, and therefore energy density, depends on electrode chemistries and other components.
  2. Power Density: Essential particularly for hybrid vehicles and fast charging, dependent on cell chemistry and design and often balanced against energy density.
  3. Durability/Lifetime: Varies significantly across cell types both in magnitude and nature. Important to match cell lifespan with application needs e.g. expected temperature range.
  4. Safety: Li-ion cells are generally safe with responsible and correct usage. They can have dangerous failure modes, including thermal runaway to which some chemistries are prone.
  5. Useable Temperature Range: Li-ion cell performance is temperature sensitive. Relative sensitivity and optimum temperature is influenced by cell chemistry and electrode design.
  6. Controllability: Important for battery pack operation. Varies with cell chemistry due to impacts on voltage and resistance profiles.
  7. Cost: Critical for all applications, with cell selection impacting overall system cost.

The importance of these criteria varies by application, with automotive placing a high value on energy density for vehicle efficiency and range.


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4. Li-ion battery cell variations

Chemistry variations in the anode, cathode, and electrolyte, along with unique additives, coatings, and intellectual property, enable manufacturers to enhance electrode and electrolyte performance.

Cell designs, including cylindrical, prismatic, pouch, and button formats, also vary, each offering distinct advantages and drawbacks.

Both chemistry and design are finely adjusted to optimize performance characteristics.

An overview of Li-ion cell variations is shown in Figure 2.

Range of Lithium-Ion battery cell designs and chemistries | HORIBA Battery Testing

Figure 2: Range of Lithium-Ion battery cell designs and chemistries.

Cathode chemistry variations | Battery Cell Chemistry | HORIBA Battery Testing

Figure 3: Cathode chemistry variations.

4.1 Cathode chemistry

The high potential electrode (cathode) significantly influences cell characteristics. Key cathode materials like Nickel-Cobalt-Aluminum (NCA) and Nickel-Cobalt-Manganese (NCM) are preferred in applications valuing energy storage and range. They combine high operating potential with a balance of energy, power, durability, and cost. Lithium-Iron-Phosphate (LFP) cathodes are suitable for fast charging, safety, and longevity. They traditionally have lower energy density but recent advancements are enhancing their competitiveness.

Relative cathode attributes are shown in Figure 3.

The choice of cathode material impacts Li-ion cell behavior in several ways:

  • Operating Voltage. Higher voltage cathodes increase cell voltage.
  • Resistance. Cathode materials differ in resistance, affecting response to current.
  • Degradation. Each cathode chemistry ages uniquely, influenced by material structure, interaction with electrolyte, and mechanical changes during intercalation, impacting ageing rate and symptoms.
  • Safety. All Li-ion cells risk thermal runaway, with the onset temperature, severity and total gas release affected by cathode chemistry.
Anode battery cell chemistry variations

Figure 4: Anode chemistry variations.

4.2 Anode Chemistry

The anode, acting as the low potential component opposite the cathode, typically includes primarily graphite for its low operating potential, high energy density, and affordability. Despite its advantages, graphite facilitates a range  of Li-ion cell ageing mechanisms. Lithium-Titanate-Oxide (LTO) offers an alternative with longer lifespans at the cost of lower cell voltage and energy density due to its higher anode potential.

Silicon is emerging as a promising option or addition to graphite, providing higher energy density. Silicon however faces challenges with volume changes during lithium intercalation, which can lead to rapid degradation if not managed properly.

Relative anode attributes are shown in Figure 4.

The choice of anode material also influences cell behavior:

  • Cell operating voltage. Lower voltage anode materials increase overall cell voltage.
  • Cell resistance. Anode materials differ in energy transfer resistance, influencing current response.
  • Cell degradation. Anode choice greatly impacts cell ageing, often more so than cathode choice. Many ageing mechanisms are directly linked to anode wear and electrolyte interactions.
  • Cell structure requirements. Materials like silicon undergo significant volume changes during lithiation, necessitating specific cell pressure management and breathability adaptations.
  • Cell safety. Anode materials influence the risk of lithium dendrite formation, which can breach the separator and cause thermal runaway. The probability and severity of separator damage varies by material.
4.3 Electrolyte

Electrolytes operate within a specific voltage 'stability range,' requiring compatibility with electrode materials. They significantly affect degradation and safety, influenced by reactions with electrodes and flammability. LiPF6 is widely used in Li-ion cells despite its stability issues and flammability, which can cause thermal runaway by generating excessive heat rapidly. Many manufacturers enhance LiPF6's stability and reduce ageing through proprietary additives.

The choice of electrolyte gives the following considerations:

  • Cell operating temperature range. The electrolyte's temperature sensitivity determines the cell's optimal operating temperature.
  • Cell degradation. Modifying electrolyte properties can significantly affect cell ageing, especially calendar-based ageing.
  • Cell safety. Electrolyte flammability varies, with less flammable options theoretically lowering thermal runaway risks. The electrolyte composition also affects the nature and temperature of gases released during thermal runaway.
  • Mechanical cell requirements. Solid electrolytes necessitate continuous contact with electrodes, presenting challenges like volume changes and cracking, unlike liquid electrolytes. This influences cell pressure and volume management.
  • Electrode choice. Different electrolytes are compatible with specific electrodes, affecting possible electrode combinations.
Illustration of the main cell formats: Cylindrical, prismatic, and pouch

Figure 5: Illustration of the main cell formats: Cylindrical, prismatic, and pouch.*

4.4 Battery Cell Format

Cell materials come in various formats, predominantly cylindrical, prismatic, and pouch (Figure 5*). Button cells are an option typically reserved used for small power applications e.g. hearing aids.

Cell format and size can influence behavior in multiple ways:

  • Degradation. Format affects current distribution and material sensitivity to volume changes. For instance, pouch cells may age faster without proper pressure management due to swelling and gassing.
  • Safety. Certain formats e.g. prismatic can integrate additional safety mechanisms, like pressure relief valves.
  • Thermal management. The format and size determine thermal behavior. Larger cells can generate and accumulate more heat, especially at the center. This requires format and size-specific cooling strategies.
  • Electrical connections. Different terminal connections impact optimal integration into packs/systems.
  • Mechanical requirements. Formats differ in structural integrity; pouch cells, for example, need external support for stability.


*Schröder, R., Glodde, A., Aydemir, M., & Bach, G. (2015). Process to Increase the Output of Z-Folded Separators for the Manufacturing of Lithium-Ion Batteries. Applied Mechanics and Materials, 794, 19–26. https://doi.org/10.4028/www.scientific.net/amm.794.19

5. Future battery cell chemistries

Li-ion technology is advancing with improvements in current technologies, new electrode and electrolyte materials, and innovative approaches beyond lithium intercalation. Key emerging trends include:

  • High Nickel NMC. Increasing nickel content enhances energy density and reduces cobalt dependence. This can increase average cell voltage however it can introduce additional degradation mechanisms, particularly in early life.
  • Silicon Anodes. Silicon gives the possibility of higher energy density than graphite. It does however require careful management of significant volume changes during lithiation.
  • Solid state electrolytes. Replacing liquid electrolytes with solid ones offers advantages like compatibility with more electrode materials for higher energy density and reduced thermal runaway risks due to inflammable electrolytes. Solid electrolytes currently have challenges in managing cell volume and pressure due to their inflexibility and necessitation of maintaining physical contact with electrodes.
  • Lithium Sulfur (Li-S). Utilizes conversion mechanisms instead of intercalation, resulting in lower voltage and unique operational characteristics such as altered OCV and resistance behavior.
  • Sodium-ion. Similar to Li-ion but uses sodium, offering different voltage ranges and operational profiles. Particularly different is a stepwise OCV curve with significant flat regions.

6. Implications on a battery cell laboratory testing

In this section, some of the key differences in Li-ion battery cells will be captured to understand how it could affect aspects of a battery cell laboratory.

Components of a battery cell testing laboratory.

Figure 6: Components of a battery cell testing laboratory.

6.1 Operating temperature range

The operating temperature range of Li-ion cells depends on their chemistry, affecting the choice of thermal chambers and chillers needed to test all cells for a specific application.


Selection of Li-ion battery cell temperature ranges | HORIBA Battery Testing

Figure 7: Selection of Li-ion battery cell temperature ranges.

6.2 Operating voltage range

The operational voltage range of Li-ion cells differs with anode and cathode chemistries, influencing the choice of cell cyclers. It's vital to select a cycler with a suitable voltage range for improved accuracy and resolution while ensuring it can accommodate all potential cell choices for an application.

Selection of Li-ion battery cell voltage ranges | HORIBA Battery Testing

Figure 8: Selection of Li-ion battery cell voltage ranges.

Cell Open-Circuit-Voltages of common Li-ion cell chemistries | HORIBA Battery Testing

Figure 9: Cell Open-Circuit-Voltages of common Li-ion cell chemistries**

6.3 Open circuit voltage

The Open Circuit Voltage (OCV) of a Li-ion cell, influenced by its chemistry, indicates the rest potentials difference between the cathode and anode at a certain State-of-Charge (SoC). OCV typically rises nonlinearly with SoC increase.

This increase varies with chemistry, especially in its rate of change with SoC. LFP cathodes and LTO anodes produce flatter OCV-SoC curves compared to NMC cathodes and graphite anodes. Accurately capturing the curves for these chemistries demands high voltage resolution and precision.

Future technologies like Li-S and Sodium-Ion battery cells, with minimal OCV shifts at certain SoCs, will similarly require precise voltage measurements.

**Comparative Study of Equivalent Circuit Models Performance in Four Common Lithium-Ion Batteries: LFP, NMC, LMO, NCA

6.4    Temperature and pressure control

Li-ion cells vary significantly in formats and size which influences their heat generation and dissipation. All cells produce heat due to resistance to electrical energy transfer, following Ohm's law. Higher resistance and current-capable cells generate more heat. This aspect is crucial for defining thermal chamber capabilities.

For larger or high-current cells active cooling may be required. This is typically done through chillers for fluid circulation and thermal connection during testing. Larger cells' volume-to-surface area ratio can cause internal heat buildup. This poses challenges for effective cooling and temperature estimation. Terminal cooling sometimes offering a more effective cooling method. Cell format also determines the testing fixture for optimal thermal interaction with the cooling system.

Additionally, depending on the cell's format and chemistry, pressure control and external housing might be necessary, especially for pouch cells to prevent swelling and for chemistries like those with solid electrolytes or silicon anodes that demand specific pressures or volume changes. This can guiding test setup design and necessitate pressure measurement.

6.5 Battery cell safety

All Li-ion battery cells can experience thermal runaway, with the likelihood, temperature threshold, peak temperatures, and gas emissions varying by chemistry and design. Larger cells, storing more thermal energy, pose a greater risk and emit more gas during runaway. These considerations are crucial for lab safety and the choice of test chambers, with larger cells necessitating chambers equipped for enhanced safety and better heat and emission management.

'Thermal runaway behavior with chemistry as shown originally in 'Experimental Analysis of Thermal Runaway in 18650 Cylindrical Li-Ion Cells Using an Accelerating Rate Calorimeter, Institute of Applied Materials-Applied Materials Physics, Karlsruhe Institute of Technology

Figure 10: Thermal runaway behavior with chemistry***

***Thermal runaway behavior with chemistry as shown originally in 'Experimental Analysis of Thermal Runaway in 18650 Cylindrical Li-Ion Cells Using an Accelerating Rate Calorimeter', Institute of Applied Materials-Applied Materials Physics, Karlsruhe Institute of Technology

7. How we can help

Designing a lab optimum for the target testing requirements and application while simultaneously versatile enough for the range of possible battery cells is challenging. To design effectively, a large range of data, calculations and consultancy is required.

We have experience in testing, modeling and understanding Li-ion battery cells, as well as extensive experience in lab design. By combining these two areas of expertise, we can assist in developing a lab suitable for your requirements.


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Further Reading

Li-ion cell ageing: Considering Li-Ion Battery Cell Ageing in Automotive Conditions 

EIS for Solid State Batteries: Electrochemical Impedance Spectroscopy for All-Solid-State Batteries: Theory, Methods and Future Outlook

Thermal management: Why Managing Battery Temperature is Vital

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