The Role of Battery Design and Architecture

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Battery Module and Pack Design Considerations

Battery design and architecture plays a critical role in battery performance and lifespan. Batteries are made of two electrodes made of materials capable of redox reactions that are separated by an electronically insulating but ion conducting electrolyte. Spontaneous chemical reactions at the electrodes drive the movement of electrons through the external circuit and the migration of ions through the electrolyte. The efficiency and feasibility of these charge–discharge processes are governed by material properties at the nanoscale, as well as the structural and engineering design of the cell and battery at the macroscale.

Active vs Inactive Components

The energy stored in a battery is dependent on active electrode materials intrinsic properties including capacity, redox potential and density. The cathode and anode active materials are redox active and trigger ion movement during the charging/discharging cycles. However, a battery is also made up of other components to safely harness energy for a given application. The mass of battery packaging, the separator, electrolyte, current collector and conductive additives must be balanced against the electrochemically active materials in battery design.

The theoretical capacity of the active electrode materials is dependent on chemical composition and structure, as well as the valence state of the redox centers. The atomic mass of the material influences specific capacity, where lighter materials are preferred. The practical capacity of the active materials is influences not only by the material and its intrinsic properties but also the environment in which it exists. The electrode architecture, interface conditions and battery use conditions are also influencing factors.

Battery Material Design Considerations

Electrode Materials

Anode Materials

An ideal anode must have low electrode potential, extremely high specific capacity and high conductivity. This must also be balanced with battery stability and lifespan. While lithium metal is the ideal anode material for lithium-ion batteries due to its high specific capacity with no requirements for host material, dendritic growth of lithium during charging has serious safety concerns.

Typical high energy anodes comprise 5 wt% silicon oxide or silicon nanoparticles with the majority material being graphite. The high theoretical capacity of silicon enhances the practical capacity of pure graphite. Silicon is currently not seen as a viable stand-alone anode material due to its excessive volume expansion upon ion intercalation. It also has low chemical stability towards common electrolytes.

Cathode Materials

High energy cathode materials are highly desirable to improve battery performance. Cathode active materials must have high stability in their delithiated state as well as electrode-electrolyte stability. The stability of the delithiated crystal structure can be improved, for example, by doping with other elements, such as aluminum. This is the case for the ternary cathode material NCA which has a specific capacity of ~ 190 mAh/g. Nickel-rich cathode materials have demosntrated increased energy density. The capacity is enhanced due to the higher oxidation states of nickel (Ni^2+/3+ to Ni⁴⁺⁾ during charging. Cathode materials can also be modified with surface coating to enhance their electrochemical properties.

Cathode Active Materials

Cathode Active Materials

Explore the range of high-purity cathode materials designed for high-capacity, high-voltage batteries to maximize energy density.

Anode Active Materials

Anode Active Materials

Explore the range of anode active materials including graphite for high lithium storage and excellent conductivity.

Electrolyte

The electrolyte stability window is an important consideration when considering battery safety. The open-circuit voltage should typically lie within the electrolyte stability window to avoid excessive break down of electrolyte. However, the practical electrolyte stability winder may be larger than the thermodynamic value. The degradation of electrolyte can be hindered through the formation of a passivation layer referred to as the solid electrolyte interphase (SEI). This passivation layer is dependent on multiple battery components. The electrode material and electrolyte both influence the formation of the SEI.

The HOMO-LUMO gap of the electrolyte is a key property that influences the electrolyte stability window, but it is not the only factor. The surface chemistry of the electrode materials including coatings or passivation layers also influence the stability window.

Solid electrolytes (SEs) offer a promising solution to the decomposition issues associated with liquid electrolytes. They are generally more resistant to lithium dendrite formation, reducing the risk of thermal runaway. However, solid electrolytes face two key challenges: low ionic conductivity and poor interfacial contact with electrode materials, which can limit overall battery performance.

Electrode Design Considerations

The active electrode material provides the electrochemical reactivity needed for energy storage, however to ensure efficient electronic conductivity other components must be considered. Adding conductive additives can increase the efficiency of electron movement. A conductive network can form preventing localized overcharging, which in turn can improve battery lifespan and safety. The current collector also plays a role in harnessing electrons and proving a conductive connection to the external circuit.

At the electrode design stage we must maximise the selected active materials intrinsic materials based on the desired application of the battery. Here we must consider both the crystal structure of materials as well as the macrostructure of the electrode. The packing and connectivity here influences the effectiveness of the material properties to influence battery performance. Below are some considerations that must be taken when designing electrodes for batteries.

Material Composition and Capability

• Blending of active materials: Incorporate complementary active materials (e.g. LMO into NMC or NCA cathodes) to enhance performance characteristics.
• Use of conductive additives and binders: Tailor formulations to improve electronic conductivity, mechanical integrity, and electrochemical stability.
• Particle integrity: Ensure particles maintain their structure during processing to prevent degradation or capacity loss.
• Particle and pore size distribution: Optimize for uniformity to promote consistent ionic transport and electrode performance.
• Current collector thickness: Optimize to manage thermal and ohmic resistance, directly affecting both energy and power density of the cell.

Structural and Physical Properties

• Porosity, tortuosity, and permeability: Design the electrode microstructure to balance ionic/electronic transport with mechanical stability.
• Electrode thickness: Adjust to influence energy density (through active/inactive material ratio) and power density (via internal resistance).
• Electrode shape and geometry: Optimize for uniform current distribution and mechanical compatibility with cell design.
• Drying behavior: Prevent drying-related defects such as cracking or delamination during solvent removal.

Moisture and Contamination Control

• Water content control: Keep water levels in the electrode mix to low ppm levels to avoid degradation of moisture-sensitive materials.
• Current collector surface condition: Monitor and control current collector foil moisture levels and oxidation to preserve interface quality and prevent delamination.
• Contamination prevention: Implement safeguards to avoid the introduction of impurities that could compromise electrode integrity.

The application of the battery ultimately influences the components that you have selected and the structure of your electrodes. Typically, batteries fall into high-power or high-energy batteries, each requiring different design strategies:

Battery Cell Design Considerations

With the electrodes architecture selected, the next stage in battery design is putting the cell together. Here we must consider the electrolyte and separator components. There allow our electrodes to be ionically connected without short-circuiting electronically. The cell itself comes in different formats depending on the requirements of the larger battery.

Electrolyte and Separator System

• Electrolyte type and properties: Select electrolytes (liquid, gel, or solid-state) based on conductivity, voltage stability, operating temperature range, and chemical compatibility.
• Electrolyte filling and wetting: Ensure uniform and complete wetting of internal components to prevent dry spots and enhance ionic transport. Solid electrolyte (SE) can provide a solution to the excessive SEI formation seen with some liquid electrolyte. However, SE faces challenges of poor ionic conductivity at room temperature and low compatibility with some high-voltage cathode active materials and metallic lithium.
• Separator design: Choose separators with adequate mechanical strength, thermal stability, and appropriate porosity to ensure safe and consistent ionic flow.

Cell Architecture and Format

• Cell format selection: Choose between cylindrical, prismatic, or pouch cells based on application requirements such as volume efficiency, mechanical robustness, and thermal behavior:
  • Cylindrical cells: Possess high energy densities due to the good use of volume via the winding of electrodes. The cell is highly robust and cheap to manufacture due to established techniques.
  • Prismatic cells: Due to their high mechanical robustness, they can be integrated directly into modules and packs. They offer lower energy densities due to the weight of the cell housing and lower ratio of active material.
  • Pouch cells: Provide high energy density due the flexibility in manufacturing and low cell housing weight. Another benefit is that battery recycling may be easier when it is no longer useful.
• Stacking or winding method: Determine whether cells use stacked layers, jelly rolls, or Z-fold configurations to balance energy density, manufacturability, and structural stability.
• Tab and terminal layout: Design efficient current pathways through optimized tab placement, tab welding, and terminal geometry to minimize internal resistance and heat generation. Tabless designs make use of the direct connection of uncoated segments of the current collector foils with the cell contacts. By this technique, the contact area between the current collector and cell contacts can be drastically increased and thermal and electrical conductivity improved.

Thermal Management and Safety

• Heat dissipation: Design for efficient heat removal through cell geometry, tab layout, and external interfaces to avoid thermal hotspots during operation.
• Built-in safety mechanisms: Integrate features like PTCs, CID vents, pressure relief devices, and flame-retardant additives to address overpressure and over-temperature risks.

Mechanical and Structural Integrity

• Swelling and pressure tolerance: Account for internal pressure build up and dimensional changes over cycling, especially in pouch and prismatic formats.
• Sealing and enclosure: Ensure long-term integrity through robust sealing methods (e.g. heat sealing, laser welding) and materials that resist corrosion and electrolyte permeation.
• Dimensional consistency: Maintain tight tolerances in cell thickness and form factor for seamless module integration.

Battery Module and Pack Design Considerations

In conventional battery pack design, a cell is a component within a battery module which is a component within a battery pack. Modules are groups of cells assembled together with added structure, wiring and safety features. Packs are made up of multiple modules and include the electronics, cooling and protection needed for the battery to be used in a device, car or grid.

In recent battery technology, battery cells are designed to be placed directly in battery packs without the need for modules. This is often referred to as cell-to-pack technology, or C2P / CTP for short. By removing the module inactive components the battery energy density dramatically increases at the pack level. Such battery packs are thought to see a 20-30% increase in volume utilization, 40% reduction in number of parts, and 50% increase in production efficiency.

Battery design at the module and pack level is primarily engineering focused:

• The electrical configuration must balance series (voltage) vs parallel (current/capacity) connections in order maintain safe and even operation across all the cells.
• The battery management system monitors and controls charging-discharging.
• Cooling systems within both modules and packs offer thermal management.
• Frames, casing and supports hold the cells in place and protect against physical damage.
• Connectors, communication protocols, and mounting points vary depending on the application.

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