Battery Market Segmentation 

The battery market is categorically divided into consumer, automotive, industrial, and special applications, which include aerospace and military sectors. 

In consumer electronics, lithium-ion batteries have become the major rechargeable power sources due to their high energy density, lightweight nature, and long cycle life. This chemistry is favored for its ability to deliver sustained and reliable performance in devices such as smartphones, laptops, cameras, and portable electronic gadgets. Automotive applications traditionally use batteries for Starting, Lighting, and Ignition (SLI), with lead–acid being the exclusive chemistry employed. Newer automotive systems, such as Hybrid Electric Vehicles (HEV), Plug-in Hybrid Electric Vehicles (PHEV), and Electric Vehicles (EV), employ other battery chemistries. The industrial sector further classifies batteries for mobile and stationary applications. This segmentation underscores the varied and evolving requirements across sectors within the battery industry.

Considering their wide range of applications, electrochemical cells and batteries can also be classified according to their shapes, sizes, and designs. Ensuring optimal, safe, and reliable battery pack design involves a crucial technological step: proper cell containment and packaging.¹

Cell components

An electrochemical cell, or simply cell, is the basic electrochemical unit of batteries. In these cells, the conversion of chemical to electrical energy through the reduction and oxidation of electrochemically active materials occurs. 

Cells are composed of these four major components: (1) positive and (2) negative electrodes, (3) electrolyte, and (4) separator.²

Electrodes

Battery cells have positive (cathode) and negative (anode) electrodes. During the discharging of secondary battery cells, electrons from an external circuit go to the cathode, where they drive the reduction of the electrochemically active material. On the anode, oxidation occurs, producing the needed electrons for the reduction reaction on the cathode. Both electrodes are composed of two primary components: an active material and a substrate or current collector. 

The active material is the component that undergoes reversible chemical reactions during the electrochemical processes of discharging (energy release) and charging (energy storage). In the context of cathode and anode materials in rechargeable batteries, the active material plays a crucial role in the movement of ions and electrons between the electrodes, contributing to the overall energy storage and release capabilities of the battery. 

• Cathode active materials (CAM) are commonly metal oxides. However, its specific composition depends on the target electrochemical properties and requirements of the battery chemistry in use. For example, for the commercially dominant lithium-ion batteries, the most common CAMs are lithium cobalt oxide (LiCoO₂), lithium manganese oxide (LiMn₂O₄), lithium iron phosphate (LiFePO₄ or LFP), and lithium nickel manganese cobalt oxide (LiNiMnCoO₂ or NMC). Similarly, in other battery chemistries like sodium-ion, nickel-metal hydride (NiMH), or lithium-sulfur batteries, different cathode materials are employed. The choice of cathode material is influenced by factors such as energy density, voltage characteristics, cost, and safety considerations.³
• On the other side, anode active materials (AAM) are mainly carbon-based, with graphite being the most widely used due to its high conductivity, affordability, and stable structure. Silicon anodes, while providing higher energy density, face challenges related to volume expansion and shorter cycle life. Some approaches involve 'doping' graphite anodes with a small amount of silicon to enhance performance and energy density.

The active materials are coated onto substrates or current collectors using a slurry, composed of the active material, polymeric binder, and carbon additive. The polymeric binder and carbon additive enhances the adhesion of the active material to the substrate and increases the conductivity of the coating, respectively. Current collectors provide mechanical support to the active materials. In addition, they also provide conductive paths at which the electrons can travel towards the external circuitry.⁴ Current collectors are equally important cell components as controlling their properties yield significant performance improvements. Reducing their thickness and increasing strength allows the stacking of more active materials in confined spaces, increasing the volumetric energy density of the battery. Meanwhile, improving the adhesion between the active material and CC establishes additional electron pathways, decreasing the internal resistance within the cell. The most commonly used anode and cathode current collectors are Cu and Al foils, respectively. In lithium-ion batteries, Cu foil is stable under the anodic potential (0–1.5 V vs. Li/Li⁺), whereas Al foil works well under the cathodic potential (3–4.7 V vs. Li/Li⁺). Interchanging the current collector is not possible because Cu foil undergoes dissolution at potentials > 3.5 V (vs. Li/Li⁺), and Al makes an alloy with Li at 0.26 V (vs. Li/Lⁱ⁺). 

Electrolyte

The electrolyte in a battery facilitates the movement of charged ions between the cathode and anode, enabling the charging and discharging processes. It usually comes in liquid or paste form. The electrolyte's primary function remains consistent across various battery types. It serves as the medium for transporting charged ions, a crucial function in the overall operation of the battery.

Separator

In battery design, a separator, acting as an electrical insulator, prevents direct contact between positive and negative electrodes while facilitating the transfer of ions (ionic conductivity). The electrodes, separator, and electrolyte are assembled within a case or container, with terminals providing electrical connections to the external circuit. For safety, cells may include features like valves or current interrupt devices. Manufacturers have introduced various separator materials, with notable progress occurring in the second half of the 20th century in the chemical industry. Battery separators are categorized based on physical and chemical characteristics, composition, and structure, resulting in types such as nonwoven, microporous, ion-exchange, and nanoporous separators.⁵

Components of Primary Battery Cells

Components of Secondary Battery Cells

Battery vs. Cell

Now, a battery is composed of one or more of these electrochemical cells that are electrically connected to achieve the required operating voltage or current. Therefore, the term “battery” can be used to denote a single-cell or multi-cell battery. In addition to cell components, batteries have various elements, such as control and monitoring components, case/container, cell connectors, markings, and supplementary equipment like fuses, communication systems, as well as cooling and venting systems.

Electric vehicles (EVs) often require more than one battery (or battery module) to achieve the necessary operating voltage and current levels. In such cases, EV battery packs are used. Battery packs are the larger units that house and interconnect multiple modules, providing the overall energy storage for the vehicle, whereas a battery module is a self-contained unit consisting of several individual battery cells. The hierarchy is often as follows: individual cells → modules (batteries) → packs. Learn more information about materials for EV battery packs here.

Flow Battery Components

Conventional batteries, exemplified by lithium-ion batteries, employ fixed anodes and cathodes made of materials like graphite or lithium-containing compounds. They utilize either liquid or solid electrolytes to facilitate ion movement between the anode and cathode, separated by a porous material. A Battery Management System (BMS) is crucial for monitoring and managing various parameters during the charging and discharging processes.

In contrast, redox flow batteries (VRFBs) feature an innovative design. Both the anode and cathode active materials in VRFBs consist of salts dissolved in a liquid electrolyte, eliminating the need for distinct materials. The electrolyte is stored in external tanks, offering scalable energy capacity. An ion exchange membrane (IEM) separates the two electrolyte tanks, allowing protons to pass through while preventing mixing of ions. Multiple cells are combined in a stack, and a pump and flow system circulate the electrolyte between the tanks and through the stack during charging and discharging. This unique design provides advantages in scalability and long cycle life, particularly in applications like grid energy storage.

In vanadium redox flow batteries (VRFBs), the electrodes commonly used are primarily carbon-based. This includes materials like graphite felt, carbon felt, and carbon paper. These carbon-based electrodes serve as crucial components, facilitating the electrochemical reactions and the flow of vanadium ions during the battery's charging and discharging processes. The use of carbon materials contributes to the electrodes' conductivity and durability, making them integral to the overall performance of VRFB systems.

References

¹ Matthias Herrmann; Packaging - Materials review. AIP Conf. Proc. 16 June 2014; 1597 (1): 121–133.

² Weicker, Phillip. (2014). Systems Approach to Lithium-Ion Battery Management - 2.2 Battery Construction. Artech House.

³ What are battery anode and cathode materials? (2023, May 2). Retrieved from https://www.aquametals.com/recyclopedia/lithium-ion-anode-and-cathode-materials/

⁴ Hyebin Jeong, Jooyoung Jang, Changshin Jo, A review on current collector coating methods for next-generation batteries, Chemical Engineering Journal. 2022;  446 (1): 136860

⁵ Boddula, Rajender Inamuddin Pothu, Ramyakrishna Asiri, Abdullah M.. (2020). Rechargeable Batteries - History, Progress, and Applications - 13.3 Classification of Separator in Rechargeable Batteries. John Wiley & Sons.