Batteries leading the charge in energy storage 

Batteries are devices that provide energy storage and release it on demand. While the everyday batteries generate electrical energy through the direct conversion of chemical energy, the energy storage concept is illustrated well by the Nant de Drance pumped storage “water battery”. Located high in the Swiss Alps, it contains an electric storage capacity surpassing that of 400,000 electric car batteries.

This water battery operates using hydroelectric generators and dual reservoirs, one upper and one lower. During peak hours, water from the higher-altitude reservoir is released to generate electricity. When there is energy overproduction, the water is pumped back up and stored for future use. 

While a fascinating model, the water battery differs, from common, portable batteries used to power significant portions of everyday modern life. Conventional batteries are electrochemical cells or series of cells that produce electric current. 

Few technologies are more important in the industry’s quest to reduce carbon dioxide emissions than electrochemical batteries. They power electric vehicles, store electricity from solar panels and wind turbines, and stabilize the electric grid. In the latter two applications, batteries are essential to economically scale up renewable energy sources. 

Given the unique environmental impact of batteries, including mining, disposal and the entire lifecycle of production requires a thorough analysis. This ensures that the energy transition does not exchange one set of problems for the environment for another equally as damaging.

Electrochemical cell batteries are categorized into three main classes: primary, secondary and tertiary, with various cell constructions within these broad categories. The use of different metals and electrolytes within these classifications provide properties suited for various end uses.

Also known as single-use batteries, primary cell batteries cannot be recharged and must be disposed of after use. They are often used in portable devices like flashlights and other large electronics. Examples include dry cells, alkaline batteries, zinc-carbon cells and lithium primary cells.

Alkaline batteries are the most popular type of single-use battery. The most economical category, these non-rechargeable batteries maintain a consistent discharge rate throughout their lifetime and provide reliable performance. However, while convenient, alkaline batteries are not environmentally friendly due to their single-use nature.

Rechargeable batteries, otherwise referred to as secondary batteries, can be recharged and reused multiple times. Unlike primary batteries designed for single-use, they use external electric potential to reverse the discharge chemical reaction, allowing for multiple uses. These cells come in various chemistry configurations, including lead-acid, nickel-cadmium (Ni-Cd), nickel–metal hydride (Ni-MH) and lithium-ion (Li-ion). Rechargeable batteries are generally more expensive than primary batteries and some require proper handling to prevent overheating, which could potentially cause a fire or explosion.

Tertiary batteries are the least common type of battery. Unlike primary and secondary batteries, their cells are separated from other components until just before activation. The electrolyte is the most frequently isolated component.

Reserve batteries effectively eliminate the possibility of self-discharge and minimize chemical deterioration. Most reserve batteries are thermal type and they are used almost exclusively in military applications.

The remainder of this article will focus on rechargeable lithium-ion (Li-ion) batteries, which are the most common type.

Li-ion batteries are preferred type for use in a broad array of applications due to their long-life, high-energy density and desirable voltage characteristics. The long list includes tiny hearing aids, cell phones, computers, e-bikes, electric vehicles and even massive grid-scale energy storage.

Li-ion batteries typically use different materials for the anode (negative electrode) and cathode (positive electrode). Any conducting material, including metals, semiconductors, graphite or conductive polymers can be used as an electrode.

Positive electrode materials significantly affect performance, cycling and life of Li-ion cells. The electrolyte carries positively charged lithium-ions between the anode and cathode, while the separator blocks the flow of electrons inside the battery, allowing lithium-ions to pass through.

At the negatively charged anode, an oxidation reaction occurs and releases electrons that move toward the external part of the circuit. Most lithium-ion batteries use a mixture of graphite as an anode material — a combination of natural graphite mined from the earth and synthetic graphite, derived from heating petroleum coke. The resultant mixture has a layered structure, allowing lithium ions to enter the layers during charging and exit during discharge.

The cathode is the positive electrode of a cell where a reductive chemical reaction occurs. Li–ion batteries use various cathode materials, including lithium cobalt oxide, lithium iron phosphate and lithium nickel manganese cobalt oxide. These materials can reversibly accept and eject lithium ions into and out of their crystal structure during charge and discharge cycles.

Li-ion battery manufacturers must obtain high quality minerals of exceptional purity. Consequently, more than half the cost of manufacturing Li-ion batteries resides in the cathode and anode. Assembling the cathode, separator, anodes and current collectors also requires precise assembly steps, including placement of individual layers and wrapping.

Li-ion batteries have been around for about 30 years and have seen exponential growth during that period.

However, other rechargeable battery chemistries, such as lead-acid, Ni-Cd and Ni-MH, have existed for over a century. Each of them has its own advantages and disadvantages, as noted in the following sections.

Lead-acid batteries have been around since the late 1800s and are still widely used today. These batteries are cost-effective, recyclable and do not require complex battery management systems for maintenance. However, they have a low specific energy and limited cycle count relative to other types. Lead-acid batteries are used to power wheelchairs, golf carts, emergency lighting and cars with internal combustion engines. Due to the presence of lead, a known toxin, they must be professionally disposed of at the end of their useful life.

Ni-Cd batteries consist of nickel oxide hydroxide, metallic cadmium electrodes and an alkaline potassium hydroxide electrolyte. One of their primary benefits is the potential for rapid charging, but the accompanying drawback is a high self-discharge rate. Additionally, cadmium, such as lead, is toxic.

Ni-MH batteries provide incremental improvements over Ni-Cd, including a 30% increase in charge density per volume and much slower self-discharge. However, they take longer to charge and they are especially prone to capacity degradation with repeated recharging.

Compared to the other secondary battery chemistries, Li-ion batteries are a modern rechargeable development. They exhibit an unmatched combination of high energy and power density, along with a superior weight-to-energy ratio when compared to the preceding three types. However, Li-ion batteries are extremely flammable, necessitating a protection circuit and cautious handling.

New generations of advanced Li-ion batteries are expected on the near horizon. For example, lithium-sulfur batteries, where the lithium anode is consumed and sulfur is transformed into a variety of chemical compounds. Solid-state batteries also have potential, but this concept has yet to move from the lab to commercial viability.

Amid our great energy transition, the future of batteries impacts us all. This includes the materials used, where the metals are sourced and mined and how these minerals are disposed of, or ideally reused. Sustainable battery development must consider the criticality of raw materials and give deserving reflection to sourcing, disposal and the eventual reuse of these minerals.