Lithium-Ion Batteries: Basics and Applications

Electrochemical storage systems will increasingly gain in importance in the future. This is true for the energy supply of computers and mobile phones that are becoming more and more sophisticated and smaller. It is also true for power tools and electric vehicles as well as, on a larger scale, for stationary storage of renewable energy. This Chapter will provide an overview of today's most common electrochemical storage systems. It will discuss two primary systems, which in general cannot be recharged, or only in limited fashion. Among other things, problems of rechargeability are discussed, using the example of the anode materials zinc (for aqueous electrolytes) and lithium (for non-aqueous electrolytes). In terms of rechargeable systems, the whole spectrum from lead-acid batteries to rechargeable nickel-based or sodium-based batteries to lithium-ion batteries is covered. Redox flow-batteries also are discussed, as are electric double-layer capacitors. This will enable the reader to gain an insight in the lithium-ion technology's competing and complementary technologies. The latter will be presented in other chapters of this book.

The history of lithium-ion batteries started in 1962. The first battery was a battery that could not be recharged after the initial discharging (primary battery). The materials were lithium for the negative electrode and manganese dioxide for the positive electrode. This battery was introduced on the market by Sanyo in 1972. Moli Energy developed the first rechargeable battery (secondary battery) in 1985. This battery was based on lithium (negative electrode) and molybdenum sulfide (positive electrode). However, its design exhibited safety problems due to the lithium on the negative electrode.

Lithium-ion batteries are hi-tech devices made of complex high-purity chemicals and other raw materials. The following chapters aim to give a comprehensive picture of these materials and their functions. One might think that the lithium-ion battery is lightweight due to the small mass of its main component, lithium. However, this is not quite true: only 2% of the battery mass is lithium, the rest being electrode materials, electrolyte, and inactive structural components.

Lithium transition metal compounds are employed as cathode materials. These composites can develop mixed crystals over an ample composition range and can deintercalate lithium ions from the structure during the charging process. The transition metal ions are oxidized because of the charge neutrality and therefore the oxidation state of the transition metal cation is elevated. Lithium is deintercalated while the battery is discharging, which in turn reduces the transition metal ions and decreases the oxidation number.

Secondary lithium cells initially had a metallic lithium foil as an anode (negative electrode) [1]. Pure lithium has a very high specific capacity (3,860 mAh/g) and a very negative potential, resulting in very high cell voltage. However, cycling efficiency decreases as lithium dissolves repeatedly while the cell is discharging and lithium is deposited as it is charging. This means that two or three times the normal amount of lithium must be used. In addition, lithium can be deposited as foam and as dendrites. The latter might grow through the separator [2, 3]. These dendrites can cause local short circuits, which might result in the cell completely self-discharging or, in the worst case, lead to an internal thermal chain reaction, fire, or explosion.

The development of new electrolyte systems for lithium-ion batteries is of paramount importance, alongside the development of new electrode materials and separators. Lithium-ion battery electrolytes are more than colorless fluids that merely keep up the transport of ions between the electrodes. Today, they are high-purity multi-component systems with a multitude of requirements and tasks.

Battery separators are flat materials situated between the positive and negative electrodes of a battery cell. Their function is to prevent physical contact and, therefore, short circuits. At the same time, they must enable ions to be transported as freely as possible within the electrolyte between the electrodes. This is essential for charge equalization and the electrochemical cell to work. To achieve this, separators are usually porous flat designs filled with an electrolyte. The following chapters first set out the basic characteristics of separators and the current status of conventional separator technology. Then, new separator concepts will be outlined and a currently available separator technology and its characteristics will be presented.

The design of a battery system should ensure that an energy storage system operates efficiently, reliably, and safely during vehicle deployment for a very long period of time. Lithium-ion cells are the fundamental components of lithium-ion battery systems and they impose special requirements on battery design. Aside from electrochemical storage cells, the battery system comprises a multitude of mechanical, electrical, and electronic components with functions that need to be perfectly balanced. The electronic battery management system (BMS) not only monitors and controls the battery, it also provides data communication to the vehicle.

Lithium-ion technology has become indispensable in everyday life. A lot of devices are powered by lithium-ion cells nowadays. The following will discuss history, cell materials, cell electrodes, cell designs, market overview, applications, technology, requirements, trends, and further reading.

Lithium batteries dominate today's consumer market. In the year 2014, around two billion lithium cells were produced for cell phones only. Off-the-shelf usage of lithium-based battery systems in vehicles began in the year 2009 with Daimler AG's S400 hybrid. In 2011, the first purely electric vehicles with lithium batteries were produced in series. As of today, all battery-driven and plug-in hybrid vehicles contain lithium-based energy storage systems. Table 10.1 compares consumer lithium batteries with automotive lithium batteries.

Lithium-ion batteries as an energy storage system represent one of the essential technological components in an electric vehicle and are the biggest expense factor. Therefore, measurement of state variables such as state of charge (SOC), state of health (SOH), and state of function (SOF) fulfills several requirements. Safety-relevant functions need to ensure protection against overcharging or deep discharging, for example. In addition, optimal utilization of the battery capacity is of great economic importance.

Electromechanical relays have always reliably switched electrical loads in automobiles. The special operating conditions of vehicles with a combustion engine already necessitate a special requirement profile for these relays. Their use in vehicles with electrical power trains requires these components to meet totally new demands. The voltage level in these vehicles is usually much higher, which plays an essential role in this respect. Combustion engine-driven cars have had a standard system voltage of 12 V or 24 V for many decades. The system voltage for hybrid and electric vehicles is generally several hundred volts. Commercial vehicles even have batteries up to 1,000 V.

A lithium-ion battery for mobile applications needs efficient thermal management to guarantee the required service life of more than 10 years as well as full performance and availability under all operating and environmental conditions. Thermal management comprises cooling as well as heating. Lithium-ion batteries are available in a multitude of variants, with considerably differing cell chemistry and design. Thermal management therefore must be adapted to the respective variant’s requirements. This also applies to the large number of different vehicle applications, ranging from the subcompact car to the sports car and from the low-level hybrid vehicle to the entirely electricity-driven vehicle. These different types impose different thermal management requirements on the drive battery. Integration into the vehicle’s Thermal management also plays an important role. The car manufacturers pursue approaches that vary immensely.

The battery management system's most important task is to protect the drive battery's individual cells and to increase service life as well as cycle numbers. This is especially important for lithium-ion technology because the batteries must be protected from overcharging and excess temperature (Fig. 14.1) to prevent cell destruction.

The growing number of control units in cars and their increasing networking make car electronics more and more complex. Also, car manufacturers face the challenge of having to cut design cycles and reduce costs. As a result, quick and cost-efficient software development methodology is becoming essential. The software for lithium-ion batteries is located in distributed systems and it also has elements that are critical for safety, which generates additional requirements.

Rechargeable lithium-ion batteries have been continually developed since their introduction by Sony in 1991. Energy density is one of the key parameters for lithium-ion batteries. It was steadily increased by optimizing battery components such as electrode materials or electrolyte as well as by improving the cell construction technologies. The cell level progress during recent years is shown in Fig. 16.1. Both gravimetric (specific) and volumetric energy density were more than doubled.

Lithium-ion batteries for electric mobility applications consist of battery modules made up of many individual battery cells (Fig. 17.1). The number of battery modules depends on the application. The modules are installed in a lithium-ion battery together with a battery management system, a cooling system, temperature management, and power electronics. Different cell types can be used in battery modules; they include round cells, prismatic hardcase cells, or flat cells such as coffee bag cells or pouch cells (more detailed information available in Chapter 9).

This Chapter describes the set-up of a battery production plant. The required manufacturing environment (clean/dry rooms), media supply, utilities, and building facilities are described, using the manufacturing process and equipment as a starting point. The high-level intra-building logistics and the allocation of areas are outlined. Lastly, the Chapter offers an outlook on future challenges and development potential.

Lithium-ion cell production processes, starting with the active materials, always have high vertical integration rates. Therefore control processes are required in as many production steps as possible.

Producing lithium-ion batteries is a complex technical process consisting of multiple steps that have to be seamlessly integrated. A perfect cell can – but does not have to – result in the most suitable battery for the respective application. The specific application has to be taken into account in the cell design stage. All steps in the production process require a high standard of diligence, which can only be achieved with implementing state-of-the-art, safe production methods.

It has been repeatedly shown that the usage of lithium-ion batteries can harbor dangerous surprises, for example, in an incident in which a car battery caught fire several weeks after testing [1]. In addition to ensuring the safety of end users, this new storage technology poses new challenges in regard to occupational health and safety in industrial applications.

Unlike other battery types such as lead-acid, nickel-cadmium, and nickel metal hydride, today’s standard lithium batteries, by definition, must not trigger secondary reactions apart from those during charging and discharging. Secondary reactions in standard batteries allow overcharging in the form of gassing (electrolyte degradation), for instance. In closed systems, this causes a temperature increase due to the oxygen cycle, but not a system failure. In lithium batteries, overcharging also results in electrolyte degradation, but the process is irreversible and leads to system failure.

Due to continuous development in various areas of application for storage batteries, the demand for energy storage systems with high energy density is growing rapidly. The market requires energy supply systems that are increasingly based on renewable energies in order to make mobility less dependent on fossil fuels.

In the past fifteen years, the number of electronic systems in vehicles has increased considerably. In the 1980s, most vehicles did not even have airbags, let alone electronic stability programs (ESP). Today, highly complex electronic safety systems have become increasingly widespread. Systems relevant to safety such as ABS, ESP, or active steering have demonstrably reduced the number of road fatalities and injuries. However, although these systems are clearly beneficial, if they do not function according to the specifications, they are not only rendered ineffective, but can even cause dangerous driving situations. “Functional safety” is an instrument that identifies and prevents dangerous situations on the road.

Functional and safety tests for lithium-ion batteries used in industrial applications are essential. Fig. 8.3 shows a diagram of such batteries. The battery consists of individual cells interconnected to form modules. Several modules are then also interconnected inside the battery itself. The battery also features a cooling circuit. A deaeration system evacuates gases during cell outgassing. The battery housing contains the battery management system (BMS) and the circuit interrupter.

Lithium batteries were introduced on the market in the seventies and were produced for special applications in relatively small lot sizes. Today, billions of rechargeable lithium-based batteries are transported every year.

After a long hiatus, research on electric vehicles with battery energy storage systems was taken up again in the early 1980s. Developing low-cost batteries with a high power and energy density was and still is an important focus of such research. Lithium-ion batteries, which currently dominate in many consumer electronics applications such as laptops, represent a battery type that is able to achieve an acceptable range of up to 250 km in electric vehicles with a “still acceptable” battery weight of around 300 kg. For several years now, intensive research to further improve this technology has been promoted in both the private and the public sector.

Modern qualification concepts enable battery manufacturers to react dynamically to technical challenges and to familiarize new staff with the latest company processes early on. Also, they can qualify their skilled personnel to work with new technologies and changed processes and tasks by implementing company-specific vocational training and continuing education, which is integrated into the company's processes and adapted to the personnel's individual talents and interests.

Today, standards are the foundation of almost all technical developments. They are the basis for companies that want to penetrate national and international markets and they also provide legal certainty. In our society, standards ensure trust and safety and bundle developers’ resources in order to create safe and manageable products in a goal-oriented manner.

Due to ever-growing energy requirements, the world’s population is dependent on fossil energy sources, which will result in a shortage of these resources and possible climate changes. It is widely recognized that energy production increasingly needs to be covered by renewable energy sources. This trend has been fueled by the rapid economic growth of the so-called emerging countries and the decision by some industrial nations to phase out nuclear energy production. The increased use of renewable energies, such as solar and wind power, has ultimately resulted in the necessity to store electric power temporarily in order to bridge the gap between the time of producing energy and consuming it. Batteries can provide part of the required capacity, ranging from battery units for homes with several kWh of storage capacity through to large batteries with capacities in the MWh range suitable as grid storage systems. Other systems such as pump storage systems or compressed-air storage systems already exist, but can only be expanded to a limited extent because they require a specific geographical environment. In addition, other electrochemical storage systems are currently being applied or developed in the stationary battery system segment such as high-temperature batteries and redox-flow systems.

Future mobility needs novel concepts that strike a balance between individual mobility needs, sustainable use of resources, and protection of the environment (Fig. 31.1). Also, owing to climate change and the limitation of fossil fuels, more efforts are required to decrease CO₂ emissions. In this regard, the entire automotive industry has already achieved considerable success by optimizing engine technology and introducing automatic engine start/stop systems and brake energy recuperation. These efforts in conventional drive technology are ongoing.

Considerable structural changes are needed in public power grids to promote the use of renewable energies and increase in their share in electricity production and introduce and implement climate protection measures. Decentralized energy conversion systems (e.g., photovoltaics, wind power) must be incorporated into the power grid. Another challenge in planning and management is the interaction of existing facilities with the decentralized production and storage units to be incorporated. Stationary energy storage systems will become more important over the coming years, because there will be a need to manage a great number of fluctuating and decentralized energy generating plants. Electrochemical storage systems, consisting of cells or batteries, will be essential in this respect.