November 18, 2018

Solid-state Battery Technology

Moein Khaloei

Charging time and range are among the biggest problems faced by most of electric car users. These two problems are highly related to the most expensive component of electric cars, the battery. Modern electric cars such as Tesla Model S can usually travel around 300 miles between charging times, with their lithium-ion battery packs taking a few hours to charge fully.

Sony released the first commercial lithium-ion battery in 1991 thanks to the efforts of Professor John Goodenough and Koichi Mizushima. They demonstrated a 4-volt rechargeable lithium cell using lithium cobalt oxide making lithium-ion batteries commercially possible.

Like all batteries, Lithium-ion batteries include a positive electrode, a negative electrode, and some sort of electrolyte between them. The positive electrode, called a cathode, is made out of lithium oxide. The negative electrode, called an anode, is made out of graphite. The third part consists of electrolytes composed of salts, solvents, and additives serving as the conductive medium for ions to pass between the anode and cathode during the charge and discharge process. The fourth main part is the separator which prevents a short-circuit, so when a battery is charging, lithium ions are released from the cathode, then passed through the separator to the anode where they are stored until the battery is charged. As the battery is being discharged the lithium ions are released from the anode and flow back to the cathode and during both charged and discharged phases electrons pass through the electrical circuit powering the device or charging the battery.

A new generation of batteries called solid-state batteries could double the range of an electric car and be charged in just a few minutes. These batteries are being investigated by various research groups and have not been commercialized yet. Researchers believe that rechargeable solid-state batteries will eventually be cheaper to produce than lithium-ion batteries. They claim that the batteries will be smaller and that the energy density will be much greater. A solid-state battery has the same technology as lithium-ion batteries but instead of having an acid or any liquid in between the positive and negative sides it would put some sort of solid polymer or a ceramic as the electrolyte that would allow the ions to flow.

Unfortunately, the precise characteristics of a solid-state battery for EV use cannot be clearly described yet, because no one has produced such a battery of the appropriate size and cost for an electric vehicle. In this regard, Dr. Milan Rosina, Senior Analyst, Power Electronics & Batteries, within the Power & Wireless division, Yole Développement (Yole) notes:

    “We can describe different approaches, both on materials and manufacturing level, but we need more data from the testing of the whole battery-cell stack and about the design and components of the battery stack (including thermal management, BMS, etc.). It means, we first have to develop a cell stack (fix the choice of materials for electrolyte and electrodes) and manufacturing method, and then we can progress further by optimizing battery-pack design and components.”

Figure 2 shows the development of conventional Lithium-ion batteries and the prediction for solid-state batteries presented by Yole Développement (Yole).

Solid-state batteries could potentially have many advantages over current lithium-ion batteries such as:

• Increased power and energy density
• Reduced size
• Faster charging
• Safer
• Lighter, better performing, more efficient electric cars.
• Easier packaging, since all parts are solid and can be formed into different shapes

The key part to develop solid-state batteries is the electrolyte part of batteries. The electrolytes in lithium-ion batteries are either in liquid form or polymer but electrolytes of solid-state batteries are solid and this is the technology that many companies are investing large amounts of money to develop. There has been a variety of research on materials for solid electrolytes such as ceramics, lithium sulfide and even glass but the key thing is they are solid.

Research for solid-state battery technology has accelerated recently and there is a global race to develop and commercialize it before other teams. Many of the prominent automotive manufacturers and suppliersare working on these new solid-state batteries.

Companies, resources, and brilliant researchers are working on solid-state battery technology. Sakti3 is a company that uses new materials and manufacturing techniques to make solid-state batteries. This company is based out of Michigan and as a subsidiary of the British technology company “Dyson”. They were named among the 50 smartest companies in 2015 by MIT Technology Review and they are working to build a solid-state battery for the electric vehicle that Dyson is planning to develop. Dyson is investing 2 billion pounds or around 2.7 billion dollars in the coming years for the development of three different kind of electric vehicles, and a good amount of that will go to the funding of Sakti3 development of the battery.

In 2014, Sakti3 claimed that they produced the solid-state battery with an energy density of 400 watt hours per kilogram while lithium-ion batteries produced by Panasonic used in Tesla vehicles are believed to have an energy density of 230 watt hours per kilogram. Nevertheless, Sakti3 has been secretive about research and the battery from their announcement was likely small in scale and there are experts in the industry that are skeptical of the company’s claims. It is worth noting that Dyson has experience developing battery technology and producing batteries for various devices. Dyson aims to complete the development of their first electric vehicle and bring it to market equipped with solid-state battery technology by 2020. Their first generations of vehicles will likely run on lithium-ion technology and when Sakti3 is ready to be used, Dyson plans to build a 1 billion dollar battery factory to mass-produce them.

The Nikkei reports that leading Japanese manufacturers have teamed up with the government in a program to develop solid-state batteries. The new program teams the Consortium for Lithium-ion Battery Technology and Evaluation Center (Libtec) with companies such as Toyota Motor, Honda, Nissan and Panasonic. LibTec aims to develop a solid-state battery that would allow an electric vehicle to have a range of 800 kilometers or around 500 miles by 2030. Their short-term goal is to develop a solid-state battery capable of providing a range of 550 kilometers or 340 miles by 2025.

Professor Goodenough has been working on solid-state battery technology too, leading a team at the University of Texas at Austin. In 2017, he claimed that they developed and demonstrated a solid-state battery that would be cheap to produce and has three times the energy density than batteries used today. The team used solid glass electrolytes along with the alkali metal anode.

BMW is confident they will win the race to develop solid state tech. they have recently built the battery Research Center and they also teamed up with “Solid power” a leading developer of solid-state batteries based out of Colorado.

The German automaker, Volkswagen, announced a $100 million investment in 2018 in QuantumScape, a solid-state battery startup that spun out of Stanford. They have been working with since 2012 on solid-state battery technology. They aim to complete development of a solid-state battery by 2025.

Other companies developing this technology include Samsung, Bosch, GM, Fisker, and Mercedes. Although Lithium-ion battery technology has been a big step toward large ranges for electric vehicles, we will need even better battery technology in order to power a future filled with electric cars and electric planes with ranges more than their petrol rivals.