The next step change in battery-tech; a solid state battery deep dive

July 30, 2018

Improved battery availability and performance are essential to the growth of electric vehicle and renewable energy business models. Isabelle, Repower Group spring 2018 MBA intern, wrote a guest piece for our blog about advances in battery tech.


Special thanks to Dean Frankel and Thomas Yu for providing their points of view as well!




Growing demand of electric vehicles and renewable energy is increasing the demand for rechargeable batteries.


Lithium-ion batteries have emerged as the most prevalent energy storage technology in consumer electronics, grid-tied energy storage, and electric vehicles due to their characteristics of having longer lifespans, lower self-discharge, and lighter weight compared to nickel- or lead-based batteries. As demand and production capacity grow, the technology will continue to achieve significant improvements in cost at scale. However, Li-ion batteries still face limitations, including raw material (in particular cobalt) availability, slow charging speed, and safety concerns. Numerous research institutions and enterprises are searching for an alternative to Li-ion batteries to address these shortcomings. In this post, we will explore one technology that some experts believe is a better solution: solid-state batteries (SSBs).


Technology Overview


Solid-state batteries replace the liquid electrolyte in Li-ion batteries with a solid electrolyte. Historically, conducting ions through a solid material has been difficult; but in the last 10 years, there have been technology breakthroughs that increased the ionic conductivity to levels that are sufficient to support EV performance at room temperatures.


The graphic below compares the material composition of Li-ion and SSBs. The Li-ion architecture typically consists of a cathode, separator, and carbon graphite anode. SSB replaces the separator with a solid electrolyte that conducts ions between the anode and cathode. The solid electrolyte can be classified into two categories: organic (polymers) and inorganic (oxides, phosphates, and sulfides). The solid electrolyte enables the use of high voltage cathodes and anodes – the graphite anode in the Li-ion battery can be replaced with a metallic lithium anode, which has 10x greater energy potential, resulting in the benefit of using less material for greater energy storage capacity.


Advantages & Disadvantages


SSBs combine two attributes that are difficult to achieve by Li-ion batteries, but are critical for EV applications: safety and high energy density. By eliminating the liquid electrolyte in Li-ion batteries (organic solvents such as ethylene carbonate, dimethyl carbonate), solid-state batteries are significantly safer. Additionally, since there is no risk of thermal events, SSBs do not require any cooling system, thus they weigh less and require less space.


Where the technology demonstrate the biggest promise is its enhanced energy density. SSBs enable the use of higher potential cathodes and lithium metal as the anode, and can results in 3-5x improvements in energy density (energy stored per mass, measured in Wh/kg).


SSBs' most significant challenge is low temperature operations, as ionic mobility through solid materials decreases with temperature. Most SSBs charge at a slower pace when the battery internal temperature is below 70C. Scientists and researchers are still addressing these technical limitations.




SSB technology is currently still in the R&D and prototype phases, with some companies like Toyota seeking to commercialize in the 2020's. Similar to other manufacturing-intensive hardware, SSBs have to take a two- step approach to commercialization:

  1. First, manufacturers produce a battery targeting niche markets where the critical requirements are high energy density and safety (instead of cost), such as aerospace and military. The cost per kWh may be several times greater than current Li-ion batteries.

  2. As technology improves, market matures, and production increases, manufacturers create a cost-competitive battery targeting the broader electric vehicle and consumer electronic markets.

While SSBs have been traditionally expensive to produce, the manufacturing cost is a hurdle that can be overcome. The costs will eventually decrease as scale increases, similar to how Li-ion battery costs decreased from $1000/kWh in 2010 to $210/kWh in 2017. Nonetheless, road to commercialization continues to be a complex and long one. While there is uncertainty to when commercialization will occur, academic institutions, OEMs, and start-ups have already collaborated to make significant investments in this space.


Key Commercial Investments

  • Toyota plans to have production-ready SSBs in the early 2020's.

  • BMW is partnering with Solid Power, a Colorado start-up developing sulfide-based solid electrolyte.

  • Volkswagen invested $100 million and a formed joint venture with QuantumScape, a Stanford spin-off startup developing SSBs with oxide electrolyte. (

  • Hyundai is investing in Ionic Materials, a Massachusetts based startup developing SSBs with a polymer electrolyte. (

  • SAIC Motors and General Motors invested in MIT spin-off SolidEnergy that develops semi-solid state batteries (




Isabelle Ji was a rock star MBA intern for Repower Group during her Spring 2018 semester at Wharton, the University of Pennsylvania's business school.  She has a background in consulting and environmental & chemical engineering and a passion for applying cutting-edge technologies to advance innovation in the sustainability and mobility space.


Repower Group invests in the debt, equity, and assets of companies at the intersection of new mobility and energy.




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