Adden Energy ($5M for solid-sate lithium battery)

Adden Energy develops innovative solid-state battery systems for use in future electric vehicles (EVs). The company’s technology license from Harvard University has enabled it to develop a new type of solid-state battery that can fully charge in just three minutes with over 10,000-lifetime cycles. Adden Energy’s next-gen battery technologies are designed to combat climate change and achieve breakthroughs in the EV industry.

Challenges: lithium battery

Today’s commercially available lithium-ion batteries fall short of what’s needed: safe, long-lasting, and fast charging. Solid-state lithium metal batteries typically use non-flammable solid electrolytes that maintain good ionic conductivity at low temperatures, which would eliminate the most problematic aspect of lithium-ion battery safety and low-temperature performance.

The solid-state battery based on a lithium metal anode paired with  a single crystal LiNi0.8Mn0.1Co0.1O2 (NMC811) particle cathode is of great importance to mobile devices owing to their high capacity and energy density. EVs equipped with these batteries would be able to travel greater distances between charges and be recharged much more quickly than EVs with lithium ion batteries. Prior to their commercialization and practical applications, however, the stability and performance of solid-state lithium metal batteries must be  enhanced.

Adden Energy Technology

Adden Energy develops the technology that enables solid-state lithium metal batteries with high capacity, stable cycling, high-rate, and high current density capabilities, based on the new design principles for electrolytes, interfaces and devices within the framework of the mechanical constriction theory.

The structure of rechargeable battery

The diagram below depicts the structure of Adden Energy’s rechargeable solid-state lithium metal battery. The battery consists of an anode, a cathode, and a multilayer of solid electrolytes disposed between electrodes.

The structure of Adden Energy's battery.
The structure of Adden Energy’s battery.

The anode is composed of lithium metal deposited on a current collector made of copper foil. During battery assembly, a protective layer is applied to the lithium metal to separate the reactive lithium from the first electrolyte layer. The protective layer is a graphite composite film with 5% polytetrafluorethylene (PTFE).

The cathode is a composite film composed of LiNi0.8Mn0.1Co0.1O2 (NMC811) single crystal particles, electrolyte, polymers, and/or carbon black. The composite film is deposited on a current collector made of aluminum foil.

The multiple electrolyte layer consists of a first solid electrolyte, such as Li-argyrodites Li5.5PS4.5Cl1.5 (LPSCl),  and a second solid electrolyte, Li10GeP2S12 (LGPS). The first electrolyte layer separates the second electrolyte layer from the anode. The second electrolyte is less stable than the first solid-state electrolyte towards lithium metal. As shown in the figure below, a separating layer that has the same electrolyte powder as the cathode film is added when the second electrolyte layer is different from that in the cathode film.

An alternative structure of Adden Energy's battery.
An alternative structure of Adden Energy’s battery.

The battery is mechanically constricted by an external pressure between 0.1 MPa and 1,000 MPa. The external pressure may fluctuate periodically during battery cycling through a passive response system or an active response system, e.g., controlled by pressure sensors and programmed electronic devices.

Battery working mechanism

Note that upon cycling the lithium metal and graphite merge quickly to form one dense composite layer. As depicted in the figure below, during charging the lithium ions are extracted from the cathode material, diffuse through solid electrolyte, and deposit as lithium metal on the anode.

The charging of Adden Energy's battery
The charging of Adden Energy’s battery.

During discharging, lithium metal of the anode is oxidized to lithium ions, which diffuse through solid electrolyte and insert into the cathode material, as depicted in the figure below.

The discharging of Adden Energy's battery
The discharging of Adden Energy’s battery.

Key innovations

Mechanical constricted battery

1. High voltage stability of solid-state electrolyte

Ceramic-sulfide solid electrolytes with conductivities of 12–25 mS cm−1 have been reported, which are comparable to or even greater than those of conventional liquid electrolytes. However, the ceramic-sulfide family has a narrow stability window (1.7–2.1 V  vs lithium metal). This limited stability window has proven to be a major barrier for batteries that must operate in a voltage range of approximately 0 to 4 V. New electrolyte systems with larger voltage stability windows are favored by batteries with greater energy density. Li10GeP2S12 (LGPS) is one of the few sulfur-based ceramic solid-state electrolytes that allows batteries to be cycled up to 5 V with minimal degradation.

Adden Energy further expanded the window of LGPS to nearly 10 V versus lithium metal with minimal degradation by simply applying sufficient external mechanical constriction on the battery. Why does mechanical constriction increase the stability of the solid-state system?

LGPS tends to chemically decompose into Li4GeS4 (LGS) and Li3PS4 (LPS) both within the bulk and at cathode material interface.

The volume of the decomposed products is 2% larger than of the original LGPS. Under electrochemical cycling, the volume expansion from electrochemical decompositions is even larger. In fact, the volume increases at the complete oxidation (at high voltage) and reduction (at low voltage) limits can exceed 30%. This increase in volume is referred to as the reaction strain, which is stress-free strain. It does not result from an applied stress – it is solely the result of the electrochemical and/or chemical decomposition that forms products having a different volume than the initial electrolyte.

Small local decompositions in the bulk of LGPS exhibit stress-free reaction strain. However, under sufficient external mechanical constriction, the reaction strain can result in local stresses or pressure. These local stresses are the result of the decomposed products (a larger phase) trying to fit  into the space that was previously occupied by the electrolyte (a smaller phase). As depicted in the figure below, the local stresses experienced by small local decompositions amid rigid mechanical constrictions lead to kinetic stability at the decomposition front where the lithium reordering decreases by a factor of about 10⁶.

High voltage stability of solid electrolyte in Adden Energy's battery
High voltage stability of solid electrolyte in Adden Energy’s battery.
2. Solid electrolyte/cathode interphase stability

The initial contact between solid electrolyte and cathode initiates chemical reactions at the interface, inevitably forming an initial interphase at the interface between solid electrolyte and cathode.

As depicted in the diagram below, the interphase material has a critical threshold modulus denoted by Kcrit. Under an external mechanical constriction, the interphase develops local stresses. A local effective modulus Keff at the interface can be used to characterize the external mechanical constriction level. When Keff is above Kcrit, the interphase is stable throughout cycling. Otherwise, the interphase is unstable and will grow with cycling, thereby limiting the battery performance.

Solid electrolyte cathode interphase stability in Adden Energy's battery
Solid electrolyte cathode interphase stability in Adden Energy’s battery.

In other words, Kcrit indicates how much local mechanical constriction is required to prevent the initial solid electrolyte interphase from decomposing when cycled to the cathode voltage region. A lower Kcrit is therefore preferable, as it reduces the need for external mechanical constriction and simplifies the battery assembly, which could be the determining factor in the commercialization of Adden Energy’s batteries.

3. Anode stability and suppression of reduction

LGPS electrolyte is not stable in direct contact with lithium metal. In addition, LGPS is expected to electrochemically reduce at voltages close to 0 V, resulting in the degradation of battery performance. Moreover, when the current density exceeds the critical current density, voids form and accumulate on the lithium metal/electrolyte interface during battery cycling, which causes a continuous increase of local current density until the threshold for dendrite formation is reached, followed by a short circuit, as shown in the figure below.

Lithium dendrite formation in solid-state lithium metal battery
Lithium dendrite formation in solid-state lithium metal battery.

Adden Energy developed a solid-state battery constructed with a lithium metal with graphite protective layer which separates the lithium metal from the electrolyte, as shown in the figure below. The graphite layer is both lithium metal and LGPS stable. It avoids the initial contact between the lithium metal and electrolyte and prevents (electro-)chemical reactions between them, as well as a short-circuit upon the application of pressure. Mechanical constriction enforces close contact between the electrolyte layer and the lithium/graphite anode. Note that graphite and lithium metal quickly merge to form a composite film upon cycling.

Anode stability with graphite protective layer in Adden Energy's battery
Anode stability with graphite protective layer in Adden Energy’s battery.

Under mechanical constriction, the reduction of LGPS is suppressed and the growth of lithium dendrites is inhibited, resulting in excellent rate and cycling performances. Neither short-circuit nor lithium dendrite formation are observed for batteries cycled at a high current density up to 10 mA cm⁻².

Multilayered solid-state electrolyte

Li5.5PS4.5Cl1.5 (LPSCl) is more stable with lithium metal compared to LGPS. Even so, a graphite protection layer is typically applied to insulate the contact between LPSCl and lithium metal. Without such protection, the battery may fail due to a subsequent short circuit caused by the lithium dendrite penetration.

Adden Energy advanced the solid-state lithium metal battery with multiple electrolyte layers, as shown in the figure below, in which an electrolyte layer of LPSCl is inserted between the anode of lithium metal/graphite and LGPS electrolyte layer.  The LPSCl layer is in direct contact with the graphite-protected lithium metal in order to (electro)chemically protect the interface. The addition of the LGPS layer to the system greatly improves the cycling performance of the battery. This result indicates that such an electrochemically less stable solid electrolyte with lithium metal can block the lithium dendrite penetration. The mechanism is illustrated in the figure below.

A multilayer of solid electrolytes in Adden Energy's battery
A multilayer of solid electrolytes in Adden Energy’s battery.

During cycling, only the LPSCl layer develops cracks where lithium dendrites penetrate, while the LGPS layer has no cracks. But local decompositions occur in LGPS. A sufficient external mechanical constriction provides metastability and kinetic stability at the decomposition front. This well constrained decomposition may serve as a self-healing ‘concrete’ to fill and heal any micrometer- or submicrometer-sized cracks, either pre-existing during the battery assembly or having emerged during the battery cycling, to inhibit the lithium dendrite penetration.

Battery perfromance

Adden Energy created mechanically constricted solid state batteries with graphene-protected lithium metal anode, a multilayer of solid electrolytes, and LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode. The cycling performance of the battery is demonstrated to be very stable, with 82% capacity retention after 10,000 cycles at 20 C (70% capacity retention after 9,300 cycles at 15 C). The average Coulombic efficiency is 99.96% at 20 C among all the thousands of cycles, with the highest power density reaching 11.9 kW/kg and the energy density up to 631 Wh/kg at the cathode active material level.

Adden Energy Patent

  • US20200350618A1 Solid state electrolytes and methods of production thereof
  • US20210408580A1 Solid state batteries
  • WO2020018790A1 Metal coated structures for use as electrodes for batteries and methods of production thereof
  • WO2022094412A1 Batteries with solid state electrolyte multilayers

Adden Energy Products

Adden Energy is developing and scaling up this brand-new type of solid-state battery. With demonstrated charge times as low as 3 minutes and capacity retention for over 10,000 cycles in a lab-scale cell, Adden Energy is developing cutting edge technologies to enable mass adoption of EVs around the world and contribute greatly to a cleaner future.

Solid-state lithium metal battery of Adden Energy.
Solid-state lithium metal battery of Adden Energy.

Adden Energy Funding

Adden Energy has raised a total of $5.2M in funding over 1 round. This was a Seed round raised on Feb 25, 2022.

Adden Energy Investors

Adden Energy is funded by 3 investors, including Rhapsody Venture Partners, MassVentures, and Primavera Capital Group. Rhapsody Venture Partners and MassVentures are the most recent investors.

Adden Energy Founder

William Fitzhugh, Luhan Ye, Fred Hu, and Xin Li are Co-founders.

Adden Energy CEO

William Fitzhugh is CEO.

Adden Energy Board Member and Advisor

Fred Hu and Xin Li are board members.

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