The PolyPlus Protected Lithium Electrode

+ Protected Lithium Electrode

Protected Lithium Electrode. The Protected Lithium Electrode (PLE) is a free-standing battery anode with a lithium metal core that enables the development of safe batteries with unprecedented energy densities. The PLE was recognized by TIME magazine as one of the 50 Best Inventions of 2011, and by the Edison Committee with a Gold Edison Award in 2012.

What is it?

The PolyPlus PLE is a sheet of metallic lithium protected by a thin, dense, inorganic membrane that selectively conducts Li+ ions. The PLE makes possible what was thought to be impossible: to build batteries that combine lithium metal electrodes with water-based chemistries.

Technical Significance

Highest Energy Density

The PolyPlus PLE is the world’s first air-stable lithium metal electrode, and it has enabled the design and fabrication of the most compact and energy dense batteries.

Proven Performance

World-record performance of PolyPlus Li-Air cells has been verified by the U.S. Army CERDEC. Testing at their Aberdeen facility confirmed specific energy in excess of 800 Wh/kg for 10 Ah PolyPlus Li-Air cells.

Paradigm Shift for Battery Design

The PolyPlus PLE concept changes the way we think about battery cell design.

The membrane functions as an engineered solid electrolyte interface.

The PLE decouples the negative lithium electrode from chemical environment of the battery, allowing pairing of the PLE with unconventional electrolytes and high-voltage positive electrodes.

The Future

The invention of the PLE by PolyPlus enables the development of a new generation of battery chemistries. PolyPlus worked with a Tier 1 battery manufacturing engineering firm to design and build a first of its kind pilot line to produce the protected lithium electrodes used in state-of-the-art lithium-air, lithium-water, and lithium-sulfur batteries. PolyPlus is now refining the PLE to enable the manufacture of ultra-compact/ultra-light batteries that can be scaled to volumes that will satisfy the global marketplace.

The PolyPlus Lithium-Air Battery

+ Lithium Air

Lithium Air. To build the world’s lightest primary battery, PolyPlus couples the lithium metal in the PLE with a gas diffusion electrode, aqueous electrolyte, and ambient air. The Li-Air battery is ideal for weight-sensitive, portable power applications.

What is it?

A battery that runs on air. The PolyPlus Li-Air battery is constructed by sandwiching the PLE between two cathodes in compartments specially engineered to admit air, electrochemically reduce the oxygen, and store the reaction products.

Technical Significance

Ultra-lightweight, portable energy

The cell-level energy density of PolyPlus’ Li-Air batteries is > 800 Wh/kg. Pack level batteries deliver >500 Wh/kg.


Since the cathode for the PolyPlus Li-Air battery is water-based and uses air from the surrounding environment, the battery contains no toxic chemicals (SOCl2, SO2, CFx).

Long Shelf Life

The solid-state PLE membrane prevents parasitic side reactions; therefore the PolyPlus Li-Air batteries have a low self-discharge rate and a projected shelf life of >10 years.


Since PolyPlus Li-Air batteries use aqueous electrolytes and air electrodes, the projected costs at high volumes are very competitive with existing battery technologies.

The Future

Lithium-air batteries are most attractive for those applications that are particularly weight sensitive, including but not limited to soldier power and remote sensors. PolyPlus has demonstrated world records levels of specific energy (800 Wh/kg) for its existing 10 Ah Li-Air cells, and is now working to boost the power density of its Li-Air cells. We expect to start manufacturing Li-Air cells within the next year.

The PolyPlus Lithium-Water Battery

+ Lithium Water

Lithium Water. PolyPlus developed the first water-activated lithium batteries by coupling the PLE with one of several water-activated cathodes. During use, the batteries are open to the seawater environment. The Li-water battery is ultra-lightweight and ideal for long-life, underwater power.

What is it?

A battery that runs on water.

PolyPlus’ Li-Seawater batteries pair the Protected Lithium Electrode with various cathodes depending on the intended application and marine environment. The positive electrode can electrochemically reduce oxygen dissolved in seawater for the highest possible energy density [Type Ia], or it can electrochemically reduce seawater, producing hydrogen in the process [Type Ib]. Alternatively, a proprietary cathode can be used for higher rate applications [Type II].

PolyPlus’ Type I Li-Seawater batteries have achieved 1300 Wh/kg, while the Type II Li-Seawater batteries give 400 Wh/kg and 600 Wh/l.

Technical Significance

Ultra-lightweight, compact, underwater energy source

PolyPlus’ Li-Seawater batteries can pack a large amount of energy into a small amount of space. Type Ia and Ib are also close to neutral buoyancy.

Long lifetime

The Li-Seawater batteries are ideal for long duration, low-power applications due to the slow, controlled release of lithium through the PLE’s protective layer. As with all PolyPlus PLE-based batteries, the self-discharge rate of the battery is effectively zero.

Pressure tolerant

PLEs have been discharged in the lab after having been subjected to isostatic pressures up to 10,000 psi. PLEs have also been subjected to 2500psi in saltwater and discharged with no ill effects. For deep water use, the Li-Seawater batteries do not need to be housed in bulky, expensive, protective pressure vessels.

Safe, non-toxic

PolyPlus Li-Seawater batteries are not actually batteries until they are deployed, and therefore are far safer than competing high energy density chemistries. In contrast to most commercially available high energy density batteries, no toxic chemicals are used in the Li-Seawater batteries and consequently they present no longterm environmental hazard to marine life.

The Future

Interest in batteries for marine applications is growing rapidly, largely due to the advent of autonomous vehicles for oceanographic, commercial, and military applications. The extremely high energy density and of PolyPlus Li-Seawater batteries combined with their safety make them a compelling choice for marine applications needing the ultimate in energy density.

Aqueous Polysulfides used in the PolyPlus Lithium-Sulfur Battery

+ Lithium Sulfur

Lithium Sulfur. PolyPlus is developing ultra-lightweight rechargeable batteries using water-based Li-S chemistry. Compared to today’s Li-ion batteries, PolyPlus’ Li-S battery will pack the same amount of energy into the same amount of space, but at half the weight.

What is it?

A lighter weight, rechargeable battery to replace Li-ion batteries.

PolyPlus’ aqueous Li-S battery pairs the PLE as the negative electrode with a water-based solution of sulfur as the positive electrode.

Sulfur has almost ten times the capacity of positive electrode materials used in Li-ion batteries, and is orders of magnitude less expensive. The conventional approach to rechargeable Li-S batteries is based on the use of non-aqueous electrolytes and unprotected lithium metal foil, leading to lightweight batteries with a high rate of self-discharge, questionable safety, and poor cycle life.

In contrast, PolyPlus builds its cell with protected lithium and aqueous electrolytes, leading to rechargeable Li-S cells with excellent cycle life, safe operation, and no evidence of self-discharge.

Technical Significance

Lightweight rechargeable batteries

The projected performance of rechargeable Li-S cells is over 400 Wh/kg and 600 Wh/l. With a specific energy that is twice that of competing Li-ion technology, Li-S batteries will be attractive for weight sensitive applications.

Long cycle life

Using the protected lithium electrode in the Li-S cell solves the commonly observed cycle life problem. PolyPlus’ Li-S cells cycle hundreds of times without significant capacity loss.

Reduced materials costs

Sulfur is one of the most abundant elements on earth, and is priced accordingly. Although Li-ion battery prices have dropped significantly over the past several years, they still present a cost hurdle for widespread adoption of electric vehicles. The introduction of lightweight rechargeable Li-S batteries presents an attractive alternative to Li-ion technology, that in the long run should reduce the cost of EV ownership.

The Future

Rechargeable Li-S batteries are still in development at PolyPlus. Initial commercialization will be focused on high margin applications where weight is a premium. PolyPlus will likely work with a partner and/or license the technology for high volume, cost-sensitive markets.