OXIS Technology

Technology

OXIS has successfully developed a Polymer Lithium Sulphur (Li-S) based battery technology platform using:

• A Lithium Metal anode
• A Sulphur-based cathode
• A Lithium Sulphide electrolyte rendering inherently safe Lithium Metal

The key strengths of the technology are:

• Superior energy density
• Light
• Inherently safe

Superior Energy Density

Systems using metallic Lithium are known to offer the highest specific energy. Sulphur represents a natural ‘cathode partner’ for metallic Li and a Lithium-Sulphur couple has theoretical specific energy in excess of 2700Wh/kg, which is nearly 5 times higher than that of Li-ion.

OXIS’s next generation lithium technology platform offers the highest energy density among lithium chemistry:

• 300 Wh/kg demonstrated in 2010 vs. 140 Wh/kg for most safe conventional lithium-ion chemistry
• 460 to 600 Wh/kg target in 2016 vs. 215 Wh/kg for the most promising mainstream lithium technology, which is unlikely to meet the highest standards of safety required by the automotive industry
  

History of battery technology development

Therefore for the same energy requirements, a lighter battery can be used

Electric vehicle batteries: OXIS Li-S v Li-ion
Comparison of a 1,000kg car with a 500kg Li-ion battery

Safety

(a) When the use of Li metal may be risky

Conventional electrochemical wisdom holds that the use of Lithium metal is risky. Indeed, even Li-ion batteries suffer major safety concerns associated with the growth of spiky Lithium dendrites resulting in an internal short circuit, followed by uncontrolled energy release. A common belief is that any rechargeable Lithium metal system would sooner or later generate uncontrolled dendritic Lithium.

(b) Oxis: Li is safe to use in Polymer Li-S systems

Fortunately, this is not the case for the Li-S battery of OXIS Energy. Lithium Sulphur electrolytes provide an effective mechanism for the passivation of suspended or ‘mossy' Lithium by creating instantaneously a
(Li2S) film on metallic Lithium. Passivated Lithium that forms during charge is dissolved during discharge or battery rest periods. This inherent protection mechanism is supported on the chemical level and is associated with the so called ‘Sulphide cycle’. Lithium Sulphur (Li2S) has a melting point of 938°C and is a perfect insulator. The failure mode for Oxis’s Li-metal battery is the loss of capacity due to formation between electrodes of non-conductive and highly stable passivated lithium sulphide.

OXIS’s batteries use ‘heavy’ electrolytes with high flash points. Our prototypes have demonstrated safe performance from room temperatures to 140°C, albeit with reduced capacity at the top end of this range. Nail penetration tests both on freshly assembled and cycled pouch cells (0.5Ah capacity) did not result in any noticeable increase in temperature. Significantly, post mortem examination confirmed that there was no localized temperature increase at the point of puncture. This is due to the rapid spread of the reaction across the full surface of the Li electrode producing effective heat dissipation.

Intellectual Property

OXIS intellectual property portfolio is 22 patents granted and a further 47 pending. These protect the following key areas of the OXIS Technology:

1. Structure and composition of positive electrode
2. Electrolyte system
3. Battery design
4. Protection of Li electrode
5. Li-Sulphur electrochemistry