Polymer Lithium Battery

A polymer lithium battery is a newer type of battery that uses a plastic case and does not expand like liquid batteries. However, they are not as flexible or lightweight as their liquid counterparts.

They can offer up to 3.6 V, three times more than standard batteries, and have twice the energy density. Plus, they don’t have memory effect that causes the capacity to drop over time.

High Energy Density

As portable electronic devices have become indispensable in modern society, energy density has been the primary driving force for the development of lithium-ion batteries (LIBs). Compared with conventional Ni-Cd and Ni – MH LIBs, Li – polymer cells can achieve operational voltages of up to 3.6 V (three times higher) and energy densities of 120-150 Wh kg 1 (two to three times greater), providing a much more practical means of delivering high-power energy.

While achieving high power levels, the battery must also be safe and polymer lithium battery reliable, particularly in terms of the self-discharge level and the formation of lithium dendrites. This requires an electrolyte with a wide electrical conductivity window and good contact between the electrodes and the SSE.

Soft, flexible polymer-based SSEs can provide favorable contact with the electrodes. However, they tend to have narrow electrochemical stability windows and poor cathode wetting, thereby hindering the Li+ conduction in the anodes. Furthermore, they suffer from the formation of interfacial space-charge layers which further hamper the Li+ conduction.

To overcome these issues, a variety of advanced materials have been introduced to improve the fundamental properties of polymer-based SSEs. For example, gel-forming polymers such as poly(ethylene glycol) methyl ether acrylate (PEGMEA) and cycloaliphatic urethanes (CGPEs) offer improved mechanical strength and ionic conductivity via the addition of ion-conductive plasticizers. Moreover, the addition of ceramic fillers enables them to suppress the growth of lithium dendrites and to operate at elevated temperatures.

Long Cycle Life

Lithium polymer batteries usually have a much longer cycle life than their liquid lithium counterparts. However, actual battery lifespan depends on many factors such as environmental conditions (temperature, charge/discharge cycling, charging protocol), storage voltage and more.

In order to overcome this limitation, researchers developed gel and solid polymer electrolytes for all-solid-state LIBs that exhibit high ionic conductivity and chemical/electrochemical stability with lithium metal. In particular, a one-of-a-kind gel-like ionic conducting polymer with an electrolyte transference number of 0.67 was prepared by mixing poly(1,3-dioxolane) and lithium trifluorosilicate (LiTFSI).

The resulting gel polymer electrolyte (GPE) showed superior electrochemical performance in all-solid-state LIBs. In cyclic voltammetry (CV) measurements, the GPE exhibited two pairs of redox couples at 3.6/3.65 V and 3/3.2 V, similar to the redox couple observed in liquid LIBs. The GPE also exhibited a lower insertion/extraction current than liquid LiBs at the same scan rate.

Besides, the GPE electrolyte is stable against dendrite formation and shows no sign of degradation over 250 cycles. Furthermore, EIS measurements of the all-solid-state LIB showed negligible changes in electrolyte resistance Rhe, interfacial resistance Rif and charge transfer resistance Rct at different SOD/SOC.

Superior Safety Performance

With their dual function as separator and electrolyte, polymer lithium batteries offer a number of advantages over traditional liquid-based lithium ion batteries. As separators, they physically separate the positive and negative electrodes, preventing direct contact and potential short-circuits. As electrolytes, they facilitate the movement of ions, such as lithium ions, between the two electrodes during charging and discharging.

As for safety, the use of a solid rather than liquid electrolyte means that there is less of a risk of leaking batteries. This makes them much safer than their liquid-based counterparts, and more resistant to damage or puncture.

This advantage extends to their ability to withstand extreme environmental conditions. Unlike conventional LIB cells, which experience large temperature swings that can damage battery materials, SEB cells operate at a single constant operational temperature after a brief period of self-heating. This ensures minimal degradation of the battery materials even under high-voltage charging and operating temperatures.

In addition, SEB cell capacities and power densities are also superior to the baseline LIB battery. They can endure 1254 exposures to high-voltage abuse (constant current charge to 4.4 V, constant voltage at 40degC for 20 cycles) with a capacity retention of 80%, and they are up to 5x more stable and less prone to thermal runaway than the baseline LIB battery. Additionally, they generate less gas during high-voltage charges and exhibit significantly lower DCRs than the baseline LIB battery.

Minimal Dendrite Formation

Dendrite formation is a major challenge for LIBs as it directly leads to micro short circuits and battery failure. It is often unavoidable during fast charging and overcharging. Current LIB-based energy storage systems (BESS) utilize smoke, heat, and gas detection to provide early warnings. However, these methods are unable to accurately detect the very early stages of dendrite growth. Therefore, the development of a highly sensitive and reliable method for detecting micron-scale Li dendrites is urgently required.

SSBs are able to significantly reduce the risk of dendrites by employing nonflammable solid-state electrolytes and graphite anodes. Furthermore, they also employ a unique combination of high-voltage cathode materials, which allow for a higher theoretical specific capacity than conventional lithium metal batteries.

The key to preventing dendrites is to ensure the lithium concentration gradient across the electrode surface is not steep. This can be achieved by slow charging and Li-ion battery pack avoiding extremely cold conditions, as these both help to alleviate the strain on the anode and prevent the generation of a steep gradient.

The experimental results show that the CNM promotes regulated mass transport and suppresses the side reactions between Li and the carbon host, resulting in a flat voltage profile with low polarization over 300 cycles. Moreover, the EIS results confirm that the CNM allows for faster ion transportation. The pore size of the CNM is smaller than that of Celgard and enables ultra-low interfacial resistance.