The trauma faced by consumers and the pain of the Galaxy Note7 recall that Samsung Electronics is going through is unfortunate. The reported incidents of flaming devices highlight both the persistent need for portable energy storage and the problems with our dependence on chemical lithium ion batteries.
While portable, high-energy density lithium batteries have been a boon for mobile computing and pervasive sensors in many useful areas in our lives, they continue to be a bane for several undesirable characteristics: long recharge times, which leads to battery anxiety and constant hunting for recharge sockets; low cycle life, which leads to increased burden on landfill waste management; and the unsafe and environmentally unfriendly nature of the chemistry. All of these nagging issues make chemical, rechargeable battery cells troubling and downright dangerous to use, especially when you consider the vast number of these chemical energy storage cells in everything around us.
I am writing this open letter to highlight alternatives to chemical batteries that address these problems. We owe it to ourselves to seek to improve our lives and the planet by considering other options.
Lithium ion batteries are, by and large, safe as demonstrated by the millions of devices using them over the years. However, since active chemistry is taking place in these cells, the risk of runaway thermal breakdown is never completely removed. Instead of waiting for promises of a safe lithium-ion battery technology, which may be too expensive or too far out in the future, a new generation of higher energy hybrid-supercapacitors offers a choice available today.
There are certainly other chemical energy storage alternatives that are safer than lithium ion — like zinc-based electrochemical storage batteries — and these should also be considered. Nickel metal Hydride (NiMH) batteries and Nickel Cadmium have also been used for a long time; Table 1 compares these chemistries and their properties.
Table 1. Comparison of chemical energy storage alternatives
(Click Here to see a larger image. Source: Shreefal Mehta)
However, these electrochemistries also share some of the previously noted undesirable characteristics associated with chemical forms of energy storage. Thus, the benefits of new high-energy supercapacitors are worth considering in light of their improved performance and form factors that were not available until recently.
Supercapacitors store electrical energy without any chemical reactions and hence will not develop internal thermal runaway chemistry or internal shorts leading to fires. The Achilles heel of standard supercapacitors has been a very low capacity to store energy per volume and a rapid rate of self-discharge (low charge retention once charged) compared to lithium ion and other rechargeable batteries. These limitations, including a bulky form factor in metal cylinders, have restricted the use of supercapacitors to very specialized applications… until now.
New developments and advances in hybrid supercapacitors technology have addressed these two main issues, making it more suitable for a wider range of applications.
Commercially available hybrid supercapacitors have various chemistries (using metal oxides such as manganese, ruthenium, lithium-ion to increase electrode voltage and thus energy density) and have demonstrated as much as 10X energy density as compared to previous generation supercapacitors. Most importantly, these new advanced hybrid supercapacitors also have significantly improved charge retention, with some having very low self discharge similar to lithium-ion batteries. These high energy supercapacitors are also available with thin, prismatic form factors similar to lithium-ion battery pouch cells, and these new characteristics are enabling hybrid supercapacitors to power many new applications for the first time.
Table 2. Comparison of lithium ion batteries, traditional symmetric EDLC Supercapacitors, and hybrid asymmetric supercapacitor or lithium ion capacitor (Click Here to see a larger image. Source: Shreefal Mehta [Note: the values for the hybrid supercap are taken from the PowerResponder PBC product line])
As shown in Table 2, higher-energy hybrid supercapacitors (e.g., lithium-ion capacitors or LICs) still have 10X lower energy capacity per volume than a lithium ion battery, but they also have a voltage range that is an easy “drop in” replacement for lithium-ion circuits, thereby making them worth considering as a selective replacement (even an after-market product) in certain consumer or industrial products based on usage patterns and safety needs.
Specifically, high energy supercapacitors are a good fit for applications where a two-to-three–minute recharge of the energy storage cell can get the product ready for a few hours of use. The concept of “Energy Snacking” — fully recharging in minutes several times through the day — also makes the long cycle life of supercapacitors (tens of thousands of cycles) a good fit for this type of product usage. An always-available product (with a few minutes of recharge time) is preferable to one where duplicate lithium-ion charge packs have to be purchased and discarded into landfills as they fade in capacity. This rapid recharge capability to then store enough energy for short time functionality is a good fit for many of today's portable electronic products and mobile lifestyles.
A good example of the need for safe, long cycle life, handheld power is in industrial settings such as handheld credit card readers carried by flight attendants in airlines world-wide. A hybrid supercapacitor can provide enough run time for the few hours of typical intermittent usage and can be recharged in minutes if needed again, thereby avoiding the necessity to carry multiple extra charge packs and alleviating safety concerns in this sensitive environment.
Product manufacturers and consumers need to know that a safer alternative to lithium ion is available today for specific applications where consumer safety is a high concern.
Shreefal Mehta is CEO of The Paper Battery Company. He invites readers to explore alternative energy storage options, especially those from The Paper Battery Company, which (he notes) has a UL-certified product currently in volume manufacturing.