Saft LSP lithium batteries - Which capacitor for your IoT application?
Capacitors store and release charges to sustain sudden voltage peaks. Combined with lithium batteries, they act as pulse helpers to quickly deliver the high power required by IoT devices. Many capacitors are now available in our LSP range: which hybrid battery solution should you chose to successfully energize your IoT project?
In April 2020, we launched a new range of products, the LSP20F range, to address the needs of a new generation of smart devices demanding a higher power pulse capability at a wider operating temperature range, for a longer lifetime. Our LSP range combines reliable, low self-discharge Li-SOCl2 cell technology and a state-of-the art and carefully selected LiC (Lithium-ion Capacitor) acting as a pulse helper. We have since enhanced the range with different capacitors, allowing us to answer most customers and telecommunication protocols’ specifications.
We asked Romain Cayzac, Technical Manager of the CE division in Poitiers, our R&D department, to explain the various options and capacitors now available to IoT developers in our LSP range.
Why did we create the LSP range?
“Saft is producing the LS range based on Lithium-Thionyl chloride (Li-SOCl2) chemistry, that is characterized by its high voltage and high specific energy. Their bobbin construction makes these cells particularly well suited for applications requiring very low continuous or moderate pulsed currents such as metering devices. With its remarkably low self-discharge, the LS range is designed to offer a long-lifetime (from five to 20+ years) for applications featuring a few µA base currents and periodic pulses.
For higher pulse solicitations, we have the LSH, also based on Lithium-Thionyl chloride, that features a spiral construction. This design optimizes the delivery of high current at the expense of the capacity (typical applications of 10 years). Our range therefore lacked a battery that could offer more than 10 years capacity for applications requiring high pulse current and a high voltage of 3.6V.
So we created the LSP range.
What exactly is the LSP range?
The LSP range brings together our low self-discharge Li-SOCl2 cell technology and a capacitor or pulse helper, that can either be an electrolytic capacitor, an electrochemical double layer capacitor, or a lithium capacitor.
Why do we need a capacitor acting as a pulse helper?
Li-SOCl2 cells are subject to passivation, a phenomenon that causes the formation of a Lithium Chloride layer on the anode.
Passivation protects the cell from self-discharge and enables their long shelf life. However, the passivation layer boosts the internal resistance of the cell, which can cause low voltage readings at initial times (few ms range) upon connection of a resistive load or current to the cell. This process is particularly common after storage in warm temperatures.
Of course, our LS range can deal with it, but some applications, with high current pulses and voltage cut-off, frequent “high” temperature excursions (above + 40°C), and for which any voltage recording below cut-off will trigger a "low battery" warning signal, have more chance to be disturbed by passivation.
To avoid this, we add a capacitor, a supercapacitor, or a lithium capacitor in parallel with the cell. The capacitor stores charges to help increase the necessary voltage and prevent any delay in current delivery. The amount of electric charge carried by the pulse helper at a given electric potential is called capacitance and is measured in farad (F).
What are the different capacitances available?
We have a wide range of capacitors to answer a variety of customers needs.
We first created the LSP 3F (3 farad) that features an electro-chemical double layer for water meters that need to transmit regularly at low temperature (-30°C to +60°C). But at high temperatures, the solution is limited due to the leak current of this technology (leading to a cell’s capacity loss).
After conducting market studies, we have realized that customers needed pulse helpers that have a higher capacitance in farads for connected objects that required regular communication and strong —but not too long—pulses. We therefore created the LSP 20F (20 farads), using a lithium capacitor, a solution that offers better stability at medium temperature (-20°C +70°C). We have tested it against competitors by accelerating the battery’s pulse solicitations and it shows better performance in terms of pulse capability, operating temperature range, and performance stability over its lifetime, as well as the lowest self-discharge and ESR (Equivalent Series Resistance) over temperatures.
Some customers also need a solution for applications with lower pulses at temperatures ranging from -60°C to + 85°C. They don’t want to burden their battery capacity with a bigger capacitor. So we created the LSP 20mF, using an electrolytic capacitor of 20 millifarads (20mF). The LSP 20mF is particularly useful for applications deployed in higher temperatures. It is also cheaper and offers an excellent price-value ratio. Saft is as of today the only manufacturer offering an electrolytic capacitor battery solution.
These 3 identified products, available in different cells sizes, from AA to D, have since been rolled out with several chains of capacitances, ranging from a few micro Farads (µF) to several tenths of a Farad. We are now able to offer stable and qualitative solutions that answer nearly all the needs of our clients. Some examples of applications of the LSP range: water gaz and heat meters, IOT sensors indoor and outdoor (smart parking, smart agriculture…), asset tracking…
Saft LSP - A flexible solution that can be customized to your needs
And for the unexpected, we can also develop customized solutions. If needed, we can use different capacitors or deport them, we can provide a plug and play solution using a connector or solder them, we can create cradles to receive the capacitor, assemble multiple cells in serial, or in parallel, etc.
A thoroughly tested solution for complete peace of mind
100% of our pulse helpers and 100% of our final LSP batteries are tested to ensure that they meet our standards in terms of pulse delivery once they are assembled. We only assemble the best components and perform several controls on our pulse helpers to ensure that they are in line with the customer's calculated lifetime. Some developers prefer to choose and assemble their own capacitor but don’t perform advanced testing on it, which might lead to disappointing results in the field.
With Saft’s LSP range, whatever the client desires, however complex the battery needs to be, we have a flexible and qualitative solution to meet their requirements.”
If you’d like to find out more about the LSP range of products or get personalized recommendation, get in touch with our application engineers at energizeiot@saftbatteries.com, they’ll be happy to help.
Characteristics of our LSP battery range
