Technology · Overview

The backup cell trade-off, quantified

Every ride-through design starts with one cell choice: an LIC hybrid supercapacitor, a symmetric EDLC, or a Li-ion battery. The three overlap far less than headline slides suggest — one answers a load step in 1–50 ms, one stores ten times more energy per kilogram, and one carries a failure mode the other two do not have. This hub lays the trade-offs out in datasheet-class numbers before you commit a string count.

CapStack builds modules on the LIC side of that table — laser-welded, ±5% capacity-sorted, test-reported — because the millisecond tier is where rack power actually lives.

Deep-dive: LIC vs EDLC vs Li-ion

Three chemistries

One decision, three very different cells

LIC hybrid supercapacitor

3.8 / 4.0 V cell — about 30% fewer cells per string than a 2.7 V EDLC at the same bus voltage.

13.7–62 Wh/kg — roughly 10× the energy of a same-size EDLC.

500k+ cycle class in a 3.5→2.5 V window; −40 °C capable by series.

No thermal runaway — physical adsorption plus a prelithiated carbon electrode.

EDLC — symmetric double-layer

2.7–3.0 V cell — the classic double-layer workhorse, mature and widely second-sourced.

3–8.5 Wh/kg, 22–28 kW/kg — a pure power play with little energy reserve.

500k–1M cycles at 25 °C — the cycle-life benchmark.

Higher self-discharge and more cells per string at a given bus voltage.

Li-ion battery

~130–265 Wh/kg — the energy density king for hours-class storage.

1,000–5,000 cycles — high-cycling backup duty consumes the budget fast.

Thermal runaway risk — BMS interlocks and clearance are mandatory design inputs.

Cold limit — charging restricted below 0 °C; −20 °C is a working floor.

Head to head

Ten parameters, datasheet-class numbers

Conditions define every number below — cycle life in particular is always quoted against a voltage window and a temperature. Treat this as the shortlist; the deep-dive page expands it to 14 rows with the measurement conditions spelled out.

Parameter	LIC	EDLC	Li-ion battery
Cell rated voltage	3.8 / 4.0 V	2.7–3.0 V	3.2–3.7 V
Cells per string, same bus voltage	Baseline	≈30% more cells	Comparable count, shrinking with wear
Energy density	13.7–62 Wh/kg	3–8.5 Wh/kg	~130–265 Wh/kg
Power density	Up to ~22 kW/kg	22–28 kW/kg	0.5–3 kW/kg
Cycle life	500k @3.5→2.5 V / 50k @4.0→2.5 V	500k–1M @25 °C	1,000–5,000
Operating temperature	−40…+70 °C by series	−40…+85 °C	−20…+60 °C
Response to a load step	1–50 ms	Milliseconds-class	Electrochemical delay
Failure mode	No thermal runaway	No thermal runaway	Thermal runaway risk
Self-discharge	≥3.7 V held after 72 h rest	Higher, days-scale droop	Low
Cost position	Mid: above EDLC per farad, far below Li-ion per delivered cycle	Lowest per farad	Highest per delivered cycle in high-cycling duty