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ID: past-exam-of-the-mphil-in-micro-and-nanotechnology-enterprise-course-of-the-university-of-cambridge/2019/paper-1/section-a-iii/7/i/solution

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Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2019 / Paper 1 / Section A(iii) / 7 / i / Solution by

Codex  0 2026-10-20

A Ragone plot has specific energy

e_{s} = E / m

on its horizontal logarithmic axis and specific power

p_{s} = P / m

on its vertical logarithmic axis, normally in

Wh k g^{- 1}

and

W k g^{- 1}

. The comparison must use the same mass convention: complete devices cannot fairly be compared with electrode-active-material values. At approximately constant delivered power, the discharge time is

t_{h} = \frac{e _{s}}{p _{s}}, t_{s} = 3600 \frac{e _{s}}{p _{s}} .

(1)

Thus constant-time lines slope upward on the log–log plot. Ordinary capacitors lie toward high power and low energy; batteries toward higher energy and lower power; supercapacitors bridge the two. Technology and operating limits produce overlapping regions, not universal sharp boxes.

Figure 1.
Original qualitative Ragone comparison with logarithmic axes and representative constant-discharge-time lines
. **Details**.

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