雅思阅读 20: The Battery That Runs on Humidity（靠湿度运行的电池）

改编自 NC State University（2026年7月）。雅思阅读 Section 3 难度，约 1050 词。 素材来源：https://ece.ncsu.edu/2026/researchers-create-moisture-driven-tech-that-powers-green-batteries-and-dissolves-spy-gear/

Reading Passage

A. Batteries typically store energy in chemicals deliberately sealed inside a casing. A new device developed at North Carolina State University takes the opposite approach: it stores no energy at all until it is exposed to ordinary atmospheric humidity, which it then converts into electrical current. The moisture-activated battery, or MAB, consists of a magnesium anode and a silver/silver-chloride cathode separated by a cellulose membrane loaded with lithium-chloride salts. In a dry state, the device is inert; when ambient air carries even modest moisture, the water vapour dissolves the salts, creates an electrolyte, and allows current to flow. "Our battery eliminates toxic and flammable electrolytes because it's essentially running on salt water," says Amay Bandodkar, the assistant professor who led the work. The insight behind the design is counterintuitive. Conventional batteries try hard to keep water out; this one invites it in, treating the ambient atmosphere not as a contaminant but as a co-reactant. That reversal is what allows the device to sit on a shelf for years and still work the moment it is opened.

B. The design has two distinct applications. The first is as a green, disposable power source for low-cost sensors and medical devices — applications where conventional batteries are over-engineered, expensive and environmentally wasteful. Because the device activates only when it encounters humidity, it can be stored indefinitely in dry packaging and switched on simply by being exposed to open air. The second application, which has attracted particular attention from military and intelligence researchers, is dissolvable electronics. The same cellulose membrane that serves as the electrolyte can, once the battery has served its purpose, be engineered to break down completely in water or moisture, leaving behind no electronic waste. This makes the device suitable for temporary sensors — environmental monitors deployed after a chemical spill, medical implants that dissolve after use, or surveillance equipment that must leave no trace. The combination of long dry storage and instant activation solves a practical problem that plagues disposable sensors: by the time a conventional battery is needed, its charge has often leaked away. A moisture-activated cell, sealed until deployment, loses nothing to age.

C. The chemistry is elegantly simple. Magnesium oxidises readily in the presence of water, releasing electrons that flow from the anode to the cathode through an external circuit. The lithium-chloride salt acts as an ionic bridge: dry salts do not conduct electricity, but once dissolved by atmospheric moisture they allow ions to move between the electrodes, completing the circuit. The amount of current produced is modest — enough to power a small sensor or a radio beacon for hours, not enough to run a phone or an electric car — but that is precisely the point. For the growing market of ultra-low-power electronics, where devices spend most of their lives in sleep mode and need only brief bursts of current, a battery that activates on contact with air is simpler, cheaper and safer than a conventional sealed cell. This is not chemistry that will ever run a laptop. Magnesium-air devices are deliberately built for the bottom of the electronics market — devices so small, so numerous and so disposable that engineering them for a decade of service makes little sense. In that niche, their limitations recede.

D. The device's limitations are intrinsic to its design. Because it depends on atmospheric moisture, its output is affected by humidity: in very dry environments it may produce little current, and in very humid conditions it activates prematurely. Its energy output is also low relative to lithium-ion chemistry, and the magnesium anode corrodes irreversibly once activated, so the battery cannot be recharged. The research team is working on formulations that remain stable at a wider range of humidities and on a magnesium anode that lasts longer before oxidising completely. But Bandodkar emphasises that the target market is not high-density storage; it is single-use, low-power applications where a conventional lithium coin cell is unnecessary, expensive and environmentally burdensome. A soil sensor buried for a week, a medical patch applied to the skin, an environmental monitor dropped from an aircraft — these are the devices that the moisture-activated battery is built for. The team reports that a single small device can run a low-power sensor for many hours on ordinary indoor humidity, and that adjusting the salt loading lets them tune how quickly it activates and how long it lasts. Trade-offs remain, but the design variables are few enough that iterative improvement should be rapid.

E. The broader context is the explosion of "Internet of Things" sensors, which are projected to number in the tens of billions worldwide. Most of these devices currently run on coin-cell batteries that contain toxic metals and are rarely recycled. A battery that activates on contact with air, runs on salt water, and dissolves after use could substantially reduce the electronic waste stream. The dissolvability feature also opens applications that conventional batteries cannot serve: environmental sensors that must not contaminate the sites they monitor, medical devices that should not require surgical removal, and — the application that has drawn the most speculative commentary — surveillance equipment that vanishes without a trace. The technology is not a replacement for lithium-ion; it is a complementary solution for a niche that the battery industry has largely ignored. Sometimes, the best battery is the one you never have to throw away. Whether the technology moves beyond the laboratory will depend on manufacturing costs and on whether regulators accept dissolvable devices that vanish in the very environments where they are deployed. Early interest from both civilian and defence sponsors suggests the niche is real. The idea that a battery could be made to disappear on purpose is, in its quiet way, as radical as the first sealed cell was a century ago.

Questions 1-4

Choose the correct heading for paragraphs B, C, D and E from the list of headings below.

List of Headings i. How the device generates current ii. What the battery is designed to do — and not do iii. Two very different use cases iv. The environmental problem of billions of IoT sensors v. How magnesium is mined vi. The military history of espionage vii. The chemistry of lithium-ion batteries

1. Paragraph B: ____
2. Paragraph C: ____
3. Paragraph D: ____
4. Paragraph E: ____

Questions 5-8

Choose the correct letter, A, B, C or D.

5. What activates the moisture-activated battery? A. An external charging cable. B. Water vapour from the air dissolving salts in the membrane. C. Direct sunlight. D. A mechanical switch.

6. Why is the device considered safe? A. It contains no flammable or toxic electrolyte — essentially salt water. B. It uses no metals at all. C. It cannot be turned off once activated. D. It produces no electrical current.

7. What is a limitation of the battery? A. It cannot be used in humid environments. B. Its output depends on humidity and it cannot be recharged. C. It requires rare-earth metals. D. It only works below freezing.

8. What market is the device primarily intended for? A. Electric vehicles. B. Single-use, low-power sensors and dissolvable electronics. C. Grid-scale energy storage. D. Smartphones and laptops.

Questions 9-13

Do the following statements agree with the claims of the writer?

Write:

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

9. The battery uses a magnesium anode and a silver/silver-chloride cathode.
10. The battery can be recharged repeatedly.
11. The device can be stored indefinitely in dry packaging.
12. The research team is based in California.
13. Billions of IoT sensors currently run on rechargeable lithium batteries.

Questions 14-15

Complete the summary below using NO MORE THAN TWO WORDS from the passage.

The battery activates when atmospheric (14) __________ dissolves the salts in its membrane. It is designed for single-use, (15) __________-power applications rather than electric vehicles.

答案与解析

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