STEM与日常科技·英语30篇（6）
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Why Rechargeable Batteries Lose Capacity Over Time
可充电电池为何随时间推移逐渐失容
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Every time you charge and discharge a lithium-ion battery, microscopic changes occur inside its electrodes and electrolyte.
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During charging, lithium ions move from cathode to anode, embedding themselves into graphite layers—a process called intercalation.
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Repeated cycling causes some ions to get trapped or react with electrolyte, forming a solid-electrolyte interphase (SEI) layer.
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While a thin SEI protects the anode, thickening over time blocks ion pathways and raises internal resistance.
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Heat speeds up these side reactions, which is why storing batteries at 50% charge in cool places extends lifespan.
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Cathode materials also degrade: nickel-rich types offer high energy density but suffer faster structural fatigue.
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Manufacturers now use silicon blends in anodes to absorb more lithium—but swelling remains a key engineering challenge.
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Smart chargers limit voltage peaks and avoid full 100% charges unless needed, reducing stress on aging cells.
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Battery management systems track cycle count, voltage decay, and temperature history to estimate remaining health.
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Understanding this wear helps engineers design longer-lasting batteries for phones, EVs, and grid storage alike.