The lithium-ion battery in your phone was patented in 1987 by Akira Yoshino — three years before anyone could buy one.

The intercalation design behind the rechargeable lithium-ion battery — a metal-oxide cathode and a carbon anode — was patented by Akira Yoshino and colleagues, filed in 1986 and issued in 1987, years before the battery reached store shelves.

The device powering the phone in your hand was on paper before you could buy it. US Patent 4,668,595, plainly titled "Secondary battery," was filed on May 9, 1986, and issued on May 26, 1987. Its lead inventor was Akira Yoshino, working with co-inventors Kenichi Sanechika and Takayuki Nakajima, and the patent was assigned to Asahi Kasei Kogyo Kabushiki Kaisha. The first commercial lithium-ion battery would not go on sale until 1991.

The patent claimed Japanese priority from 1985 — the year Yoshino built the design it describes. That gap between the idea and the product is the whole story of how a laboratory concept became the standard way the modern world stores energy.

How the patent actually works

The claim at the heart of 4,668,595 is deceptively simple: a nonaqueous secondary battery pairing a lithium-containing composite metal oxide cathode with an n-doped carbonaceous-material anode. In plainer terms, lithium ions shuttle back and forth between two hosts. When the battery charges, ions leave the metal-oxide cathode and lodge in the carbon; when it discharges, they move back, releasing current.

This shuttling is called intercalation — the ions slot into the layered structure of each electrode without destroying it. That is why the battery is rechargeable. Earlier attempts had used metallic lithium at the anode, which was energy-dense but prone to growing needle-like dendrites that could short the cell and, in the worst cases, catch fire. Yoshino's move was to abandon lithium metal for a carbon host that stored the ions safely.

According to the Nobel Prize committee, which awarded Yoshino a share of the 2019 Chemistry prize, the breakthrough came in 1985 when he developed a battery using a petroleum-coke carbon anode — the first commercially viable lithium-ion design. The prize citation credits that carbon anode as the piece that made the whole system practical rather than merely possible.

Why the 1987 date matters

The dates are the part people trip over, so it is worth being exact. Yoshino filed in Japan in 1985. The corresponding US application, number 06/861,423, was filed May 9, 1986. The patent issued on May 26, 1987. And Sony did not bring a lithium-ion battery to market until 1991. The intellectual property existed for years before the manufacturing, the safety testing, and the supply chains caught up.

That sequence is normal for foundational inventions, but it is easy to forget how much unglamorous work sits inside the gap. In a WIPO Magazine interview published in 2020, Yoshino described the underlying Japanese filing — Japanese Patent No. 1989293 — as covering a rechargeable cell built from a lithium-cobalt oxide cathode and a carbon-based anode. The cobalt-oxide cathode traces to separate work by John Goodenough, and the layered-compound insight to Stanley Whittingham; Yoshino's contribution was assembling a full, workable cell and proving it would not burn.

One concrete detail captures the difference between a patent and a product. Yoshino has recounted testing early cells by dropping heavy weights on them and setting them alight to see whether they would explode. A design that reads cleanly on a page still has to survive being punctured, overcharged, and left in a hot car. The patent describes the chemistry; the years afterward established that it was safe enough to sell.

What remains genuinely open is how much credit any single name deserves. The 2019 Nobel split the prize three ways — Whittingham, Goodenough, and Yoshino — precisely because the lithium-ion battery had no lone author. Yoshino's patent is the document where the pieces first came together in a manufacturable form, but the line between inventing a component and inventing the battery is one people still argue about, and the patent record alone does not settle it.