A selected letter in The Guardian talking about electric vehicles claims:
The rare metals in lithium batteries are produced only in inconvenient places. More than 85% of the world’s supply comes from China. How dependent will that make us upon them?
What metals might it be talking about (no details in there) and is it confirmed from other sources? Bonus question: are these rare metals essential for making lithium batteries or just convenient?
Michael Karnerfors has provided evidence that China produces 95% of the world's rare earth elements. However, China does not hold that much of the world's reserves of such metals.
The US Geological Survey mineral commodity summary for 2017 for rare earths gives China's 2016 rare earth's production at 105,000 tons of a world total production of 126,000 tons; 83% of the world total.
However, China's known reserves are given as 44,000,000 tons, out of a total of 120,000,000; 37%. Other nations with a large portion of world reserves include Brazil (18%), Vietnam (18%) and Russia (15%).
To answer the question in the title, China does control roughly 85% of the current supply, but they don't control nearly that much of the potential supply. Were China to raise prices, it would simply allow mines in other regions of the world to be economical. This has in fact happened in the past, if I may be allowed to steal a link from matt_black's comment.
So while literally true that China controls the supply of 85%, they cannot leverage this position to any economic advantage. To answer the question in the quote from the OP, we (all the non-Chinese) are not dependent on them.
When the letter says...
The rare metals [...]. More than 85% of the world’s supply comes from China
...I believe the author means Rare-earth Elements/Rare-earth Metals.
REMs are necessary elements in the production of electronics, computer chips of all kinds, computer/phone displays, solar panels and a whole range of other products of that sort. This means that presently our modern society is entirely dependent on REMs to supply us with not only consumer products but also monitoring and control equipment for critical societal functions such as clean water, heat, sewage, energy production and distribution, food production and distribution, military hardware, and finance and banking.
As the Wikipedia article above states, China does indeed hold the overwhelming majority of the world's production of REMs. In 2010, China suppled 95% of the world's market for REMs.
The final point the letter makes is:
Mining these materials is far from environmentally friendly.
Is this true?
Yes, it seems so: http://www.bbc.com/future/story/20150402-the-worst-place-on-earth
95% of the Production comes from China... does that mean that 95% of the world supply is actually IN China and only available from China? Or that they are simply the only ones that can afford to mine those at a given price point (IE: Subsidized, without environmental protections, no worker protections, etc)?
Based on an CNBC piece with similar claims, the Guardian letter seems to be talking about cobalt:
For example, China controls 80 percent of the market in chemical cobalt, a crucial ingredient in lithium-ion batteries, [Benchmark Mineral Intelligence analyst Caspar Rawles] he said.
Oddly enough a techcruch piece is somewhat contradictory
Approximately 97 percent of the world’s supply of cobalt comes as a by-product of nickel or copper (mostly out of Africa).
Digging the Benchmark report that all seem to using for this data, it clarifies that the Chinese control is by their acquisition of African mines, in DRC in particular:
In 2015, the last full year of production, 102,000 tonnes of cobalt (all forms) of which 59% was mined from the Democratic Republic of Congo (DRC) as a by-product of copper production. Outside of the DRC, there are no significant production hubs with the second largest producer, Canada, accounting for 9% of total supply. Other producers include Russia, Cuba, Australia and the Philippines. In total, cobalt is mined in 14 countries.
China Molybdenum has made recent moves to secure long term supply for its domestic battery industry by acquiring Freeport McMoran’s Teneke mine in DRC for $2.65bn and with it 20,000 tonnes of additional cobalt capacity. The move puts China to the number one spot for countries that control the most cobalt supply, leapfrogging both Canada and Switzerland.
But it's still nebulous how 59% became 80% (or 85%).
As noted in the other answers, there's probably a confusion in some sources between "rare minerals" and (IUPAC) "rare earth" metals. Cobalt has been called the former (i.e. "rare mineral") in another Guardian piece, an article headlined by its staff this time.
So what about lithium batteries and rare earths? There's an article in The Bulletin of Atomic Scientists that probably clarifies much of the confusion(s). Basically lanthanum (a rare earth) was used is some old batteries:
Even in 2015, China accounted for more than 80 percent of global rare-earth production but also for about 70 percent of rare-earth demand—not an unreasonable balance. [...]
Some hybrid cars, like my 2001 Honda Insight, used nickel-metal-hydride batteries containing lanthanum [a rare earth], but those are now largely replaced by lighter lithium batteries, which typically use no lanthanum. (Both kinds of batteries are also recyclable, and infrastructure for recycling is emerging.) Tesla’s market-leading lithium batteries, like its motors, use no rare earths at all. Non-lithium batteries and potent potential substitutes for batteries (notably graphene ultracapacitors) are also emerging. [...]
Some writers claim that lithium, a light metal occasionally confused with rare earths by novices, is too scarce to support a big electric-car industry—a surprise to firms with vast lithium deposits in diverse countries.
This article does not specifically say that cobalt can be confused for a rare earth, but since lithium can... Furthermore, a blog on the site of the Union of Concerned Scientists says that the confusion can include cobalt:
Specifically, the use of lithium, cobalt, nickel, and other metals that are part of an EV lithium-ion battery pack has raised red flags about the poor human rights and worker protection records in the countries where these materials are mined.
A lot of these warnings have been incorrectly categorized under “EVs and rare earth metals.” Though neither lithium nor cobalt are rare earth metals, and rare earth metals aren’t nearly as rare as precious metals like gold, platinum, and palladium, there are important issues surrounding the production of lithium-ion batteries that must be acknowledged and addressed.
And if you need more proof that the confusion is likely, an article in The (Toronto) Star calls cobalt a "rare metal".
As you can read in this article, the main metals used in the common design of Li-ion battery are Lithium and Cobalt; lithium is quite abundant, but cobalt is a bit harder to find. It is usually produced as a by-product of nickel mining, and the main source has been the DRC (Congo); there, the use of child "labor" has been getting significant public exposure, and in response a number of large users of battery technology (Apple, Tesla) are seeking more responsible ways of sourcing (including recycling). There are also other technologies being developed (using Nickel, Manganese, Titanium) that do not rely on cobalt.
According to the cobalt institute, China "mines or refines" 45k tonnes of cobalt per year, out of a global production of about 94k tonnes. Interestingly, while the article states the DRC is responsible for 55% of the world production of cobalt, their table suggests that the DRC is not a major source of refined cobalt (400 tonnes) - probably because the ore is sent to other countries (China) for refining.
Note that there are other rare earth metals used in the manufacture of medical equipment, electronics and magnets (examples include neodymium, dysprosium, lutetium, ...) that are almost exclusively mined in China. This means that China does have a significant lever to enable (or throttle) the adaptation of advanced technology.
So while China certainly has positioned itself as a key source for strategically important materials, I would say that the claim in the letter is "doubtful".
Some of the answers are referring to "rare earth" elements. There is nothing in the claim or lithium ion batteries related to rare earth elements.
Lithium is the only metal ubiquitous to lithium ion batteries.
China produced 2000/35,000 or 6% according the 2017 USGS report on lithium.
Many lithium ion batteries also contain cobalt.
China produced 7,700/123,000 or 6% according to the 2017 USGS report on cobalt
