In an interview with The Post, Chen Bifeng, a marketing director for BTR, said the company serves about 75 percent of the market demand for natural graphite materials for batteries.

Occupying a central position in the graphite supply chain is BTR, the world’s largest supplier of natural graphite material for lithium-ion batteries, according to industry analysts. (Artificial or synthetic graphite is used in some lithium-ion batteries, but natural graphite, which is mined, is used predominantly. Natural graphite costs roughly half as much.)

To link the graphite in popular U.S. products back to factories in China, The Post used public records, company announcements and reports from industry analysts, as well as interviews with company officials at the Chinese International Battery Fair, a trade show in Shenzhen.

The other obstacle is that the people most knowledgeable about the sources of pollution, those who live near the factories, are often unwilling to complain publicly, especially in China.

Several companies declined to disclose the origin of their graphite. For example, Tesla, perhaps the best-known electric-car maker, uses Panasonic batteries. Tesla said those batteries have never included graphite from the Chinese company BTR, but it declined to identify its graphite source.

Tracing the origins of the graphite in a phone, for example, requires finding out where the ­phonemaker obtains batteries, where the battery makers acquire the portion of batteries known as anodes, and where the anode producers get their graphite. Moreover, because there are multiple suppliers at each step and various types of graphite, it is difficult to know where any given batch of the mineral ends up.

One obstacle is the complexity of supply chains and the secrecy that surrounds them.

Whether consumer companies are adhering to their environmental bona fides, however, is difficult to know, especially if the supply chain leads back to China.

For example, Samsung, in its “corporate sustainability report,” says that “we are especially committed to improving the quality of life for local residents as we pursue sustainable development that minimizes our environmental impact.” Apple and LG Chem have made similar claims.

The investigations arise after years of company promises that they were preventing pollution in their supply chains around the globe.

A spokesman for LG Chem, sister company to electronics giant LG, said it has been “monitoring our suppliers with extra interest” since the Chinese government brought up environmental issues relating to natural graphite production. It visited its Chinese supplier in 2014 and found no specific problems, the company said.

“Please be advised that Panasonic sent a fact-finding team to the site in question, they found evidence of pollution and the company is now taking immediate corrective action,” Mio Yamanaka, a Panasonic spokeswoman, said by email.

The Washington Post asked consumer-product companies and battery makers about their graphite supply chains. Here is what they said:

“We are currently investigating your concerns, so at this time we do not have detailed information,” said Yongdoo Shin, a spokesman for battery maker Samsung SDI.

In response to questions, some of the major electronics and car companies that sell products that rely on lithium-ion batteries said they were investigating the problems identified by Post reporting.

“Of course I would move if I had money!” Yu added, a trace of anger straining his face. “Who would want to live in this mai tai place? Here the dust is everywhere.”

The couple said they and others have complained to the local government but were told the graphite company is too big and beyond their power to contain. The company, they said, refused to meet with them and others in the affected area.

“We want to move, but we don’t have any money,” Zhang said.

“All the trees were fine until the graphite plant started,” Yu said. “It killed my trees.”

Yu Yuan, left, and Zhang Tuling stand in what is left of the couple’s tree orchard in the village of Jidong in Heilongjiang province. Zhang Tuling in her kitchen in Jidong in May. She and her husband say they think contamination of the air and the water from the nearby graphite plant killed their trees.

But it’s not just the air. The graphite plant discharges pollutants into local waters, Zhang and Yu said — a nightly event that they can detect by smell: The discharges leave a chemical odor that irritates their noses and throats. Those emissions have not only made their water undrinkable, they said, but also kept the local river from freezing in winter. They also think the discharge poisoned the poplar trees they were growing for lumber outside their home, just beyond their coops for ducks and geese and chickens.

They worry, too, about the health consequences, especially of breathing it in. Inhaling particulate matter can cause an array of health troubles, according to health experts, including heart attacks and respiratory ailments.

Since the graphite factory opened in Zhang’s village about five years ago, the graphite has become more than a nuisance. The couple live near Jixi, a city less than 50 miles from the Russian border. The dust has covered their corn crop, so much so that walking by a row of cornstalks leaves their faces blackened. And it seems impossible to keep it out of the house — at the dinner table, it often leaves them chewing the particles in their teeth.

Whatever the obstacles, the villagers who would talk offered remarkably consistent accounts of the pollution. The graphite, they typically said with disgust, makes everything mai tai , a regional expression meaning dirty.

In addition, plant managers and party officials sometimes sternly discouraged journalists from speaking with villagers. At three of the villages, the taxi carrying Post journalists was followed.

“Here he comes,” whispered one older woman in Mashan, near the city of Jixi in northeastern China, turning her back and pointing furtively at a village official who was approaching. She and her husband had been talking to a reporter about long-standing graphite pollution in her neighborhood. While some talked freely, there were people in all of the five areas with graphite plants who, like this couple, were reluctant to speak on the record.

Complaints about the pollution are often met with intimidation. People living near graphite plants frequently appeared fearful of pressing their grievances.

But the pollution continues. Villagers said the cleanup efforts failed — they were short-lived or otherwise inadequate — because local authorities are closely allied with company officials and unwilling to acknowledge the gravity of the environmental trouble.

Some provinces in China sought to crack down on the polluters, and three years ago they issued fines to several graphite companies.

Apple products use batteries made by those companies, too — specifically from Samsung SDI and LG Chem. But Fred Sainz, an Apple spokesman, said that for current products, the company has switched to synthetic graphite, which is not mined. The company declined to say when it made the change to rely exclusively on synthetic graphite.

After leaving these Chinese mines and refiners, much of the graphite is sold to Samsung SDI, LG Chem and Panasonic — the three largest manufacturers of lithium-ion batteries. Those companies supply batteries to major consumer companies such as Samsung, LG, General Motors and Toyota.

At five towns in two provinces of China, Washington Post journalists heard the same story from villagers living near graphite companies: sparkling night air, damaged crops, homes and belongings covered in soot, polluted drinking water — and government officials inclined to look the other way to benefit a major employer.

The world has grown reliant on lithium-ion batteries that power smartphones, laptops and electric cars. But the desperate search for the ingredients carries a steep cost.

The companies making those products promote the bright futuristic possibilities of the “clean” technology. But virtually all such batteries use graphite, and its cheap production in China, often under lax environmental controls, produces old-fashioned industrial pollution.

Smaller and more powerful than their predecessors, lithium batteries power smartphones and laptop computers and appear destined to become even more essential as companies make much larger ones to power electric cars.

A worker at the Jin Yang graphite factory in Mashan, in China’s northeastern Heilongjiang province, in May.

Zhang and Yu live near a factory that produces graphite, a glittery substance that, while best known for filling pencils, has become an indispensable resource in the new millennium. It is an ingredient in lithium-ion batteries.

“This is what we live with,” Zhang said, slowly waving an arm at the stumps.

Beside the family home is a plot that once grew saplings, but the trees died once the factory began operating, said Zhang’s husband, Yu Yuan.

By daylight, the particles are visible as a lustrous gray dust that settles on everything. It stunts the crops it blankets, begrimes laundry hung outside to dry and leaves grit on food. The village’s well water has become undrinkable, too.

“The air sparkles,” said Zhang Tuling, a farmer in a village in far northeastern China. “When any bit of light hits the particles, they shine.”

A t night, the pollution around the village has an otherworldly, almost fairy-tale quality.

Two of the plants, owned by Hensen Graphite and Haida Graphite, are in Shandong province, south of Beijing on the Yellow Sea.

Three of those plants are in Heilongjiang province in far northeastern China — two owned by Aoyu Graphite and one by BTR itself.

Each of the five Chinese graphite factories visited by Post journalists reported having provided graphite to BTR.

“Like everyone else, we sell some to BTR,” said Chen Geng, assistant to the president of Aoyu Graphite Group, which processes graphite at several locations in China. “They’re big.”

From BTR, the graphite is distributed around the world. The company sells graphite directly to the largest manufacturers of lithium-ion batteries, including Samsung SDI, LG Chem and Panasonic, according to Chen Bifeng, the BTR marketing director.

Those companies, in turn, make batteries for Samsung, LG, GM, Toyota and other consumer companies.

The Post sent letters to consumer companies whose battery suppliers have been supplied by BTR. The letters sought information on connections between the consumer companies and the natural graphite produced by Chinese firms blamed for pollution.

GM said a BTR subsidiary had been supplying graphite but declined to give further details. In a statement, the company said it “is committed to transforming the industry by reducing the environmental impact of our vehicles and manufacturing them in the most sustainable manner possible.”

A Toyota spokesman did not answer questions about its graphite sources but noted that the carmaker does not buy graphite directly and that “we make efforts to minimize the impact of our procurement activities on local communities. . . . We will ask our suppliers to take actions to avoid using certain materials if there is a concern about the source.”

BTR also has supplied graphite to Amperex Technology Ltd. (ATL), according to industry analysts, and ATL has made battery cells for Amazon Kindles, according to analysis by IHS, the global information company. Amazon.com was founded by Post owner Jeffrey P. Bezos. Amazon declined to answer questions regarding graphite sources but said in a statement: “We are committed to ensuring the highest standards in all areas of production and manufacturing. We work closely with our suppliers to ensure they meet our standards, and conduct a number of audits every year to ensure our manufacturing partners are in compliance with our policies.”

Representatives of BTR said that it seeks to ensure the graphite it uses has been mined and processed cleanly, a spokeswoman, Sally Guo, said by email from Shenzhen, and that it was “unfair” to blame the company for pollution.

All BTR subsidiaries are environmentally friendly and “qualified and approved from the government, and the production is strictly operated according to the related law and regulation,” she wrote.

She declined to offer specifics on BTR’s relationships with the plants in its supply chain.

While BTR provides the largest share of natural graphite for batteries, it is just one piece of a massive supply chain.

The graphite companies visited by The Post also supply other intermediate companies — not just BTR — and their graphite products are used in lithium-ion batteries around the globe. The graphite from those factories reaches some large Japanese companies, such as Nippon Carbon, as well as a Chinese company known as Shanshan that makes battery anodes.

The Post was unable to follow the graphite much further beyond those intermediate companies. Mitsubishi Chemical, Hitachi Chemical and Nippon Carbon did not respond to repeated requests for information about their customers. Shanshan officials hung up on a reporter.

Yu Zhen Jun says the yield from his corn crop has decreased as a result of the pollution from a nearby graphite factory owned by Aoyu. A ravaged hillside is all that remains of an abandoned graphite mine outside Mashan in May. Residents gather in the streets of Liumao, near a graphite mine and processing plant owned by BTR. A farmer heads home after working in the rice fields outside Liumao, near the city of Jixi in northeastern China.

‘City of Graphite’

Graphite is found around the world, but Heilongjiang province, a relatively remote locale on the Russian border, is the largest single source. For many there, it means big business.

At the entrance of Mashan, a small, dusty village near Jixi in Heilongjiang, four immense billboards celebrate the graphite industry.

Amid a jumble of storefronts, mopeds and pedestrians, the billboards depict samples of the gray powder against a backdrop of blue skies and daisies.

This, the sign says, is the “City of Graphite.”

China’s dominance in the graphite industry is in part because of price. While the mineral can be found elsewhere, the low cost of Chinese graphite discourages companies elsewhere from opening mines. The price of raw graphite suitable for refinement into anodes is about $550 per ton.

Stephen A. Riddle, president of U.S.-based Asbury Carbons, which began importing graphite from China in the 1970s, said the reason China was able to capture the largest share of the graphite market is mainly a matter of “price, purity and quantity.”

Chinese companies, Riddle said, benefited from a combination of low labor costs and determined ingenuity.

At one mine he visited in the early 1980s, for example, workers used picks and shovels to retrieve the raw material from the dirt — unlike the tractors and other heavy equipment used elsewhere — and then processed the graphite using handmade equipment.

“They were obviously a very low-cost operation,” Riddle said.

In the ’70s, China produced about a tenth of the world’s supply. By 2015, according to the U.S. Geological Survey, it was producing about two-thirds of the world’s supply.

The growth of the industry, particularly around Jixi, has had environmental consequences, especially in recent years.

Up a hill not far from the rice paddy worked by the villagers of Liumao stands a graphite mine and processing plant owned by BTR.

Several residents complained of the pollution, which they blamed for tainted water and dusty air.

“If you leave the window open, the graphite gets everywhere — on the furniture, on the plates,” Li Jie, 51, said as she cleaned some planters for rice seedlings. “It builds up on the windowsills. The dust covers the cherries we grow.”

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Zhao Guiyan, 63, also of Liumao, covers her nose when passing by some local waters, because of the chemical smell. “I’m worried what it’s doing to our health — breathing it in and eating it,” she said. Like many in the village, she relies in part on food grown in her yard or her neighbors’.

“I wash the vegetables over and over again,” Zhao said. “But [the graphite] is still there. It tastes and feels like you are chewing sand.”

In Mashan, residents reported similar problems. Mashan boasts several graphite plants, including another owned by BTR and one by Aoyu.

Lyu Shengwen, 55, a laborer, and his son share a two-bedroom home with a bathroom outside. They’ve been living in Mashan about 20 years, and around 2010 they noticed a rise in dust from nearby graphite plants.

“The dust . . . it’s everywhere,” Lyu said, grimacing.

He marched to a windowsill, swept his hand across it and then turned his blackened fingers toward visitors.

He shrugged and then headed outside toward a clothesline, from which he pulled a drying pair of pants and shook them. A cloud of dust appeared. Then, retrieving a black hose that supplies well water, he invited his guests to examine the water. It was cloudy and, he said, undrinkable — so oily that they now retrieve drinking water from a source more than a mile away.

“They mine anywhere on the mountain that they want to,” Lyu said of the graphite companies. “The plants release their discharge into the water. And it’s impossible to do anything about it.”

With Lyu now shouting, his neighbor Liu Fulan, 62, wandered by, curious. A farmworker, Liu lives with her son and 11-year-old granddaughter. A paper sign, pink and gold, hangs from Lyu’s front doorway. It asks for good fortune.

Liu nodded as Lyu expounded on the nuisance created by the graphite plant.

“You cannot survive without a bath every two days,” Liu said.

She apologized for the state of her home.

“I should clean — I used to clean,” she said sheepishly. “It’s mai tai. But I gave it up. I have too much to do already with the crops.”

Lyu Shengwen, 55, center, at his home in Mashan, says graphite pollution from the local factory is everywhere. “It’s impossible to do anything about it,” he said. Lyu Shengwen, 55, shakes graphite particles off his freshly washed clothes outside his home in Mashan.

In the air, in the water

Despite the name, only a small portion of a lithium-ion battery consists of lithium. Graphite is used to make the negative electrode and represents about 10 to 15 percent of the cost of a typical lithium-ion battery, according to analysts.

The demand for graphite has risen in parallel with the demand for more-powerful laptops, tablets and phones.

Ten years ago, for example, the battery of the best-selling Motorola Razr had a capacity of 680 milliamp-hours. Today, the batteries in the best-selling smartphones have three or four times that.

Video: How lithium-ion batteries work Lithium-ion batteries work much like other batteries — there’s a positive electrode and a negative electrode, and the electrons move from one end to another, creating a charge. The difference is the materials inside, which make them lighter, longer-lasting and rechargeable. Watch the video

Lyu Guoliang, senior engineer at the graphite business association in Jixi, said the demand for graphite rose very rapidly in 2010, driven by the demand for lithium-ion batteries.

Graphite for batteries must be refined to high levels of purity, and the flakes must be reformed into tiny spherical or potato-like particles. This extra refining means that the refined graphite is worth 10 times as much as the raw material, said Lyu, and that made the business particularly attractive.

But without proper controls, mining and refining can cause pollution in two ways — by air and by water.

Graphite powder can quickly become airborne dust, drifting for miles. Without systems of tarps and fans to keep it under control, the resulting fine-particle pollution can cause an array of breathing difficulties, such as aggravating lung disease or reducing lung function, and has been linked to heart attacks in people with heart disease, according to the U.S. Environmental Protection Agency.

Graphite operations can also lead to pollution because their chemicals leak into local waters. According to industry sources, the purifying process, especially in China, is commonly done with acids, often hydrofluoric acid, a highly toxic substance.

This method is cheaper than the one used in other countries, where the graphite is purified by “baking,” — that is, heating it up. Riddle, of Asbury Carbons, said refining graphite that way is better for the environment but adds about 15 percent to the price. He said that for the past 20 years his company has insisted on purchasing only graphite refined this way.

“We had hoped more companies and users would follow our lead, but this has not been the case,” Riddle said.

Tracing your battery’s graphite The lithium-ion battery industry has a massively complicated supply chain. Each consumer company has dealt with multiple suppliers — and their suppliers have dealt with multiple suppliers. This shows some of the connections within the industry. See companies' responses to Washington Post's investigation. MINING AND PROCESSING Aoyu Graphite Other sources Haida Hensen BTR Other anode makers ANODE MANUFACTURERS BTR BATTERY MANUFACTURERS Samsung SDI ATL LG Chem Panasonic Cathodes come from other manufacturers General Motors LG Toyota Amazon Samsung CONSUMER PRODUCT MAKERS They use the batteries in cellphones, laptops, tablets and electric vehicles. MINING/PROCESSING Haida Hensen Aoyu Graphite Other sources BTR ANODE MFG. Other anode makers BTR BATTERY MFG LG Chem Samsung SDI ATL Panasonic ELECTRONICS MFG General Motors Samsung Amazon Toyota LG BATTERY MANUFACTURERS They build batteries from cathodes, anodes and electrolyte solutions, all sourced from different companies. CONSUMER PRODUCT MAKERS MINING AND PROCESSING They use the batteries in cellphones, laptops, tablets and electric vehicles. Amazon Cathodes come from other manufacturers BTR ATL Samsung ANODE MANUFACTURERS Haida Samsung SDI LG BTR Aoyu Graphite LG Chem General Motors Hensen Other anode makers Panasonic Other sources Toyota Sources: Public documents, interviews with company officials and industry analysts.

‘War against pollution’

The Chinese government has shown increasing concern about the nation’s environmental woes.

After decades of extraordinary economic growth, the country’s air has become an acute health danger. A million or more Chinese die prematurely every year because of outdoor air pollution, according to multiple estimates, including the report known as the Global Burden of Disease, part of a project run out of the University of Washington. One of the critical groups of pollutants in the Chinese air is “particulate matter” — dust, soot, smoke — a category that includes the air pollutants emitted from graphite plants.

Meanwhile, water quality in China has deteriorated, too. In 2015, the portion of the country’s groundwater supplies classified as “bad” or “very bad” stood at over 60 percent, according to China Water Risk, a nonprofit group that tallies figures from China’s Ministry of Environmental Protection. More than a quarter of China’s key rivers were deemed by the government as “unfit for human contact,” according to the group.

According to a report on graphite mining shown on state-run CCTV, the rivers in Jixi show levels of lead and mercury that are many times the national limit. Given the array of industry in the area, however, it is impossible to say how much of the lead and mercury come from the graphite industry.

“We will resolutely declare war against pollution as we declared war against poverty,” Premier Li Keqiang announced in 2014.

About three years ago, the country’s environmental efforts focused on the graphite industry, and records indicate that more than a dozen companies were issued citations by provincial and city officials, mostly in Heilongjiang and Shandong provinces, where most of China’s graphite business is done.

For example, Aoyu, which operates the plants near Lyu Shengwen and Liu Fulan in Mashan, was cited for not controlling the dust and the water pollution. It was fined roughly $7,500 for those infractions and asked to make improvements, according to a database of government records kept by the Institute of Public and Environmental Affairs (IPE), a Beijing-based nonprofit.

Likewise, BTR faced similar enforcement efforts for air and water pollution.

So, too, has Hensen, a graphite producer in Shandong province that sells to BTR, according to its manager, who did not respond to emailed questions regarding the water pollution.

Guo, the BTR spokeswoman, said that the plant in question has been improved and won the approval of the local government. She attributed the complaints to the fact that BTR is an environmental leader within the industry. As a result, she said, “we think it is normal . . . that someone attacks BTR by improper means. . . . BTR will talk with local people. . . . We would like to prove to them that BTR doesn’t make pollution on the water and crops.”

More from this series Cobalt in Congo Workers, including children, labor in harsh and dangerous conditions to meet the world’s soaring demand for cobalt. Graphite in China There’s a trace of graphite in many of today’s consumer devices. In these Chinese villages, it’s in their water, inside their homes and on their food. Lithium in Argentina Indigenous people are left poor as tech world takes lithium from under their feet.

An Aoyu official hung up on a reporter seeking comment about the pollution.

But not all of the graphite factories appear to have been targeted by the crackdown. For two of the five factories visited by Post journalists, no records of any government citations could be found in the IPE database.

And even at those places where polluters were cited by the government, neighbors said that if any improvements were made, they were short-lived or not substantial enough to clean up the problem. Villagers said some factories employ pollution prevention measures — such as tarps to keep graphite from flying away, or actions to prevent toxic sewage from flowing into local waters — only when the environmental officials are present.

“It was worse last year, but it’s still bad,” Li Jie said in Liumao. “Everything is mai tai.”

The trouble, residents and some industry representatives said, is that while the government wants to protect the environment, they also want to protect the jobs at the graphite factories.

Hou Lin, 30, works at the Aoyu plant in Mashan as a safety manager. He walked by as some farmers were complaining to reporters about the pollution.

“The company pollutes a lot,” he agreed. “But people need to have jobs.”

Bags that are used to carry graphite on cargo trucks lie adjacent to a graphite factory in Mashan, China, in May. A worker from a graphite factory, his face covered with the mineral, makes his way home in Mashan, in the far northeastern province of Heilongjiang. A worker at the Jin Yang graphite factory in Mashan. A woman walks down a road in an agricultural section of Mashan. A sign near the entrance of the village touts Mashan as “the City of Graphite.”

Being watched

One of the main obstacles in clearing the pollution, villagers said, is the powerful alliance between local government officials and the owners of the graphite plants. The officials, the villagers said, protect the factories from environmental complaints.

At three of the five villages visited by Post journalists in May and June, a village official either tried to attend interviews or soon after inquired of the interviewees what had transpired in the interviews. Moreover, plant managers and party officials sometimes discouraged journalists from speaking with villagers.

After Post journalists visited the Haida Graphite plant in Pingdu, for example, a plant employee jumped in a car to follow their taxi off the property and through the village streets.

The taxi stopped twice in the village so The Post could interview more people. At each stop, the driver of the Haida car approached to within a few feet and blared the car horn continuously, making talking to villagers impossible. The driver relented only when The Post’s taxi left the area. Asked to comment later about the pollution complaints, a Haida official accused a Post reporter of “espionage” and refused to answer questions.

Similarly, after The Post visited a BTR graphite factory in Jixi, two cars with several men inside began following the reporters’ taxi. Three times, over several miles, the taxi pulled over to let them pass. Each time, the following cars pulled over and stopped behind the Post taxi. Confronted, the men in the cars told reporters that it was just a coincidence that they had stopped at the same time that the taxi did. The men said they were mapping out a bicycle race.

The intimidation has an effect on villagers.

Not far from the Hensen graphite plant in Laixi is a small factory that makes women’s underwear. Han Wenbing, 48, is the owner. A large man, proud of his workshop, he was eager to talk about the graphite pollution.

He readily invited reporters into his home, showing the dust quickly gathering on his kitchen table and showing how his well water, which had been fine for drinking, now is topped with a gray film.

But as he made his case against the graphite plant, his wife grew nervous — and then angry. To speak out would only cause trouble with the plant manager and village officials, she warned her husband.

“Yes, there is absolutely an impact [from the graphite], but we don’t want to be on TV,” she said. “This could offend the boss of the company, which could affect our lives. You [reporters] wash your hands and walk away, but we live here.”

Han nevertheless wanted to make his complaints known. Once his wife acquiesced, he offered to point out a field that showed some of the worst effects of the pollution. The field had been used by small farmers, he said, but industrial runoff had affected the soil so much that “not even the weeds can grow.”

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Less than a few minutes into the car trip to the polluted field, though, Han saw the plant manager’s car parked by the side of the road.

“They know it — they know I’m with you,” he said warily.

Moments later, someone representing the village party chief called his cellphone. Village officials had been tipped off that journalists were asking questions. What, the village officials wanted to know, was he doing and who was he with?

The call had an effect. Pointing out the field for reporters would cause too much trouble, Han said. He asked that The Post’s car stop and leave him on the curb to walk home. Even so, he was willing to talk on the record about how the pollution affected his home.

His extended family — parents, siblings and children — all live in the area, he said, and he felt a responsibility to speak out.

“We have lived here for many generations,” Han said. “If no one deals with it, it will keep damaging us.”

Demand ramps up

While U.S. consumers may seem uninvolved in — and untouched by — the Chinese pollution, the truth is more complicated.

The U.S. demand for cheap goods helps keep the Chinese factories going. More than a quarter of the emissions of two key pollutants in China — sulfur dioxide and nitrogen oxides — arose from the production of goods for export, according to research published in 2014 in the Proceedings of the National Academy of Sciences. The largest share of exports goes to the United States.

Moreover, the same researchers found that some of the pollution in China reaches the United States — the air pollution drifts across the ocean and raises ozone levels in the western part of the country, according to the study.

“Outsourcing production to China does not always relieve consumers in the United States . . . from the environmental impacts of air pollution,” according to the authors of the study, which was conducted by a consortium of scientists from China and the United States.

Now the rise of the electric-car industry promises a huge surge in the lithium-ion battery business.

Making batteries big enough to power cars will cause a daunting leap in demand. A laptop requires just a handful of the familiar, thin, cylindrical lithium-ion batteries known as “18650s.” A smartphone requires even less. But a typical electric car requires thousands of times the battery power.

Today, the best known “gigafactory” for electric-car batteries is the one being built by Tesla in the Nevada desert — a plant the company says will produce 500,000 electric-car batteries annually. But it’s just one of many. About a dozen other battery gigafactories are being planned around the world.

This is “not just a Tesla story,” said Simon Moores, managing director of Benchmark Mineral Intelligence, a firm that tracks demand and assesses prices for raw materials in the industry. “The demand is rising everywhere, especially in China.”

Children play on a street in the Chinese village of Liumao in May.

Todd C. Frankel and Yanan Wang in Washington and Xu Jing contributed to this report.