Lithium-ion（锂离子）batteries are the current front-runners for storing renewable energy, but their components can be expensive. Zinc（锌）batteries are easier on the wallet and the planet, but lab experiments are now pointing to ways around their primary drawback：They can’t be recharged over and over for decades.

The need for grid-scale（电网规模的）battery storage is growing as increasing amounts of solar, wind, and other renewable energy come online. This year, America is committed to making the American electricity grid carbon-free by 2035. To even out dips in supply, much of that renewable power will have to be stored for hours or days, and then fed back into the grid. For California alone, it wants to deploy（部署）more than 8800 megawatts of rechargeable batteries by 2026, and last week, the governor of California proposed $350 million in state funding to develop long-duration energy storage technologies. “That trend will not go down. It will only continue to grow,” says Mark Baggio, vice president for business development at Zinc8 Energy Solutions, a zinc battery producer.

“For power storage, Lithium-ion is the 800-pound gorilla,” says Michael Burz, CEO of EnZinc, a zinc battery startup, “but lithium, a relatively rare metal that’s only mined in a handful of countries, is too scarce and expensive to back up the world’s grids. We need an alternative to lithium. Zinc batteries may be one of the options.”

Non-rechargeable zinc batteries have been on the market for decades. More recently, some zinc rechargeable batteries have also been commercialized, but they tend to have limited energy storage capacity. Another technology, zinc flow cell batteries, is also making big steps. But it requires more complex pumps and tanks to operate.

So, researchers are now working to improve other varieties including zinc-air cells. They say although it’s urgent, there is a long way to go before they find a solution.

Every weekday, shortly after 11 a.m., a line forms at the Broadway and 38th Street location of Sweetgreen, the eco-conscious salad chain. By noon, the line has usually tripled （三倍）in size.

The scene is similar at the Chop't, or the Dig Inn, or the Just Salad one block south. Greens, once so unattractive that parents all over the country had to beg their children to eat them, have never been hotter.

At Sweetgreen , the appeal is partly ethical . The ingredients are sustainably farmed, sourced from trusted partner and served with transparency. There are vegetarian, gluten-free and “warm bowl” options. There are raw beets and organic carrots. It's enough to make the most wasteful among us feel satisfied . It is any wonder that Sweetgreen is the fastest growing salad chain in the United States?

The moral overtones extend even to the trash. As customers pay and head back toward their various workplaces , they pass an often Overflowing garbage bin with a proud sign above it that says that all of the company’s utensils, napkins, bowls and cups are plant-based, "which means     they go in the compost bin（堆肥箱），along with any leftover food." "Nothing from inside Sweetgreen goes to the landfill（垃圾填埋）,” the sign declares further, virtuously.

But that's far from the truth, although it,s not the chain's fault.

Zara Watson, a lawyer who eats at Sweetgreen three times a week, throws the waste from her healthful lunch directly in the trash because she does not have to compost at her office. So does Sam Hockley, the managing director at the software company Meltwater, who is willing to eat a Sweetgreen bowl for breakfast, lunch or dinner.

Salad is appealing not only because the food is healthy for us but because it's healthy for the world. But even as Sweetgreen and its marvelous effort, the compostable（可降解的） containers the chain puts such care into providing are, more often than not, going to a landfill.

Eric Goldstein, the New York City environment director, said that it typically takes a city about a decade to transition to successful composting. Now New York faces several challenges, one " which is educating people on how to compost in the first place. u!f you were to stop a person in the street, 1 don't know how many people could even tell you what composting really is," he said. "We need a large-scale program to let New Yorkers know why this is important and how to participate in the program .”

And of course, composting itself is not the gold standard of eco-conscious lunch disposal, “it's still best to use reusable things, even before composting and recycling,” Mr. Goldstein said. "But composting is an extremely valuable thing to do."

Love the way you walk

If listening to the footsteps in your home, you are likely to figure out who is walking around. The features which are most commonly used to identify people are faces, voices and fingerprints. But the way they walk is also a giveaway (使真相泄露的事物).

Researchers have used video cameras and computers to analyze people’s gaits (步态), and are now quite good at it. But translating such knowledge into a practical identification system can be tricky. Cameras are often visible, are difficult to set up, require good lighting and may have their view blocked (选档) by other people. A team led by Dr. Ozanyan and Dr. Scully have been looking for a better way to recognize gaits. Their answer: pressure-sensitive mats (垫子).

Such mats are nothing new. They have been part of security systems. But Ozanyan and Scully use a complex version of mats that can record the amount of pressure applied in different places as someone walks across it. These measurements form a pattern unique to the walker. The researchers turned to an artificial-intelligence system to recognize such patterns, and it seemed to work. One application of the mat-based gait-recognition system might be in health care, particularly for the elderly. A mat placed in a nursing home or an old person’s own residence could monitor changes in an individual’s gait that indicates certain illnesses. That would provide early waring of someone being at greater risk of falling over.

Perhaps the most interesting use of the mats, though, would be in public places, such as airports. For that to work, the footsteps of those to be recognized would need to have been stored in a database, which would be harder to arrange than the collection of photographs and fingerprints that existing airport security systems rely on. Many aircrew or preregistered frequent flyers would welcome anything that speeded up one of the most tiresome parts of modern travel.