Source: Tesla's Open House - Batteries - Motor Trend
"Three battery packs are being produced, for the Roadster, the Smart EV, and the upcoming Mercedes-Benz A-Class EV for Europe -- a pack that possesses what's currently the highest battery energy density in world. And speaking of records, production of the Roadster's motor (which has the world's highest power density) is gradually being transferred to Palo Alto from its various subcontractors.
But the downstairs battery lab is the facility's most compelling visit. It's a catacomb of mad scientists, Tesla-made dynamometers (with Roadster motors flipped into acting as generators), a power substation equal to a sizable portion of Palo Alto's power, and a destructive testing lab with shaker tables and a mammoth loudspeaker to acoustically rattle batteries packs to bits. Most interesting of all, though, is the sheer volume of data they're acquiring on those 18650 cells.
Produced by several competing suppliers, the bundling of barrel loads of 18650's has become an article of faith for Tesla. Unlike Nissan's Leaf and Chevy's Volt, which use far fewer, large-format lithium-ion cells, Tesla is adamant that it is right -- and those other guys are wrong. "Runaway thermal events" are a genuine worry.
Tesla's view is that cell "events" are unavoidable. No production process, it contends, is perfect enough to completely avoid them. However, each 18650 cell is so individually small (a little bigger than a AA battery) that individual failures aren't catastrophes; they may not even be noticed. More than a billion of these cells are produced each year, meaning the manufacturing process is extremely mature -- including lots of hard-learned internal safety features. The day of our visit, Tesla's Roadster fleet turned its seven-millionth-mile in the field, and data from each car's battery (containing 66 thermal sensors monitoring the pack's nearly 7000 cells) is downloaded, amassed, and analyzed at every service. Tesla's data trove is now so sizable, that sharing insights with its Japanese, Chinese and South Korean cell suppliers is a significant negotiating tool. (By the way, these cells are also now being created specifically for EVs, leaving their laptop origins behind; they're also seeing year-over-year price drops of 6-8 percent). During his presentation later in the day, Kurt Kelty, director of Battery Technology, challenged we journalists to ask-the next time we attend another manufacturer's EV introduction -- exactly what safety precautions they've taken to prevent a runaway thermal event. His expression suggested they don't really have an answer.
This most obvious influence of this safety drumbeat is how the Model S's battery lays like a slab at the bottom of the chassis, benefitting packaging, underbody aerodynamics, and center of gravity issues. Appearing to be about the size of a 4 x 8 sheet of plywood and roughly 4 1/2 inches thick (with the corners scalloped off), the battery's structural encasement, all by itself, offers more torsional rigidity than the Roadster's entire chassis. Internal structures should make it robust enough to satisfy the government's upcoming side pole impact standards, yet it might be removable in about a minute. When asked if this suggests a collaboration with Better Life (proponents of fast-swappable batteries) the answer was no -- but you have to wonder what the purpose of it is, then. The battery enclosure will also be employed as a stiff basis for the Model S's steering rack."
:takeit:
"Three battery packs are being produced, for the Roadster, the Smart EV, and the upcoming Mercedes-Benz A-Class EV for Europe -- a pack that possesses what's currently the highest battery energy density in world. And speaking of records, production of the Roadster's motor (which has the world's highest power density) is gradually being transferred to Palo Alto from its various subcontractors.
But the downstairs battery lab is the facility's most compelling visit. It's a catacomb of mad scientists, Tesla-made dynamometers (with Roadster motors flipped into acting as generators), a power substation equal to a sizable portion of Palo Alto's power, and a destructive testing lab with shaker tables and a mammoth loudspeaker to acoustically rattle batteries packs to bits. Most interesting of all, though, is the sheer volume of data they're acquiring on those 18650 cells.
Produced by several competing suppliers, the bundling of barrel loads of 18650's has become an article of faith for Tesla. Unlike Nissan's Leaf and Chevy's Volt, which use far fewer, large-format lithium-ion cells, Tesla is adamant that it is right -- and those other guys are wrong. "Runaway thermal events" are a genuine worry.
Tesla's view is that cell "events" are unavoidable. No production process, it contends, is perfect enough to completely avoid them. However, each 18650 cell is so individually small (a little bigger than a AA battery) that individual failures aren't catastrophes; they may not even be noticed. More than a billion of these cells are produced each year, meaning the manufacturing process is extremely mature -- including lots of hard-learned internal safety features. The day of our visit, Tesla's Roadster fleet turned its seven-millionth-mile in the field, and data from each car's battery (containing 66 thermal sensors monitoring the pack's nearly 7000 cells) is downloaded, amassed, and analyzed at every service. Tesla's data trove is now so sizable, that sharing insights with its Japanese, Chinese and South Korean cell suppliers is a significant negotiating tool. (By the way, these cells are also now being created specifically for EVs, leaving their laptop origins behind; they're also seeing year-over-year price drops of 6-8 percent). During his presentation later in the day, Kurt Kelty, director of Battery Technology, challenged we journalists to ask-the next time we attend another manufacturer's EV introduction -- exactly what safety precautions they've taken to prevent a runaway thermal event. His expression suggested they don't really have an answer.
This most obvious influence of this safety drumbeat is how the Model S's battery lays like a slab at the bottom of the chassis, benefitting packaging, underbody aerodynamics, and center of gravity issues. Appearing to be about the size of a 4 x 8 sheet of plywood and roughly 4 1/2 inches thick (with the corners scalloped off), the battery's structural encasement, all by itself, offers more torsional rigidity than the Roadster's entire chassis. Internal structures should make it robust enough to satisfy the government's upcoming side pole impact standards, yet it might be removable in about a minute. When asked if this suggests a collaboration with Better Life (proponents of fast-swappable batteries) the answer was no -- but you have to wonder what the purpose of it is, then. The battery enclosure will also be employed as a stiff basis for the Model S's steering rack."
:takeit:
