Tesla batteries are composed of thousands of individual lithium-ion cylindrical cells grouped into modules and packs, utilizing either Nickel-Cobalt-Aluminum (NCA), Nickel-Manganese-Cobalt (NMC), or Lithium Iron Phosphate (LFP) cathode chemistries depending on the specific vehicle model and application. What this material choice changes in a real circuit or installation is everything from the pack's nominal voltage curve and thermal runaway threshold to the exact state-of-charge (SoC) limits your Battery Management System (BMS) must enforce to prevent degradation or fire. People most commonly confuse the physical cell format (like the famous 18650 or the newer 4680) with the chemical composition inside the can, assuming a larger cell automatically means a different chemistry, when in fact a 4680 casing can house the exact same NCA or LFP materials as its smaller predecessors.
The Core Chemistries: NCA, NMC, and LFP
To understand what is inside a Tesla pack, you have to look at the cathode. The cathode material dictates the energy density, cycle life, and thermal stability of the cell. Tesla currently relies on three primary lithium-ion chemistries across its vehicle fleet and stationary storage products like the Powerwall. According to the U.S. Department of Energy, the choice of cathode transition metals is the single largest factor in a battery's cost and performance profile.
| Chemistry | Cathode Material | Nominal Voltage | Energy Density (Wh/kg) | Cycle Life (to 80% SoH) | Thermal Runaway Onset | Primary Tesla Application |
|---|---|---|---|---|---|---|
| NCA | Lithium Nickel Cobalt Aluminum Oxide | 3.6V - 3.7V | 260 - 300 | 1,000 - 1,500 | ~150°C (302°F) | Long Range / Performance Vehicles |
| NMC | Lithium Nickel Manganese Cobalt Oxide | 3.6V - 3.7V | 240 - 280 | 1,200 - 2,000 | ~170°C (338°F) | Powerwall / Older Model 3 AWD |
| LFP | Lithium Iron Phosphate | 3.2V | 160 - 190 | 3,000 - 5,000+ | ~270°C (518°F) | Standard Range Vehicles / Megapack |
While the cathode gets the spotlight, the anode is where Tesla has engineered a significant materials advantage. Standard lithium-ion cells use pure graphite anodes. Tesla utilizes a silicon-doped graphite anode. Pure silicon expands by up to 300% during lithiation, which destroys the cell structure. By doping the graphite with roughly 5% to 10% silicon oxide, Tesla increases the cell's energy capacity by allowing more lithium ions to be stored, while the graphite matrix absorbs the physical expansion.
The electrolyte is a liquid solution of lithium salts (typically LiPF6) dissolved in organic solvents, laced with proprietary additives like vinylene carbonate (VC) that form a stable Solid Electrolyte Interphase (SEI) layer on the anode during the first charge cycle. The Argonne National Laboratory notes that SEI stability is critical for preventing electrolyte consumption over thousands of cycles.
Cell Formats vs. Chemical Composition
The most frequent point of confusion for DIYers and tech enthusiasts is conflating the physical dimensions of the cell with its internal chemistry. Tesla uses three main cylindrical formats:
- 18650: 18mm diameter, 65mm height. Used in the original Model S and X. Almost exclusively NCA chemistry supplied by Panasonic.
- 2170: 21mm diameter, 70mm height. Introduced for the Model 3 and Model Y. Houses both NCA (Long Range) and NMC/LFP (Standard Range) depending on the supplier (Panasonic, LG, CATL).
- 4680: 46mm diameter, 80mm height. The current-generation 'tabless' cell used in the Cybertruck and newer Model Y builds. Primarily NCA, but designed with a dry electrode manufacturing process to reduce cost and increase power density.
When sourcing salvaged Tesla cells for a DIY project, you cannot assume the chemistry based on the size. You must read the cell wrapper or test the voltage curve. An 18650 pulled from a salvaged Model S is NCA, but a 2170 pulled from a Standard Range Model 3 is likely LFP. Mixing these up in a DIY build will result in immediate BMS faults or catastrophic overcharging.
Worked Example: Sizing a 14S Solar Pack with 2170 Cells
Let's apply this material knowledge to a real-world installation. Suppose you want to build a 48V nominal (14S) DIY solar storage bank using salvaged Tesla 2170 NCA cells (specifically the Panasonic/Samsung M50 variant, rated at 5.0Ah capacity). Your target is 10 kWh of usable capacity.
Step 1: Calculate Pack Voltage
A 14S configuration using NCA cells (3.6V nominal) yields:
14 cells × 3.6V = 50.4V nominal pack voltage.
Step 2: Calculate Energy per Parallel String
Each parallel string consists of 14 cells in series.
50.4V × 5.0Ah = 252Wh per string.
Step 3: Determine Parallel Strings Needed
10,000Wh target ÷ 252Wh per string = 39.68.
You must round up to 40 parallel strings (40P).
Step 4: Total Cell Count and Physical Mass
14S × 40P = 560 total cells.
At approximately 70 grams per 2170 cell, the raw cell weight is 39.2 kg (86 lbs), excluding nickel strips, busbars, BMS, and enclosure.
Because you are using NCA chemistry, your BMS must be programmed with a strict daily charge limit of 80% to maximize cycle life. For a 14S NCA pack, the absolute maximum charge voltage is 58.8V (4.2V/cell), but your daily absorb voltage should be set to 56.28V (4.02V/cell). If you treat these NCA cells like LFP and charge them to 100% daily, you will halve their cycle life and drastically increase the risk of thermal runaway.
Where You Meet This In Practice: BMS and Thermal Management
Understanding what Tesla batteries are made of directly dictates how you wire, program, and cool them in off-grid or EV conversion projects.
1. BMS Programming and Top Balancing
If you are using LFP cells (from a Standard Range Model 3 or Megapack teardown), the voltage curve is incredibly flat. The cell sits at 3.2V for 90% of its discharge cycle. Your BMS must rely on top balancing (balancing the cells at the very top of the charge curve near 3.65V) because the flat middle curve provides no voltage differential for the BMS to measure state-of-charge accurately. Conversely, NCA and NMC cells have a sloping voltage curve, allowing the BMS to use Coulomb counting and voltage lookup tables for highly accurate SoC estimation without needing to hit 100% charge.
2. Thermal Runaway and Fusing
NCA chemistry has a lower thermal runaway onset temperature (~150°C) compared to LFP (~270°C). In practice, this means a 14S NCA pack pulling high continuous current (like running a 3000W inverter) requires active thermal management or massive copper busbars to prevent resistive heating at the cell tabs. If you are spot-welding 2170 NCA cells, you must use cell-level fusing (thin nickel wire that melts before the cell vents) to prevent a single shorted cell from dumping its entire 5.0Ah capacity into a failed neighbor, triggering a cascading pack fire.
Frequently Asked Questions
Does Tesla still use cobalt in their batteries?
Yes, but the amount is shrinking. NCA and NMC chemistries require cobalt to stabilize the cathode structure. However, Tesla has aggressively shifted its Standard Range fleet to LFP chemistry, which contains zero cobalt, driven by both supply chain ethics and cost reduction. According to the National Renewable Energy Laboratory (NREL), the industry-wide push is to minimize or eliminate cobalt entirely in future iterations.
Can I harvest cells from a Tesla Powerwall for a DIY solar build?
It is highly discouraged. Powerwall cells are heavily potted in structural epoxy and thermal resin to meet strict residential fire codes. Extracting them usually damages the cell wrappers, compromising the insulation and creating a severe short-circuit hazard. Sourcing loose 2170 cells from EV battery teardowns is a much safer and more practical route for DIYers.
