Category Archives: Notebook

Notes on JB Straubel’s Keynote at the 2014 SEEDZ Energy Storage Symposium

I thought I’d share my crude notes on a very interesting talk about energy storage from Tesla CTO JB Straubel. The slides are available as a PDF.

  • JB Straubel Keynote
    • CTO, Tesla
    • Previously CTO & co-founder of Volcom, specializing in high-altitude electric aircraft platforms
    • Board Member, Solar City
  • Why is Tesla Deeply invovled in Energy Storage
    • EV Battery History
      • Status quo was led-acid in 1995
        • Stagnant performance
      • LiIon made possible Tesla and the rebirth of EVs
        • 4x gravimetric energy density
        • 6x volumentric energy density
        • 2x cycle life
      • Tesla was first to do Li-ion R&D for vehicles in 2003
    • Tesla Roadster 2008
      • Sought to challenge internal combustion vehicles on more than just fuel economy
      • ~2,500 sold
      • Largest battery pack in a vehicle
        • 50kWh +
      • Optimism based on progress of LiIon cells
        • ~2x improvement in energy storage capability of batteries in the decade between EV1 era and the Tesla Roadster
          • 300Wh/litr to 600Wh/litre
          • Accompanying weight reduction as well
        • In talking to companies involved in 2005, they saw no reason for progress to plateau
        • Ten years later, they expect progress to continue for the foreseeable future.
        • 40% improvement between introduction of the Roadster and the Model S
          • ~300 miles range
          • 85kWh
          • Smaller pack than the roadster
        • See this trend continuing for the next 10-20 years
        • Only 10-20% away from being able to compete broadly with the internal combustion engine.
    • Long term goal is to sell millions of cars
      • Energy storage is the biggest factor influencing cost, and therefore, volume.
    • Current offerings
      • Roadster
      • Model S
        • Main focus
      • OEM
        • Toyota RAV 4
        • Mercedes-Benz
          • BClass
    • Model S Battery Pack
      • Scale & Scope have enabled a cost point that is competitive in other markets outside cars
      • Utilities
      • Energy density is a key path to lower cost
        • Automobiles
          • Not intuitive
          • Some automobile manufacturers have tried to cut energy to cut costs.
        • 200Wh/Kg
        • Benefits for stationary storage
          • smaller footprint
          • easier retrofit
      • Current costs and projections are on track
      • Manufacturing volume is important too.
        • Goal to build 500,000 Gen3 vehicles/year
          • using capacity in existing Bay Area Plant
        • Energy storage required to meet that goal is another story
        • In 2013 ~34 GWh of lithium ion batteries were manufactured, but from ~21 GWh in 2010.
        • Tesla’s projects to use 3-4GWh in 2014
          • Approximately 10% of WW volume
        • 500,000 Gen3 vehicles/year will require 10x current, or ~35GWh of batteries in 2020.
        • Gigafactory sized to meet that demand
          • Would still only supply 0.5% of WW new car market.
          • Doubling WW capacity
          • Reengineering supply chain with major opportunity for cost cutting
          • 30% cost reduction by 2017 ramp-up
        • Thinks that the market for non-automotive storage will grow even faster than the electric car market.
          • Grid storage is slow to mature, but once you cross certain price thresholds, it becomes a commodity market that sells on cost savings
        • Approach to cost reductions at the gigafactory
          • Looking at everything, including the sourcing of the raw materials.
          • Materials are a meaningful portion of the cost of cells
          • Plan to use their purchasing power to use demand as leverage for sustainable practices throughout the supply chain (labor practices, energy, etc)
        • Gigafactory
          • 35GWh of cells
          • 50GWh of packs
            • 15GWh for stationary packs
              • 10x of the California mandate
  • Tesla and Stationary Storage
    • ~2012 adapted vehicle pack architecture for residential energy storage packs
      • 5kW/10kWh
      • Originally targeted at people with solar and teslas
      • Slow to scale
        • ~1000 systems
      • People who wanted to play with energy in their house
        • Peak demand management
        • “Islanding” to isolate their system from grid and allow operation in the event of a power outage
      • Experiment with aggregation of systems
        • Coordinated across households
        • Business models are a challenge
    • New experiment is a larger-scale system
      • Module
        • Based on model S pack architecture
          • Different arrangement of modules
          •  Same cooling and management
        •  Two hour-rate pack.
          • 200kW / 400 kWh+
        • “Single skid” unit
        • Roughly the size of a shipping pallet
        • 800Kg
      • Pilot deployment
        • SuperCharger location
          • Big enough to be worth the time
          • Very peaky load
            • Up to 250KWh peak demand from cars
            • <100KW peak from meter
      • Thinks that utility side opportunities are significant
        • Backup power
        • Demand management
        • Scale up of renewables
          • This will be the major driver for storage!
        • Major adjustments needed in rate structures/incentives
        • es- I wonder where trends in peak generation costs vs storage costs cross
      • Large Pilot (2013)
        • “One of the bigger installations”
          • Tesla’s Fremont plant
          • 1MW / 5 modules
          • Manages ~10% of peak demand
          • 100 MW substation with 100kV tie.
          • 1-2% of installed grid-attatched storage
          • In the process of doubling capacity
  • Thinks of Tesla is an energy innovation company, more than a car company.
  • Cautionary note about building for economic sustainability, avoiding dependency on incentive programs
  • Innovation needed in storage management technology and relationship to grid and generation
  • “The stone age came to an end not for lack of stones, and the oil age will come to an end not for lack of oil”
  • Thinks the economics of renewables are already compelling and now constrained by storage
  • Q&A
    • Can the world support the scale up from a primary resource point of view
      • Li-ion are primarily graphite/carbon for anode, nickle for the cathode (for their chemistry). Steel for can, polymers for separators, organics for electrolytes
      • Predictions of shortages of lithium aren’t well founded
      • Thinks there is a bubble in lithium prices, but Li-ion costs aren’t the major contributor to lithium cell costs
    • Have you thought about the policy changes needed to drive this change?
      • They have been building relationships with CPUCs and utities and even state and fed regulators, but it isn’t a big focus.
      • Tesla is an innovation company that focuses on creating products that drive the need for regulatory changes.
      • Utilities are conservative. Automotive experience is demonstrating that this technology is ready for utility use.
    • Recyclability of lithium ion batteries
      • Recycling is being built into the Gigafactory. With enough volume there are great opportunities for materials reuse.
      • Challenge now is that growth is so steep that the volume of cells coming back is so much lower than current production
    • What is the commercial lifespan of Lithium Ion batteries?
      • Lithium ion batteries for the next 5-10 years
      • Not waiting for the next big thing…
      • Lithium ion cells make business sense now, which is why they investing.
      • Looking historically, improvements aren’t necessarily revolutionary.
        • Often it is through incremental improvements to components of the system that can leverage a lot of existing infrastructure for building cells and packs
          • Better cathodes
          • Better electrolyte
          • Better separators
        • Thinks we can double energy densities with better anode and cathode materials over the next 10 years.
    • 18650 vs other formats
      • Thinks people are hung up on form-factor for no good reason
      • At the scale they are dealing in what matters is whats inside.
      • What matters
        • Cost of materials
        • Thermal / Safety parameters
      • Their conclusion is that relatively smaller form factor are a reasonable optimization tradeoff between safety, thermal and cost.
        • Slightly larger than an 18650
        • Cylindrical makes sense from a cost perspective
      • Some applications will have different characteristics
      • Large cells just move complexity inside the cell
    • Deployment plan and pricing metrics for fixed storage
      • Depends on market
        • Residential
          • Leased to customer, bundled with larger offering
        • Mid-market commercial customers
          • Many prefer to buy outright
          • Others want Tesla to provide savings, take care of utility interconnect, etc
          • Some people don’t want to arbitrage their energy
            • He did it at his for a while. Got bored with it
          • Thinks at the end of day, Tesla or a 3rd-party financing company will end up owning most of the packs and be responsible for management
        • Utilities are another matter, given the scale and dollars involved.
    • Have you developed a center to deal with dispatch of modules?
      • They are building it.
    • Failure rate and warranty for modules
      • Quite reliable
      • Automotive application is much harsher
      • Maybe over-engineered for fixed application
      • Warranty rates are great
    • Degradation profile
      • Similar to cars
      • Optimized for 10 year life
      • Avoid paying too much for a product that outlasts the product, or the pack.
    • What are your perspectives on the power converter, are you building it yourself?
      • System design and integration are their major focus, just as with automobiles.
      • The power electronics for Tesla Model S is a very capable starting point for these fixed storage modules.
      • Costs for the power electronics are dropping quickly, will see less than $0.10W very quickly.

DIY Programmable Lithium Ion Charger Shield

Update:  According to this comment on Dangerous Prototypes, the charger chip’s support for lithium ion charging is quite primitive, and so this project depends on the Arduino to properly manage the charging. Too bad.

ElectroLabs has published a nicely documented programmable single/multi cell lithium battery charger shield for Arduino. It is based on the LT1510 Constant Current/Constant Voltage Battery charger IC.

Features include:

  • Display for battery/charge status and configuring charging parameters
  • 50mA 10 1.1A charging current.
  • 2-10V charge cut-off voltage

Those voltages don’t make a whole lot of sense for Lithium Ion, but it appears the charger IC they are using also works with other chemistries.

I don’t know the BOM cost, but an assembled version is $75 on Tindie (ouch).

I don’t think I’ll be building one of these, but I am very interested in having examples of using commercial charger ICs outside their default configurations.

[via Hack-a-Day]

Notes from “Why do Li-ion Batteries Die” Lecture

Interesting video of a lecture by Dr. Jeff Dahn, professor of Physics and Chemistry at Dalhousie University in Canada on what causes lithium ion batteries to deteriorate, and how the situation can be improved. Dahn was involved in development of lithium ion battery technology, and maintains an large, active research program devoted to studying materials for batteries and fuel cells.

The video is over an hour long, and the pace is a little slow. I’ll be updating the post with my notes as I go through it.


  • Manufacturer testing and rating of battery lifetime uses a simple cycle test that takes place under a compressed timeframe, with unfortunate results.
    • Charge/discharge cycles are done back-to-back, at charge/discharge rates that might not mirror real-world use.
    • This underrepresent the impact of the parasitic reactions during charge/discharge that lead to cell degradation.
  • During charge and discharge, lithium ions intercalate (intermingle) and de-intercalate with the the electrode material. This causes a modest, “benign” structural change of 3% in the anode and 10% in the cathode.
  • The materials used in lithium cell electrodes are stable in open air, and batteries can be assembled in open air.
    • As cells are charged, the material at both the cathode and anode become highly reactive with the electrolyte solution.
    • Fortunately, the reaction products are solid and form passivating surfaces that protect the electrodes from rapid degradation.
  • For a perfect Li-ion battery, the coulombic efficiency, the number of electrode in during charging vs the electrons out during discharge, should be exactly 1.
  • The difference between theoretical and actual coulombic efficiency, outside of the measurement area, is attributable to  undesirable parasitic reactions that lead to cell degradation.
  • With sufficient measurement precision, it is possible to predict lithium cell lifetime without intensive testing.
    • Requires at least 4 digits of precision and accuracy
  • Battery Electrolyte
    • Cyclic and linear organic carbonates
      • Ethylene Carbonate
      • Propylene Carbonate
      • Dimethyl Carbonate
      • Ethylmethyl Carbonate
    • Lithium Phosphorous Hexafluoride solute
    • Solvents are typically mixed
      • Some have low boiling points
      • Others form excellent passivating layers
  • Approximate 3-billion 18650 cells made a year
  • Parasitic reactions between electrodes and electrolytes reduce the capacity of the cell as lithium ions are consumed/trapped
    • Capacity change after first charge/discharge cycle is relatively large.
    • Loss in subsequent cycles is lower, because the reaction products form a passivating layer that protects the electrodes.
  • Extent of parasitic reactions can be quatified with a precise measure of coulombic efficiency.
    • A good cell is close to 100%.
    • 10,000 cycle life would require a cell with 99.99% efficiency
    • Need 4th digit in accuracy and precision.
  • Precision charging device
    • Developed by
      • Aaron Smith, PhD, graduated in 2012, now at Tesla in charge of Tesla’s Battery Lifetime Group
      • Chris Burns, PhD Student
    • Specs
      • 60 channels, each with precision current supplies with 5 digit precision
      • Cells under test are in temperature controlled boxes ( 0.05C)
      • Current is fed through precision resistors to measure current.
  • Longer charge cycles have higher coulombic inefficiency, and therefore more destructive parasitic reactions.
  • Coulombic Ineficiencies of common chemistries
    • Test conditions
      • Commercial 18650 cells, two per test condition
      • Charge / Discharge rates: C/24, C/50, C100
      • 30C, 40C, 50C, 60C
    • High-level
      • Coulombic inefficiency has linear relationship to charge time.
      • Strongly suggests that time under charge is the major factor in determining coulombic inefficiency for a given chemistry, at a given temperature.
    • Lithium Cobalt Oxide (LiC02)
      • Lowest parasitic reactions at 30°C
      • Moderate at 60°C, but still lower than Lithium Manganese Oxide at 30°C
      • Tesla has used chemistries with similar characteristics
    • Lithium Cobalt Manganese Oxide (Li[NiMnCo]02)
      • Moderate at 30°C
      • ~50% of Nissan Leaf and Chevy Volt packs
    • Lithium Iron Phosphate (LiFePO4)
      • Moderate parasitic reactions at 30°C, high at 60°C
      • Used by Fiskar
    • Lithium Manganese Oxide (LiMn02)
      • Highest parasitic reactions of all examples at 30°C and even worse at 60°C
      • ~50% Part of the Nissan Leaf and Chevy Volt battery pack
      • Ill-suited to use in battery packs without thermal management, like the Nissan Leaf.
  • Electrolyte additives
    • Vinylene Carbonate: reduces electrolyte oxidation on positive electrode. 2% by weight makes a huge difference
    • Trimethoxyboroxine, 1-3 propane sultone: impedence reducers.
    • Triethylphosphate and others: wetting agents to aid speed in manufacutre
    • Others for lifetime, low or high temp performance, and safety
    • Typical Li-ion cell will have 5 additives
  • Precision coulombic efficiency measurements allow impacts on cell lifetime to be assessed relatively quickly, traditional testing of discharge capacity vs cycle number requires testing to end-of-life.
    • Short term test results correlate with long term test results
  • Predicting catastrophic failures
    • Hypothesis
      • Reaction byproducts from cathode are migrating to anode, where they are reduced and gradually foul the material until the pores in the anode material are clogged. Once the pores are clogged, lithium starts plating out, and cell capacity plummets.
    • Predictions
      • The more compacted the anode material, the sooner the cells will fail.
        • This predicted behavior has been observed, and exploited to make cells that are designed to fail early in order to test other variables.
      • Coulombic Inefficiency * Cycles = A Constant
        • Coulombic Inefficiency = amount of byproducts
        • Constant is the amount of material required to clog the pores
        • A strong correlation has been observed for many additives
    • Exceptions
      • Some unknown additives from battery manufacturers have been tested and shown that make huge (20x) contributions to cycle life while falling outside the predictive model
      • Model assumes a solid reaction byproduct on negative
      • Additives may produce a reaction byproduct with different characteristics (ie liquid, gas)
    • Other observations
      • Coulombic efficiency and cycle life tend to increase with the number of additives
        • And yet most academic research on electrolyte additives only looks at one at a time.
  • New grant to put a 100 channel system on line with the capability of testing automotive scale cells
    • 10 ppm CE accuracy
  • Research Directions
    • Tests require highly uniform cells. Lab made cells can be rather inconsistent
    • Have established relationships with Chinese manufacturers of pouch cells
      • Get machine-made pouch cells without electrolyte in lots of 2,000
      • Mix and add electrolyte themselves.
      • Seal cells in vacuum sealer
    • Microcalorimeter
      • Measure the heat from parasitic reactions
      • TA Instruments TAM III
        • 12 separate calorimeters
        • 10nW sensitivity
        • Baseline stability of 500nW/month
        • Isothermal, all experiments at 40C
        • Holds AA and 200mAh cells.
      • Three sources of heat during charging (~1Wh cell capacity)
        • Entropy changes from electrodes
        • Internal resistance/polarization
        • Parasitic reactions
          • 100 uW would consume all the electrolyte in a year BAD
  • Questions from audience
    • Audience asked about the unknown additive outliers that didn’t conform to the simple model of reaction products clogging the pores on the anode.
      • Dahn replied that if those additives formed a liquid or gas reaction product, then one would expect the impedance to be lower. He then showed data showing that, indeed, the cells with outlier additives did have lower impedence.
    • Asked about using these techniques with silicon electrodes.
      • Silicon electrode cells at this point are so poor, that you can see the parasitic inefficiency with an ordinary charger.
      • Silicon electrodes need a lot of development before they need this precision.
      • Lithium Titanate
        • Incredibly durable already.
    • How can these metrics be applied to drive cycles?
      • GM wants to relate this to drive cycles.
        • Dahn’s initial approach is:
          • How does existing technology work for driving?
          • How does it look with precision charging?
          • What are the new technologies?
          • How do they perform under precision charging?
          • Based on result, he can say if the new stuff should be better or worse.
    • How do real-world discharge profiles relate to constant discharge rates seen in lab tests?
      • The biggest factor is time spent at highest voltage.
        • Longer is worse
        • Most of the parasitic reactions happen above 4v.
    • Lithium Ion Cell Overhang
      • Negative Electrode is slightly wider than the Positive
      • Prevents lithium ions from the positive electrode from plating out the edge of the negative and forming lithium metal dendrites
      • There is an overhang of graphite
      • At the beginning of charging there is some odd behavior as the ions equilibrate with the overhang
    • To extent the life of your phone or laptop battery
      • Keep it as cold as possible 🙂
      • Put it in the fridge.

Dell and Thinkpad Lithium Ion Pack Irritation

I got a bunch of Thinkpad Lithium Ion battery packs yesterday and dumped pack data out of all of them. The new packs had the same issue I saw with a pack for a different module, they don’t report individual cell voltages in response to commands that work with many other packs.

I did some research and found that the linux tm-smapi module provides access to individual cell voltages but from a little reading, it looks like this information may come by way of an embedded system controller. I figured there was still a good chance that this information was originally gathered from the battery via SMBus, so I wrote a simple arduino sketch to scan through a wide range of SMBus commands and look at the data returned. Unfortunately, I don’t see any values that look like cell voltages.

With any luck, the data is still there, and just packed in a way that isn’t obvious. I think I’m going to need to collect data from multiple packs to see which values differ, particularly if I charge or discharge the packs. The worst possible option is that reading the data requires putting the pack in an undocumented mode and using undocumented commands.

The Dell packs I have don’t yield individual cell voltages either, so while I was at it, I also looked to see if any of the Dell packs might report the data in response to non-standard commands. Again, nothing obvious. I couldn’t find any confimation on line that Dell makes this info available via any utilities, so I may be chasing something that isn’t there.

Inside look at HP’s approach to laptop batteries (circa 2012)

While trying to find details of what’s inside HPs extended runtime batteries, I came across video shot by Tom’s hardware of a press junket / meet-and-greet with Dr. John Wozniak from HP talking about what goes into designing and HP’s battery packs.

It’s from spring of 2012, which makes it a bit dated in some regards, but I still found it informative, particularly since most of the battery packs I’m getting are of a similar vintage.

Some things I found interesting:

  • Relative to 18650 cells, prismatic LiIon are ~1.4x more expensive, and pouch packs are 2x more expensive for the same capacity.
  • At the time, 18650 cells were clearly HPs focus for price/capacity. They were, however, using prismatic cells and pouch-packs for thinner form factors.
  • Pouch cells are relatively easy to get 1000 charge cycles from because they can expand and contract as needed when being charged and discharged, reducing the pressure that degrades the electrodes. The downside is that cells can also expand due to gas generation, which can damage the pack and/or other components.
  • At least for the products being discussed, HP seemed to be transitioning from prismatics to pouch packs.
  • Safety regulations limit companies from stuffing more than 100Wh into a single battery pack. This, combined with improved capacities, have lead to the demise of 12-cell extended runtime packs.
  • At the time, HP was using LG 3000 mAh cells for their high-capacity 18650 packs.
  • Apple shouldered the growing-pains of getting pouch-cell pack design and manufacturing right.
  • Because the cells are a commodity, HP tries to distinguish its packs on quality, reliability and manufacturability. This has led them to use conformal coatings on circuit boards to protect against shorts and corrosion. They’ve also switched from wires to flex circuits within the packs for improved reliability and their pouch-cell packs have moved to welding the cell contacts directly to a PCB.
  • Their primary suppliers are Panasonic, LG, Samsung.
  • Among Chinese cell manufacturers, they’ve tried to work with a few, but the economics haven’t worked out. B&K is a qualified supplier for some of their packs, but HP doesn’t ship many of their cells.

HP TD06 (Series HSTNN-UB85) 11.1V 62Wh battery pack teardown

I picked this HP TD06 (Series HSTNN-UB85) 11.1V 62Wh battery pack up at RePC for $1 at the same time I got the ASUS AL32-1005 pack I posted about earlier. Based on the nameplate pack voltage, it was one of only a handful that used newer 3.7v lithium ion cells out of the hundred or more packs they had.


It was also the only of TD06 pack using newer cells; there were 3-4 labeled with a 10.8v voltage.

Peeling the label back gave a tiny peak at the cells. I was able to separate the two halves of the pack case with a thin bade, pliers and a bit of elbow grease.


The lavender-wrapped cells are clearly made by Samsung (not a big surprised, given that the pack label indicated that the cells were made in Korea. The remaining marking is ICR18650-28A. These cells are rated for 2800 mAh of charge capacity, which isn’t a surprise given the 62Wh claim. Unfortunately, they must be charged to 4.3V to achieve that capacity. When charged to the more common 4.2V, they have about 7.5% less capacity.

The battery management seems to be divided between two chips with a lot of pins.  One is labeled M37512, FC024, J2C5D. The other is 20020 ??05. The first chip appears to be an 8-bit M37512-FC MCU from Renesas intended for…battery pack applications. I’m not sure what the second chip appears to be a RS20020. This is a companion chip for battery pack applications. I can’t find information on what it does, exactly, but it seems to have connections to each cell, and to the MOSFETs that can switch the flow of current to or from the pack on and off.

ASUS AL32-1005 11.25V 5600mAh 63Wh battery pack teardown

I picked this ASUS AL32-1005 11.25V 5600mAh 63Wh up at RePC for $1. Based on the nameplate pack voltage, it was one of only a handful that used newer 3.7v lithium ion cells out of the hundred or more packs they had.



Labels for the positive and negative contacts were, helpfully, molded into the plastic.


Removing the plastic sticker exposed part of the cells, but to get them out, I had to rip the plastic case apart, with some pliers and elbow grease. Pack voltage is reasonable, so its unlikely that any of the cells are completely shot, but at the point, I don’t know how much use they’ve suffered. I’m leaving the circuit intact for now so I can try and read out the smart battery information so I can see if there is any correlation between that and the results of testing the individual cells.

The cells themselves look like they are made by LG. They are all labelled LGDC118650. All the onces I can see also have I1245xxxxxx, MED45DxC1, where the ‘x’ represents a position with a number or letter that varies from cell to cell.

From what I can tell, the manufacturer is LG, and they are 3.7V, 2,800mAh cells, which is pretty much what I expected based on the specs printed on the outside. One of the only english-language pages I found mentioning these cells suggested they had a charge termination voltage of 4.35v, but I’ve found nothing else to corroborate that.

The battery management chip is labeled bq 20Z45, 95K, CP7L, which looks like the TI bq20z45, an all-in-one battery management chip.



Notes: Smart Battery Hacking 2014-08-27

I’m trying to read out information from three different laptop batteries by taking advantage of the smart battery system interface.

The batteries are:

So far, I haven’t had any success in reading out data from any of the batteries, but I have figured out the pinout of the connectors:

MacBook Pro Battery ConnectorIMG_6028

From left to right, inside the wide guide slots on either side:

  • P-
  • Temperature
  • Data (SMBus)
  • Clock (SMBus)
  • Unused
  • P+

 Acer Battery Connector


From left to right, inside the wide guide slots on either side:

  • P-
  • P-
  • Data (SMBus)
  • Clock (SMBus)
  • Temperature
  • Battery Activate / Enable
  • P+
  • P+

The MacBook Pro battery packs make power available all the time, while the acer batteries require a short or low resistance connection between the P- (system ground) and the Battery Activate pin in order to “wake” the battery so it will present voltage, or receive charging current. Furthermore, the Acer packs only wake up briefly if the overall pack voltage is below ~9v or so.

I’m currently using an arduino and using this post as a starting point on how to (try) to talk to a smart battery.