In response to my article “Blockchain is not decentralised”, Garycris wrote:

While the developer’s are acting in their own best interest, if you buy into the philosophy of cryptocurrency, then your interests are pretty much aligned with them as well. At the end of the day cryptocurrency will not be successful because it is altruistic, it will be successful because it accepts the reality of human nature, which is that we have unlimited wants and limited resources. This results in greed and lack of trust. Cryptocurrency takes the emotion and judgement out of it.

I’m shocked and terrified by this…

I keep hearing an opinion that “Bitcoin (or any cryptocurrency, or blockchain in general) is decentralised”. It is presented as a “good” property of cryptocurrencies that distinguishes it from older fiat money such as US dollar. Most recently, by Balaji S. Srinivasan:

The people who complain most about filter bubbles are complaining about the plural: there was just one filter bubble they controlled, and now they’re annoyed there’s more than one. The complaint isn’t about filter bubbles, it’s about competing filter bubbles.

The answer isn’t reform, it’s radical decentralization. One component is citizen journalism, where everyone is a journalist, as…

In this post, I want to discuss some of David Deutsch’s positions from “The Beginning of Inifinity”.

“The Beginning of Infinity” is a bold, extremely optimistic hymn to science, and to the growth of human knowledge in general. In fact, one of the key propositions of the book is that the paradigm of seeking good explanations through creativity and criticism (which humanity has used in science since the Enlightenment with astonishing success) applies to art, philosophy, and history as well.

“The Beginning of Infinity” is a rare kind of book which I disagreed a lot with yet wanted to read…

This post is a review of “Analysis of the effect of resistance increase on the capacity fade of lithium ion batteries” by Mandli, Kaushik, Patil, Naha, Hariharan, Kolake, Han, and Choi.

Simple vs. complicated cell models

The authors point out that various research groups suggested many physical cell capacity fade models which sometimes assume very different degradation mechanisms, SEI growth, loss of active material, and Lithium plating:

Ramadass et al [1] have formulated a model attributing the capacity fade to the loss of Lithium inventory on the negative electrode. Safari et al [2] model assumes that the solvent decomposition reaction at the anode leading to…

This is a review of “Investigation of significant capacity recovery effects due to long rest periods during high current cyclic aging tests in automotive lithium ion cells and their influence on lifetime” (2019) by Epding, Rumberg, Jahnke, Stradtmann, and Kwade.

An important but often neglected fact is that privately owned cars spend only a small fraction of their lifetime driving. Long, continuous rest periods of hours (at night, while at work) or even days (over the weekend) are part of most realistic usage scenarios.

I agree. For example, in “Closed-loop optimization of fast-charging protocols for batteries with machine learning”, cells…

This post is a review of “Digital twin for battery systems: Cloud battery management system with online state-of-charge and state-of-health estimation” by Li, Rentemeister, Badeda, Jöst, Schulte, and Sauer.

Can an onboard BMS estimate all cell parameters itself?

With the increase of battery cell number and algorithm complexity, onboard BMS is faced with problems in computation power and data storage for precise estimation and prediction of the battery’s states with model-based algorithms.

I think that sensing is the biggest obstacle to higher-quality monitoring of batteries with many small cylindrical cells: it’s impossible (from cost, power draw, and system engineering points of view) to sense the current and temperature on…

This post is a summary of Hamming’s lectures on simulation (18–20, pp. 128–150). I think this is relevant for this blog because we often need to simulate Li-ion cells and batteries during R&D as well as the real operation.

Hamming’s lectures mostly concern simulations of clear or complicated, but not complex or chaotic systems (in the terms of Cynefin framework). At one place he explicitly says he declined proposals to simulate complex economic and ecological systems. He was prudent: we know the bad reputation of macroeconomic models and simulation.

The good news is that Li-ion cells and battery packs are…

This summary page is largely based on “Li plating as unwanted side reaction in commercial Li-ion cells — A review” (2018) by Waldmann, Hogg, and Wohlfahrt-Mehrens.

Lithium plating is a Cell capacity fade (i. e., a Cell degradation) mechanism. Instead of intercalating into anode, Lithium forms metal compound on the surface of the anode (below the SEI layer on anode).

Lithium plating affects four key characteristics of cells: life-time, low-temperature performance, how fast they can be charged, and the safety.

A physical precondition of Lithium plating is that the standard electrode potential of Lithium intercalating into graphite anode (–2.84) …

The regularisation algorithm described in “Variational Auto-Regularized Alignment for Sim-to-Real Control”:

  1. Simulate inputs
  2. Train VAE’s decoder on the simulated inputs
  3. Train VAE’s encoder with the pre-trained decoder on real inputs
  4. Take the updated simulation parameters from the encoder and repeat from step 1.

This algorithm is analogous to the engineering design process emphasising simplicity:

  1. Collect (or try to predict, i. e. “simulate”) the requirements.
  2. Design the system (or the API) to serve these requirements well, without thinking about the implementation details.
  3. Implement the system and put it into production.
  4. Adjust the requirements based on the feedback and the real usage…

This post is an industrial outlook on the review article “The Application of Data-Driven Methods and Physics-Based Learning for Improving Battery Safety” by Finegan, Zhu, Feng, Keyser, Ulmefors, Li, Bazant, and Cooper (2021).

Li-ion cells are non-linear and non-deterministic systems

The behavior of Li-ion batteries throughout their lifetime is nonlinear, with a plethora of dynamic electrochemical and mechanical phenomena occurring within the cell at any point in time, whether operating or not.

Two cells of identical geometry, chemistry, and history might respond differently when exposed to identical mechanical, thermal, or electrical stimuli.

The authors also state that Li-ion cells are complex systems. I don’t agree with this…

Roman Leventov

Software engineer and designer, author. Working at Northvolt.

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