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Image 1 — The A to Z of Battery Design
Image 2 — The A to Z of Battery Design
Image 3 — The A to Z of Battery Design
▲ 8 r/batterydesign

The A to Z of Battery Design

u/modelmakereditor — 1 day ago
▲ 1 r/EnergyStorage

New Insights into how Cathodes Store Energy

The classical understanding of battery operation relies on a simple ionic model where electrons are exclusively extracted from metal ions (such as nickel or iron) during charging, while oxygen ions act merely as passive bystanders. However, in highly covalent, next-generation materials like nickel-rich and lithium-excess cathodes, this conventional model fails to explain the excess capacity observed, leading to conflicting theories. Most notable is the debate over whether oxygen undergoes dimerisation (forming O₂ bonds) to store charge. This paper seeks to definitively resolve that debate.

Páez Fajardo, G.J., Dogaru, D.E., Banerjee, H. et al. Direct evidence of metal–ligand redox processes in positive electrodes during lithium-based battery operation. Nat. Nanotechnol. (2026).

Overview: https://www.batterydesign.net/new-insights-into-how-cathodes-store-energy/

u/modelmakereditor — 9 days ago
▲ 2 r/batterydesign

Battery Research

We're always interested in seeing the latest battery research, do share papers and patents that you find intriguing or that give you an insight.

reddit.com
u/modelmakereditor — 9 days ago
▲ 3 r/batterydesign

Cell to Pack Design for Renault Megane LFP

2026 Renault Megane E-Tech LFP battery pack with LG Energy Solutions pouch cells and a Cell to Pack design. However, we immediately feel that this isn’t the best battery package when we see Renault’s own description:

>

OK, it's LFP and reduces the cost to Renault by at least 20% https://www.batterydesign.net/2026-renault-megane-e-tech/

However, the layout and frame design looks like something from 10 years ago and definitely not the simplest or lowest cost.

u/modelmakereditor — 13 days ago
▲ 4 r/batterydesign+1 crossposts

Four-Wire (Kelvin) Resistance Measurement

Two-Wire Measurement Fails at Pack-Level Resistance

A two-wire measurement passes current and senses voltage through the same pair of leads, so everything in that loop: lead resistance, probe contact resistance and any spreading resistance at the probe tip adds directly to the reading. A typical 0.5–1m test lead pair, including probe contact resistance, contributes on the order of 50–300 mΩ. Set against typical battery hardware joints of 10µΩ to ~300µΩ and this parasitic resistance can be 100 to 1000 times larger than the value being measured.

Take a laser-welded cylindrical cell tab joint with a true resistance of 80 µΩ. A two-wire measurement with 200 mΩ of combined lead and contact resistance reads roughly 200.08 mΩ, the joint signal is completely buried. The same joint measured four-wire, with current and voltage sensing physically separated, reads the true 80 µΩ regardless of lead length, because the voltmeter’s input impedance is typically in the giga-ohm range: sense-lead current is negligible (picoamps to a few microamps), so the IR drop along the sense leads themselves is negligible.

https://preview.redd.it/wnz2y9b53t8h1.jpg?width=1198&format=pjpg&auto=webp&s=0e26880d3741f7fe9329b41425b671922cb250d9

Recommendations Checklist

  • Use four-wire Kelvin connections for anything below roughly 1 Ω. Essentially every current-carrying joint in a battery pack.
  • Land sense probes directly on the joint or component body, with force probes further out, observing the 1.5×-circumference spacing rule on round conductors.
  • Use current-reversal or OCO compensation where thermal gradients on the bench are likely, and prefer pulsed/short-duration test currents to limit self-heating error.
  • Track contact and joint resistance against a healthy baseline over time rather than relying on a single absolute pass/fail threshold.
  • Specify a true four-terminal Kelvin layout (inner-pad sense routing) for any BMS current-shunt design from the outset. Far cheaper to fix at layout stage than after current-sensing accuracy issues show up in the field.

https://www.batterydesign.net/four-wire-kelvin-resistance-measurement/

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u/modelmakereditor — 16 days ago
▲ 8 r/batterydesign+1 crossposts

How Many Temperature Sensors are Required?

The exact number of temperature sensors you need depends on the size of your battery pack, its physical configuration, rate of charge/discharge (C-rate), and the required level of thermal observability.

In commercial Battery Management Systems (BMS), it is common practice to use one temperature sensor for every 4 to 20 cells, depending on the specific pack design. Installing a physical sensor on every single cell in a high-capacity pack is generally avoided because it introduces excessive manufacturing costs, wiring complexity, and added weight.

Firstly though we should consider this from the thermal viewpoint. The temperature gradient across a cell needs to be <2–3°C as a maximum excursion, and the temperature difference between cells also needs to be <2–3°C [1, 2]. If the temperature gradients and differences are too high, the cells and pack will age very fast, it will be difficult to deliver the energy and power, and maintaining the safety of the pack will require throttling the performance envelope [3, 4]. This means that the electrical and thermal design of the complete battery system needs to be designed around these requirements, and the cell capabilities need to be fully understood.

https://preview.redd.it/ibxo6nc5ee8h1.png?width=1522&format=png&auto=webp&s=9c20f0faa7a9ccc5a606273d196440e76369b7e3

Adding lots of temperature sensors to a poorly designed system will not solve this.

https://www.batterydesign.net/how-many-temperature-sensors-are-required/

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u/modelmakereditor — 18 days ago
▲ 2 r/batterydesign

Electrolyte Motion Induced Salt Inhomogeneity

LiPF6 concentration at the edges of the jelly roll dropped to below one fifth of the value at the center of the cell, built up over repeated fast-charge cycling. Second, teardown photos showed metallic lithium plated on the edges of the negative electrodes after repeated fast charging, while the slow-charged reference cells stayed clean. https://www.batterydesign.net/electrolyte-motion-induced-salt-inhomogeneity/

Read more about:

  • EMSI as a Long-Range Transport Problem
  • Implications for High-energy Li-ion Battery Cell Development & Up-scaling
  • Cell Design Responses and a Reframed Ionic Conductivity Question
u/modelmakereditor — 22 days ago
▲ 2 r/batterydesign

CATL Electrical to Thermal Isolation

Separating the venting and thermal runaway gases from the electrical side will reduce the likelihood of arcing.

CATL engineered the pack by turning the prismatic battery cells upside down. This inverted layout positions all of the electrical terminals, high-voltage busbars, and delicate sensor harnesses safely at the top of the battery pack. Conversely, the explosion-proof pressure relief valves are located at the bottom, pointing downward. More details and links to their patents https://www.batterydesign.net/catl-electrical-to-thermal-isolation/

Venting gases and thermal runaway will significantly reduce the breakdown voltage of the air.

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u/modelmakereditor — 23 days ago
▲ 2 r/batterydesign+1 crossposts

Where do you go if you want battery regulations?

Is this a google search?

How do you find the right definitive list?

How do you find help?

What experience can you tap into?

Asking these questions as I want to find the best way we can help

reddit.com
u/modelmakereditor — 27 days ago
▲ 6 r/batterydesign

CATL and Lithium-Air

Wu Kai identified lithium-air as CATL’s long-term strategic technology direction — the first time the company has publicly named the chemistry as a future product development target. He framed it within a three-horizon roadmap:

  • Near-term: mature lithium-ion technologies (LFP, NMC) to meet current EV and storage market demand.
  • Mid-term: solid-state batteries to deliver the next step in energy density and safety — mass production targeting mid-to-late 2020s.
  • Long-term (post-2030): lithium-air batteries to approach the theoretical limits of electrochemical energy storage.

Wu Kai cited a theoretical energy density of up to 12,000 Wh/kg and referenced current laboratory prototypes exceeding 1,200 Wh/kg. The commercial target he described is EVs with driving ranges exceeding 1,600 km (approximately 1,000 miles) on a single charge.

https://www.batterydesign.net/catl-and-lithium-air/

u/modelmakereditor — 28 days ago
▲ 3 r/batterydesign+1 crossposts

BESS Sizing

A very high level BESS sizing tool https://www.batterydesign.net/bess-sizing/

Battery energy storage systems are specified differently from EV packs. The load profile, cycle regime, and contractual performance requirements all feed into the sizing process — and getting any one of them wrong means either under-delivering on paper or over-spending on hardware. This page walks through the key parameters and the logic that connects them, with a calculator to run the numbers.

https://preview.redd.it/0yx7mtbbgt5h1.png?width=800&format=png&auto=webp&s=8e7a4c9971fe2bed32693269444971be31f65dd3

This is a first-order sizing tool. It does not account for:

  • Availability and redundancy — grid-scale BESS typically carries a system availability guarantee (95–98%); you may need to oversize further or add redundant strings.
  • Temperature derating — capacity and power both derate at low temperatures. Cold-climate installations should add a thermal margin.
  • Project contingency — most procurement engineers add 5–10% on nameplate to cover manufacturing tolerance, cell matching losses, and early-life variance.
  • Chemistry selection — the calculator is chemistry-agnostic. C-rate, cycle life requirements, and operating temperature range all influence whether LFP, NMC, or an alternative makes economic sense for a specific project.
reddit.com
u/modelmakereditor — 1 month ago
▲ 3 r/batterydesign

BatteryDesign.net

We've been chipping away at the pages to improve them, but what do you think: https://www.batterydesign.net/

We have also been improving how it loads, scheduling the order, optimising images, changing plugins etc - all to make it faster and hence a better experience. Is it working?

u/modelmakereditor — 1 month ago