Battery pack - Revision history

SpookySimon: /* Cans vs pouches */ plurality agreement

2024-04-05T14:09:53Z

Cans vs pouches: plurality agreement

SpookySimon: /* Cans vs pouches */ reference

2024-04-05T14:08:36Z

Cans vs pouches: reference

SpookySimon: /* LFP */ reference

2024-04-05T14:07:10Z

LFP: reference

SpookySimon: /* Cell selection */ reference

2024-04-05T14:02:17Z

Cell selection: reference

SpookySimon: /* Chemistry */ intro to lfp.. this will probably need a lot of work

2024-04-05T13:48:24Z

Chemistry: intro to lfp.. this will probably need a lot of work

SpookySimon: /* Chemistry */ chemistry intro

2024-04-05T13:45:59Z

Chemistry: chemistry intro

SpookySimon: Adding references section

2024-03-19T17:46:43Z

Adding references section

SpookySimon: adding sections for chemistry discussion

2024-03-19T17:44:23Z

adding sections for chemistry discussion

SpookySimon: /* How to properly use a battery pack */

2024-03-19T17:38:51Z

How to properly use a battery pack

SpookySimon: /* Thermal loads */ more on thermal loads

2024-03-19T17:37:14Z

Thermal loads: more on thermal loads

@@ Line 25: / Line 25: @@
 ===Cans vs pouches===
-The most common  form factors for lithium cells are the can (i.e. 18650) or in soft metal-plastic pouches <ref>https://www.rosebatteries.com/blog/most-popular-lithium-ion-cells-for-custom-battery-packs</ref>. It is easier to design a safe battery pack with cylindrical cells as each cells are protected in a hard shell that protects them from accidental perforation. Cylindrical cells tend to offer higher energy density, while pouches tend to offer higher power density. Cylindrical cells can be spot welded together with fairly inexpensive equipment, while pouches can be connected together by ultrasonic welding, laser welding, or mechanical assembly (rivets, nuts & bolts, ...). While cylindrical cells are typically found in small capacities ( < 4 Ah ), pouches can be found in high capacities ( > 10 Ah), greatly reducing the complexity of assembly of a battery pack, since fewer cells are required to meet the battery pack energy requirement.
+The most common  form factors for lithium cells are the can (i.e. 18650) or in soft metal-plastic pouches <ref>https://www.rosebatteries.com/blog/most-popular-lithium-ion-cells-for-custom-battery-packs</ref>. It is easier to design a safe battery pack with cylindrical cells as each cell is protected in a hard shell that protects them from accidental perforation. Cylindrical cells tend to offer higher energy density, while pouches tend to offer higher power density. Cylindrical cells can be spot welded together with fairly inexpensive equipment, while pouches can be connected together by ultrasonic welding, laser welding, or mechanical assembly (rivets, nuts & bolts, ...). While cylindrical cells are typically found in small capacities ( < 4 Ah ), pouches can be found in high capacities ( > 10 Ah), greatly reducing the complexity of assembly of a battery pack, since fewer cells are required to meet the battery pack energy requirement.
 ====Pouches====
 Pouches offer better heat dissipation than other type of cells, but their flexible and thin envelope make them prone to perforation or crushing. Some pouches have tabs on the same edge, some, on opposite edges. Opposite edge tabs allow better heat dissipation, but make packaging more complex. They stack easily, using most of the available space. The cells edges are fragile: treat them with care. It is preferable to ask the cell manufacturer to have the edges taped. Most pouches will ignite in case of a nail penetration. One way to reduce the risk it would ignite is to improve the cooling of the cell. As an example, using sheets of metal between cells would spread the heat (and evacuate it out of the cell).

@@ Line 25: / Line 25: @@
 ===Cans vs pouches===
-The most common  form factors for lithium cells are the can (i.e. 18650) or in soft metal-plastic pouches. It is easier to design a safe battery pack with cylindrical cells as each cells are protected in a hard shell that protects them from accidental perforation. Cylindrical cells tend to offer higher energy density, while pouches tend to offer higher power density. Cylindrical cells can be spot welded together with fairly inexpensive equipment, while pouches can be connected together by ultrasonic welding, laser welding, or mechanical assembly (rivets, nuts & bolts, ...). While cylindrical cells are typically found in small capacities ( < 4 Ah ), pouches can be found in high capacities ( > 10 Ah), greatly reducing the complexity of assembly of a battery pack, since fewer cells are required to meet the battery pack energy requirement.
+The most common  form factors for lithium cells are the can (i.e. 18650) or in soft metal-plastic pouches <ref>https://www.rosebatteries.com/blog/most-popular-lithium-ion-cells-for-custom-battery-packs</ref>. It is easier to design a safe battery pack with cylindrical cells as each cells are protected in a hard shell that protects them from accidental perforation. Cylindrical cells tend to offer higher energy density, while pouches tend to offer higher power density. Cylindrical cells can be spot welded together with fairly inexpensive equipment, while pouches can be connected together by ultrasonic welding, laser welding, or mechanical assembly (rivets, nuts & bolts, ...). While cylindrical cells are typically found in small capacities ( < 4 Ah ), pouches can be found in high capacities ( > 10 Ah), greatly reducing the complexity of assembly of a battery pack, since fewer cells are required to meet the battery pack energy requirement.
 ====Pouches====
 Pouches offer better heat dissipation than other type of cells, but their flexible and thin envelope make them prone to perforation or crushing. Some pouches have tabs on the same edge, some, on opposite edges. Opposite edge tabs allow better heat dissipation, but make packaging more complex. They stack easily, using most of the available space. The cells edges are fragile: treat them with care. It is preferable to ask the cell manufacturer to have the edges taped. Most pouches will ignite in case of a nail penetration. One way to reduce the risk it would ignite is to improve the cooling of the cell. As an example, using sheets of metal between cells would spread the heat (and evacuate it out of the cell).

@@ Line 20: / Line 20: @@
 ====NMC====
 ====LFP====
-LFP batteries have become highly utilized in EVs due to their high performance and thermal durability.
+LFP batteries have become highly utilized in EVs due to their high performance and thermal durability. <ref>Ferreira, Summer. <em>Thermal stability study of commercial
 ===Cans vs pouches===

@@ Line 15: / Line 15: @@
 The pack may be required to meet other goals such as packaging requirements, mass, cost, material specification, etc. These can preclude meeting design goals, particularly capacity. Correctly prioritizing team and system goals will be critical in making these compromises.
 ==Cell selection==
-The selection process of a lithium-ion/lithium-polymer cell is highly dependent on the application. Before even starting battery pack design, it is crucial to understand the operating conditions. A light-weight car with 2WD requires less power than a heavy 4WD car with a full aero package. Because there is a trade-off between cell energy density (Wh/kg) and cell power density (W/kg), it is then possible to compare the performance of cell chemistries using lap simulation: there are cases where a higher specific energy cell is optimal, and others where high specific power is.<!-- I think it would be advantageous to explain what these cases are -->
+The selection process of a lithium-ion/lithium-polymer cell is highly dependent on the application. Before even starting battery pack design, it is crucial to understand the operating conditions. A light-weight car with 2WD requires less power than a heavy 4WD car with a full aero package. Because there is a trade-off between cell energy density (Wh/kg) and cell power density (W/kg)<ref>https://commons.wikimedia.org/wiki/File:Lithium_Ion_Capacitor_Chart.png</ref>, it is then possible to compare the performance of cell chemistries using lap simulation: there are cases where a higher specific energy cell is optimal, and others where high specific power is.<!-- I think it would be advantageous to explain what these cases are -->
 ===Chemistry===
 Most batteries used in EVs will have a lithium based chemistry. The two main lithium chemistries are nickel manganese cobalt oxides (NMC) or lithium iron phosphate (LFP). NMC batteries are an older technology, and are more common and cheaper in most configurations. While cobalt is not legally defined as a "conflict mineral", the extraction is closely tied to human suffering<ref>Dasilva, Jeremy. <em>Conflict Implications of Rising Cobalt Demand and the Effects of Classifying Cobalt as a Conflict Mineral on the DRC</em>. 2022. Johns Hopkins, Masters Thesis. <em>JScholarship Library</em> https://jscholarship.library.jhu.edu/server/api/core/bitstreams/b2780da6-5830-4b07-8a23-a5d09051b9f5/content</ref>. This alongside the relative rarity of the element has lead to a push for non-cobalt battery chemistries<ref>https://www.mitsubishicritical.com/resources/blog/the-runaway-review/lithium-nickel-manganese-cobalt/</ref>.
@@ Line 33: / Line 33: @@
 ===Cells capacity vs safety===
 At the cell level, a smaller capacity cell is safer than a higher capacity cell: a small capacity cell may not store enough energy to generate a thermal runaway. However, it is false to assume that a huge capacity pouch is more dangerous than a couple of low capacity cells put in parallel. High capacity cells are made under extremely high quality control, while low capacity 18650s are not: it's more cash efficient to discard under performing these cells. Discarding a 240 Ah cell would be extremely costly for a manufacturer. Also, high capacity cells include various safety techniques (including internal self fusing) which intent is to prevent a problematic layer of the cell to make the cell enter a thermal runway.
 ==Arrangement of cells==
 Cells can either be connected in series (positive to negative) or parallel (positive to positive, negative to negative). Connecting cells in series raises the pack voltage, and connecting them in parallel increases the energy capacity. So if you have two 3.6V 3Ah cells, connecting them in series gets you a 7.2V 3Ah battery pack. Connecting them in parallel gets you a 3.6V 6Ah battery pack.

@@ Line 20: / Line 20: @@
 ====NMC====
 ====LFP====
 ===Cans vs pouches===

← Older revision		Revision as of 17:46, 19 March 2024
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	* In a stable position.		* In a stable position.
	* In a well ventilated area.		* In a well ventilated area.
		+	=References=
		+	<references />

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 The proper usage of the battery shall be limited by the battery management system (BMS). Here's a list of advice:
 * As per the rules, avoid exceeding 60 Celsius degree.
-* Do not overcharge (generally over 4.2V), nor over discharge (generally under 2.7V).
+* Do not overcharge the cells (generally over 4.2V each), nor over discharge the cells(generally under 2.7V each).
 * As per the rules, ensure that the battery pack design does not allow the drop of tools to create a short circuit.
 * Ensure that all conductive materials in the battery pack is grounded.

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 The battery pack must resists to impacts and vibration. Bolts need to have positive locking mechanism. The battery pack should be built strong enough in a way that cells are not crushed in case of a drop on one of its corners.
 ===Thermal loads===
-Lithium-ion cells don't like heat. As per the rules, cells exterior casing shouldn't reach 60 Celsius. Although it's easy to circumvent the rules here, no one should do it.
+Lithium-ion cells don't like heat. As per the rules, cells exterior casing shouldn't reach 60 Celsius. Although it's easy to circumvent the rules here, no one should do it. The heat sources may be external such as the motors, inverters, solar load, etc. or internal from heat generated by the module's internal resistance.
 ===Safety===
 Sharp edges inside the battery pack should be avoided. Appropriate clearance between wires should be maintained. Ensure that large voltage differences are far from each other. Positive locking mechanisms should ensure that screws don't loosen. It should be impossible to create a short circuit in case of the drop of tools. Think what could go wrong in case of an accident, and try to prevent it.