DE102017200891B4 - Process for producing a pouch cell - Google Patents

Abstract

A method of making a pouch cell comprising:forming an outermost stack including a negative electrode and separators positioned on opposing surfaces of the negative electrode;forming an inner stack including:a positive electrode; andat least one sub-stack having a further negative electrode, a further positive electrode and further separators positioned on opposite surfaces of the further negative electrode;positioning the inner stack on the outermost stack such that i) one end of the inner stack is substantially aligned with one end of the outermost stack, ii) another end of the outermost stack and a portion of the outermost stack remain exposed, and iii) the positive electrode of the inner stack is adjacent to one of the separators of the outermost stack, thereby forming a core stack;the folding the exposed portion of the outermost stack around another end of the inner stack and covering a portion of an outer layer of the inner stack, thereby forming a first overlay; andfolding the core stack by at least a portion of the first overlay after a predetermined number of times.

Description

The present invention relates to a method for producing a pouch cell.

According to the US 2005 / 0 191 545 A1 An electrode assembly is formed by superimposing a film cathode, a film separator and a double-sided film anode to form a stacked structure that is subjected to multiple folds. The initial folding involves folding the cathode in half around the double-sided anode so that the respective upper and lower active anode surfaces are surrounded by it. The multiple folding may comprise one or more successive parallel folds, with the fold line perpendicular to the original length of the stacked structure so that its total length is halved with each fold.

Furthermore, from the publications CN 2 01 084 777 Y and JP S64- 72 460 A Tab attachment methods in which a sandwich structure is formed with a first piece of foil positioned next to an electrode located next to an electrode tab and in which welding the sandwich structure is welded.

INTRODUCTION

Secondary or rechargeable lithium batteries are commonly used in many stationary and portable devices such as: B. encountered in consumer electronics, the automotive and aviation industries. The lithium battery class is becoming increasingly popular for a variety of reasons, including a relatively high energy density, a general lack of any memory effect compared to other rechargeable battery types, a relatively low internal resistance, a low self-discharge rate when not in use, and it can be used in a A variety of shapes (e.g. prismatic) and sizes can be manufactured so that it fits into the designated space in electric vehicles, cell phones and other electronic devices. Additionally, lithium batteries' ability to perform repeated restarts over their remaining lifespan makes them an attractive and reliable source of energy.

SUMMARY

According to the invention, a method for producing a pouch cell is presented. In the process, an outermost stack is formed including a negative electrode and separators positioned on opposing surfaces of the negative electrode. An inner stack is also formed, including a positive electrode and at least one sub-stack having another negative electrode, another positive electrode, and further separators positioned on opposing surfaces of the further negative electrode. The inner stack is positioned on the outermost stack such that i) one end of the inner stack is substantially aligned with one end of the outermost stack, ii) another end of the outermost stack and a portion of the outermost stack remain exposed, and iii) the positive electrode of the inner stack is located next to one of the separators of the outermost stack. This forms a core stack. The exposed portion of the outermost stack is folded around another end of the inner stack and to cover a portion of an outer layer of the inner stack to form a first overlay. The core stack is folded around at least a portion of the first overlay after a predetermined number of times.

A tab fastening method is also described. In the tab attachment method, a sandwich structure is formed with a first piece of foil positioned next to an electrode located next to an electrode tab located next to a second piece of foil. The sandwich structure is welded.

BRIEF DESCRIPTION OF DRAWINGS

• 1A und 1B sind schematische und perspektivische Ansichten eines Beispiels des hierin offenbarten Laschenbefestigungsverfahrens;
• 2A und 2B sind schematische, perspektivische Ansichten eines Teils eines Beispiels des Verfahrens zur Herstellung einer Pouch-Zelle, wodurch eine erste Überlagerung gebildet wird;
• 3 ist eine schematische, perspektivische Ansicht eines inneren Stapels, der an einem äußersten Stapel positioniert ist, wobei ein Ende des inneren Stapels im Wesentlichen mit dem äußersten Stapel ausgerichtet ist;
• 4 veranschaulicht einen weiteren Teil des Beispiels des Verfahrens zur Herstellung der Pouch-Zelle, wobei die erste Überlagerung und Pouch-Zelle dargestellt als schematische Querschnitte dargestellt sind; und
• 5 ist eine schematische und perspektivische Ansicht eines Beispiels einer Pouch-Zelle.

Features of examples of the present invention will become apparent by reference to the following detailed description and drawings, in which like reference numerals correspond to similar, although perhaps not identical, components. For brevity, reference numerals or features having a previously described function may or may not be described in connection with other drawings in which they appear.

• 1A and 1B are schematic and perspective views of an example of the tab attachment method disclosed herein;
• 2A and 2 B are schematic perspective views of a portion of an example of the method of making a pouch cell thereby forming a first overlay;
• 3 is a schematic perspective view of an inner stack positioned at an outermost stack, with one end of the inner stack substantially aligned with the outermost stack;
• 4 illustrates another portion of the example of the method of making the pouch cell, with the first overlay and pouch cell shown as schematic cross-sections; and
• 5 is a schematic and perspective view of an example of a pouch cell.

DETAILED DESCRIPTION

Lithium batteries generally work by reversibly passing lithium ions between a negative electrode (sometimes called an anode) and a positive electrode (sometimes called a cathode). The negative and positive electrodes are arranged on opposite sides of a porous polymer separator that is soaked with an electrolyte solution suitable for conducting the lithium ions. During charging, lithium ions are introduced/inserted into the negative electrode and during discharging, lithium ions are extracted from the negative electrode. Each of the electrodes is also connected to associated current collectors which are connected to an interruptible external circuit through which electrical current can flow between the negative and positive electrodes. Examples of lithium batteries include the lithium-sulfur battery (e.g. a negative electrode with a sulfur-based positive electrode), the silicon-sulfur battery (e.g. a silicon-based negative electrode with a sulfur-based based positive electrode), the lithium-ion battery (e.g. a non-lithium-based negative electrode with a lithium-based positive electrode) and the lithium-lithium battery (lithium-based positive and negative electrodes connected are).

Lithium batteries can have a variety of configurations, including a pouch cell. Some examples of the method disclosed herein form a first overlay and then use a folding or winding process to create a pouch cell. The pouch cell has n-layers of positive and negative electrodes and 2n-layers of separators. This is in contrast to an example of a conventional pouch cell that includes n layers of positive electrodes, n+1 layers of negative electrodes, and 2n+2 layers of separators. This is also in contrast to another example of a conventional pouch cell that includes n layers of positive electrodes, n+1 layers of negative electrodes, and a continuous separator wound between the electrodes, since the continuous separator is often a length longer than 2n+2 layers of the separators. As such, the method(s) disclosed herein utilizes less material, which can increase volumetric energy density.

With certain electrode materials (e.g., lithium negative electrodes, sulfur-based positive electrodes), the electrode in the pouch cell disclosed herein may be formed without a current collector. This can increase the gravimetric and volumetric energy density of the pouch cell. For negative lithium electrodes, this also eliminates the need to cover both sides of the current collector.

The pouch cells also contain tabs that allow the electrodes within the pouch to be addressed. The tab attachment method disclosed herein provides a relatively efficient method of attachment to the individual electrodes. This method eliminates the need for a special die to form a tab attachment location on the electrode. This process can also improve the mechanical properties of the fastener. This method can also increase the contact between the tab and the electrode, for example when compared to contact by a pressing method.

An example of the tab attachment method is in 1A and 1B shown. In 1A a sandwich structure 10 is formed and in 1B the sandwich structure 10 is welded.

The sandwich structure 10 includes a first piece of film 12, an electrode 14, an electrode tab 16 and a second piece of film 18. As shown, the sandwich structure includes a first piece of film 12 positioned adjacent an electrode 14 is located next to an electrode tab 16, which is shown next to a second piece of film 18. In this particular example, the components 12, 14, 16, 18 of the sandwich structure 10 are arranged so that when welded ( 1B) , so that each component 12, 14, 16, 18 contacts the adjacent component (e.g. 12 contacts 14, the contacts 16, the contacts 18) and the electrode 14 and the electrode tab 16 and is between the first and second parts of the Slide 18 is sandwiched.

The first piece of foil 12, the electrode tab 16 and the second piece of foil 18 can be placed anywhere along the length L and the width W (in 1B shown) of the electrode 14 are positioned, it being desirable that the electrode tab 16 is attached to the electrode 14. While 1B As the electrode tab 16 illustrates extending from one side 20B of the electrode 14 after welding, it will be understood that the electrode tab 16 alternatively extends from the other side 20A or from the respective ends 22A, 22B of the electrode 14. Where the electrode tab 16 moves outward from the electrode 14 depends at least in part on the configuration of the last cell.

The electrode 14 may be a negative electrode 14NE or a positive electrode 14 PE. Depending on the material of the electrode 14, the electrode 14 may or may not include a current collector on which the active material (and in some cases binder and conductive filler) is disposed.

Examples of the negative electrode 14NE include lithium metal (e.g., lithium foil) and carbon. The lithium metal and some examples of carbon negative electrodes 14NE are free from the current collector. Other examples of the negative electrode 14NE include graphite, lithium barium titanate, silicon, SiO _x (0<x≤2), silicon alloys (eg, Si-Sn), silicon-carbon composites, tin or tin oxides. These materials are active materials that can be combined with the binder and/or conductive filler and mounted on a nickel or copper current collector to form the negative electrode 14NE. Furthermore, the negative electrode 14 NE is a copper current collector that is charged with lithium.

An example of the positive electrode 14PE includes a sulfur-carbon composite (e.g., the weight ratio of sulfur to carbon is 1:9 to 9:1). The sulfur-carbon composite of the positive electrodes 14PE is free from the current collector. In some cases, the sulfur-carbon composite may be combined with a binder and/or conductive filler to form the positive electrode 14PE. Other examples of the positive electrode active materials 14PE, which may be combined with a binder and/or conductive filler and attached to a current collector to form the positive electrode 14PE. Examples of the positive electrode active material include the spinel lithium manganese oxide (LiMn ₂ O ₄ ), lithium cobalt oxide (LiCoO ₂ ), a manganese nickel oxide spinel [Li(Mn _1.5 Ni _0.5 )O ₂ or a layered nickel manganese cobalt oxide (with a general formula xLi ₂ MnO ₃ ·(1-x)LiMO ₂ , where M is composed in any ratio of Ni, Mn and/or Co. A specific example of the layered nickel manganese cobalt oxide includes (xLi ₂ MnO ₃ ·(1- x)Li(Ni _1/3 Mn _1/3 Co _1/3 )O ₂ ).

Other suitable positive electrode active materials include Li (Ni _1/3 Mn _1/3 Co _1/3 )O ₂ , Li _x+y Mn _2-y O ₄ (LMO, 0 < x < 1 and 0 < y < 0.1 ), a lithium iron polyanionoxide (such as lithium iron phosphate (LiFePO ₄ ) or lithium iron fluorophosphate (Li ₂ FePO ₄ F)), LiNi _1-x Co _1-y M _x+y O ₂ or LiMn _{1 .5-x} Ni _0.5-y M _x+y O ₄ (where M consists of any ratio of Al, Ti, Cr and/or Mg), stabilized lithium manganese oxide spinel (Li _x Mn _2-y M _y O ₄ (where M consists of any ratio of Al, Ti, Cr and/or Mg), lithium nickel cobalt aluminum oxide (e.g. LiNi _0.8 Co _0.15 Al _0.05 O ₂ or NCA), aluminum-stabilized lithium manganese oxide spinel (e.g. Li _x Al _0.05 Mn _0.95 O ₂ ) lithium vanadium oxide (LiV ₂ O ₅ ) Li ₂ MSiO ₄ (where M is from any ratio of Co, Fe and/or Mn) and other high-energy nickel-manganese-cobalt material (HE-NMC, NMC or LiNiMnCoO ₂ ). By “any ratio” it is meant that any element can be present in any amount . So, in some examples, M could be Al, with or without Cr, Ti and/or Mg, or any other combination of the listed elements. In another example, anion substitutions may be made in the lattice of each example of the lithium transition metal based active material to stabilize the crystal structure. For example, any O atom can be substituted by an F atom.

The binder can be used to structurally hold the active material together. Examples of binders include polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), an ethylene propylene diene monomer (EPDM) rubber, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), styrene butadiene rubber carboxymethyl cellulose ( SBR-CMC), polyacrylic acid (PAA), crosslinked polyacrylic acid-polyethyleneimine, polyimide or any other suitable binder material. Other suitable ones Binders include polyvinyl alcohol (PVA), sodium alginate or other water-soluble binders.

The conductive filler may be a conductive carbon material. The conductive carbon material may be a high surface area carbon such as acetylene black (e.g., SUPER P® conductive carbon material from TIMCAL). The conductive filler may be included to ensure electron conduction between the sulfur-based active material and the electrode tab 16.

The first piece of film 12 and the second piece of film 18 can be formed from the same material. For the negative electrode 14NE, the foil pieces 12, 18 can be formed from nickel or copper foil. For the positive electrode 14PE, the foil pieces 12, 18 can consist of aluminum foil. These pieces of film 12, 18 can improve the mechanical properties of the tab fastening.

The material of the electrode tab 16 may also depend on whether the electrode 14 is a positive electrode 14PE or a negative electrode 14NE. An example of a suitable material for the electrode tab 16 of the positive electrode 14PE is aluminum, and examples of suitable materials for the electrode tab 16 of the negative electrode 14NE include copper or nickel.

As mentioned above, once the sandwich structure 10 is formed, the components 12, 14, 16, 18 are welded together. Any suitable welding process can be used, examples of which include ultrasonic welding, spot welding, etc.

The tab attachment method, shown and described in 1A and 1B , can be used to secure the electrode tab 16 to the electrode 14. The electrode 14 can then be used in the example(s) of lithium batteries, including lithium-ion batteries, lithium or silicon-sulfur batteries, lithium-lithium batteries, etc. The type of lithium Battery in which electrode 14 is used depends on the active material in electrode 14.

The electrode 14 can also be used in the example(s) of the method for making a pouch cell. An example of the procedure is in the 2A-2B and 4 shown. 2A and 2 B illustrate the formation of a core stack 24 and the first overlay 26 and 4 illustrates the winding/folding process that results in the formation of the pouch cell 30.

The process for making a pouch cell 30 ( 4 ) involves the formation of an outermost stack 28 and an inner stack 32.

The outermost stack 28 includes a negative electrode 14NE (e.g., the bottom negative electrode 14NE in 2A) and the separators 34 positioned on the opposite surfaces of the negative electrode 14NE.

The inner stack 32 includes a positive electrode 14PE and at least one sub-stack 36. The sub-stack 36 includes another negative electrode 14NE, another positive electrode 14PE, and other separators 34 positioned on opposite surfaces of the other negative electrode 14NE. Although not shown, it is to be understood that the inner stack 32 may include any number of sub-stacks 36 on the positive electrode 14PE.

Each of the separators 34 can z. B. consist of a polyolefin. The polyolefin may be a homopolymer (derived from a single monomer component) or a heteropolymer (derived from more than one monomer component) and may be either linear or branched. When a heteropolymer derived from two monomer components is used, the polyolefin can adopt any copolymer chain arrangement, including those of a block copolymer or a random copolymer. The same applies if the polyolefin is a heteropolymer derived from more than two monomer components. For example, the polyolefin can be polyethylene (PE), polypropylene (PP) or a mixture of PE and PP or a multi-layer structured porous film of PE and/or PP. Commercially available porous separators 34 contain a single layer polypropylene membrane, such as. B. CELGARD 2400 and CELGARD 2500 from Celgard, LLC (Charlotte, NC). It is to be understood that the porous separators 34 may be coated or treated, or uncoated or untreated. The porous separators 34 can, for example, be coated or uncoated or have a surface active treatment.

In other examples, the porous separators 34 may be made of another polymer selected from polyethylene terephthalate (PET), polyvinylidene fluoride (PVdF), polyamides (nylon), polyurethanes, polycarbonates, polyesters, polyetheretherketones (PEEK), polyethersulfones (PES), polyimides (PI), polyamideimides, polyethers, polyoxymethylene (e.g. acetal), polybutylene terephthalate, polyethylene naphthenate, polybutene, polyolefin copolymers, acrylonitrile-butadiene-styrene copolymers (ABS), polystyrene copolymers, polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), Polysiloxane polymers (such as polydimethylsiloxane (PDMS)), polybenzimidazole (PBI), polybenzoxazole (PBO), polyphenylenes (e.g. PARMAX™ (Mississippi Polymer Technologies, Inc., Bay Saint Louis, Mississippi)), polyarylene ether ketones, polyperfluorocyclobutane, polytetrafluoroethylene (PTFE), polyvinylidene fluoride co-polymers and terpolymers, polyvinyl fluoride, liquid crystalline polymers (e.g. VECTRAN™ (Hoechst AG, Germany) and ZENITE® (DuPont, Wilmington, DE)), polyaramides, polyphenylene oxide, and / or combinations of this one. Another example of a liquid crystalline polymer that can be used for the porous separators 34 is believed to be poly(p-hydroxybenzoic acid). In another example, the porous separators 34 may be selected from a combination of polyolefin (such as PE and/or PP) and one or more of the other polymers listed above.

The porous separators 34 may be a single layer or a multilayer laminate (e.g., double layer or triple layer, etc.) from either a dry or wet process.

The porous separators 34 serve as an electrical insulator (preventing a short circuit from occurring), a mechanical support, and a barrier to prevent physical contact between the two electrodes 14NE, 14PE. The porous separators 34 also ensure the passage of lithium ions (labeled Li+) through an electrolyte solution filling its pores.

The method further includes positioning the inner stack 32 on the outermost stack 28 to form the core stack 24, which consists of all components of the inner stack 32 and the outermost stack 28. The positioning of the inner stack 32 on the outermost stack 28 is performed such that i) one end of the inner stack 32 is substantially aligned with one end of the outermost stack 28, ii) another end of the outermost stack 28 and a portion 42 of the outermost Stack 28 remains exposed and iii) the positive electrode 14PE (which is not part of the sub-stack 36) of the inner stack 32 is located next to one of the separators 34 (which are not the outermost separator 34, O) of the outermost stacks 28. Each of these conditions for positioning the inner stack 32 on the outermost stack 28 will be further described.

The inner stack 32 is positioned on the outermost stack 28 so that one end of the inner stack 32 is substantially aligned with one end of the outermost stack 28. By "substantially aligned" is meant that one end 22A or 22B ( 1A and 1B) each electrode 14NE, 14PE and the corresponding one end 38A or 38B of each separator 34 are adjacent to each other or within a suitable distance from the end 22A or 22B or 38A or 38B of the electrode 14NE, 14PE or the separator 34 and the shortest length L of all Components of the core stack 24 have. The ends 22A or 22B and the ends 38A or 38B may be substantially prior to the wrapping/folding process (e.g., as 2A and 3 ) and/or essentially after the winding/folding process (e.g. as in 4 ) be aligned. An example of the substantially juxtaposed ends 22A or 22B and 38A or 38B is shown in FIG 2A shown with all ends 22A and 38A adjacent to one another (e.g., an imaginary vertical plane is formed at ends 22A and 38A). Another example of substantially juxtaposed ends 22A or 22B and 38A or 38B is shown in FIG 3 shown, with all ends 22A and 38A extending a suitable distance from the end 22A of the top electrode 14PE with the shortest length of all components of the core stacks 24. In 3 , the shortest positive electrode 14PE is the top or outermost electrode 14PE in the inner stack 32, and the ends 22A and 38A of each of the electrodes 14NE, 14PE and the other separators 34 extend a suitable distance from the end 22A of the top electrode 14PE. As an example, the appropriate distance for proper alignment may be at least 1 mm. For example, as the core stack 24 moves downward from the top electrode 14PE, the end 38A of each separator 34 and the end 22A of the electrode 14NE, 14PE extends 1 mm longer than the electrode 14NE, 14PE or the separator 34 immediately above it.

With reference to 2A , the inner stack 32 is also positioned at the outermost stack 28 so that another end of the outermost stack 28 remains exposed (ie, not covered by the inner stack 32). It is understood that the other end of the outermost stack 28, shown in 2A , the ends 38B of the two separators 34 in the stack 28 as well as the end 22B of the negative electrode 14NE in the stack 28.

Additionally, as in 2A As shown, the inner stack 32 is also positioned on the outermost stack 28 so that the portion 42 of the outermost stack 28 remains exposed (ie, not covered by the inner stack 32). The exposed section 42 is long enough to be partially folded around another end of the inner stack 32. It is understood that the other ends of the inner stack 32, shown in 2A , which include the ends 38B of the two separators 34 in the stack 32 as well as the ends 22B of the positive electrodes 14PE and the negative electrode 14NE in the stack 32. An example of the partial folding of the exposed portion 42 is shown in 2 B shown. The exposed portion 42 is long enough that when folded, the portion 42 can cover the ends 22B, 38B of the electrodes 14PE, 14NE and the separators 34 of the inner stack 32 and also a portion 44 of the outer layer of the inner stack 32. In the example shown in 2A , the outer layer of the inner stack 32 is the positive electrode 14PE, O.

$$\begin{array}{l}{C}_{Anode}=C_{Fl\ddot{a}chen}\ast Breit{e}_{Anode}\ast Innenl\ddot{a}ng{e}_{Anode}\ast Schichtanzahlen+\\ C_{Fl\ddot{a}chen}\ast Breit{e}_{Anode}\ast dieL\ddot{a}ngedererstenFaltung\ast Au\text{ß}enschichtanzahl\end{array}$$

In order for section 42 to remain exposed after the inner stack is positioned on the outermost stack 28, the negative electrode 14NE and separators 34 of the outermost stack 28 are longer than the negative electrode 14NE, the positive electrode 14PE and other separators 34 of the inner stack 28. In one example, the components of the outermost stack 28 are approximately 4 cm longer than the components of the inner stack 32. The length of the components (and in particular the electrodes 14PE, 14NE) in the respective stacks 28, 32 can be determined at least in part by the charged active material and the desired capacity of the final pouch cell 30 ( 4 ) depend. Examples of equations used to estimate the lengths of the positive electrode 14PE (Equation I) and the negative electrode 14NE (Equation II) include: $$C_{KatHOne}=C_{Fl\ddot{a}cHen}\ast breit{e}_{KatHOne}\ast L\ddot{a}nG{e}_{KatHOne}\ast ScHicHtan\mathrm{e.g}aHlen$$

$$\begin{array}{l}{C}_{AnOde}=C_{Fl\ddot{a}cHen}\ast breit{e}_{AnOde}\ast Innenl\ddot{a}nG{e}_{AnOde}\ast ScHicHtan\mathrm{e.g}aHlen+\\ C_{Fl\ddot{a}cHen}\ast breit{e}_{AnOde}\ast dieL\ddot{a}nGedererstenFaltunG\ast Au\text{ß}enscHicHtan\mathrm{e.g}aHl\end{array}$$

Equation IC _cathode is the capacity of the positive electrode, C _areas is the area capacity and the layer numbers are the total number of layers of the core stack 24. In equation II C _anode is the capacity of the negative electrode, C _areas is the area capacity, inner length _anode is the length of the negative electrode 14NE in the inner stack 32, the layer numbers as the total number of layers of the core stack 24, the length of the first fold equal to the length 42 in 2A and the outer layer number is the total number of layers in the outermost stack 28.

As mentioned above, the inner stack 32 is also positioned on the outermost stack 28 so that the positive electrode 14PE of the inner stack 32 is next to one of the separators 34 of the outermost stack 28. This positive electrode 14PE is the lowest component of the inner stack 32 and is not considered part of the sub-stack 36. This separator 34 is the top component of the outermost stack 28 (e.g. opposite the separator 34, O).

The core stack 24 that is formed includes an n number of positive and negative electrodes 14PE, 14NE and a 2n number of separators 34, with a single separator positioned between the adjacent positive electrodes 14PE and the negative electrodes 14NE.

At 2A the core stack 24 is formed. At 2 B the first overlay 26 is formed. The first overlay is formed by folding the exposed portion 42 around the other end of the inner stack 32 so that it covers the ends 22B, 38B of the electrodes 14PE, 14NE and the separators 34 of the inner stack 32 and also the outer layer portion 44 (e.g B. 14PE, O) of the inner stack 32 cover.

With reference to 4 , the winding/folding process that results in the formation of the pouch cell 30 is shown. On the left side of 4 is a schematic cross section of the core stack 24 and the first overlay 26 2 B shown. On the right side of 4 a schematic cross section of the pouch cell 30 is shown.

To form the pouch cell 30 from the core stack 24 and the first overlay 26, the core stack 24 is folded around at least a portion of the first overlay 26 a predetermined number of times (m). In 4 is the core stack 24 practice the first overlay 26 once (larger due to the left one th, hollow arrow in 4 identified) folded to form the pouch cell 30. Depending on the length of the electrodes 14NE, 14PE and separators 34, the core stack 24 may continue to be folded around the bottom portion of the first overlay 26. The convolution can continue around the first overlay 26 for an m number of times (by the right largest arrow in 4 identified).

Several dimensions of the core stack 24 and the first overlay 26 are in 4 marked. The length L ₀ is the length of the first overlay 26. This length L ₀ can be measured from the end 22B of the electrode 14NE or the end 38B of the separators 34 (overlapping several of the sections 44) to the end 46 of the core stack 24 which is folded exposed section 42 is formed. T ₀ is the total thickness of the core stack 24 and T ' is the thickness of the outermost stack 28.

und die Tiefe D kann nach Gleichung IV bestimmt werden: $$D=\left(m+1\right)\times T_0+T\text{'}$$

At least some of the dimensions of the pouch cell 30 may be determined by the dimensions of the core stack 24 and the first overlay 26. With brief reference to 5 , has a pouch cell 50 configured to the pouch cell 30 shown in 4 , to contain the dimensions of the width W, the depth D and the height H. The width W can be determined according to equation III: $$W=L_0+m\times T_0$$

and the depth D can be determined according to equation IV: $$D=\left(m+1\right)\times T_0+T\text{'}$$

As in 4 As shown, when the winding/folding is completed, the electrode ends 22A and the separator ends 38A at the edge 58 of the wound core stack 24 may be substantially aligned with one another. For example, if the ends 22A, 38A are aligned as shown in 2A shown at the beginning of the procedure, these can essentially be as in 4 be aligned at the conclusion of the procedure. When the ends 22A, 38A are aligned as shown in 4 shown at the completion of the procedure, they may be trimmed to be the same length, as in 2A shown. For another example, if the ends 22A, 38A are aligned as shown in 3 shown at completion of the process, they may be substantially aligned such that ends 22A and 38A are of equal length with one another (e.g., an imaginary vertical plane is formed at ends 22A and 38A) at the end of the process. In this example, the ends 22A, 38A may be pre-cut so that the trimming is not performed at the end of the procedure.

Additionally, at the conclusion of the winding/folding process, each tab attached to the negative electrodes 14NE may be welded together to form a single negative electrode tab 52 ( 5 ) and each tab attached to the positive electrodes 14PE may be welded together to form a single positive electrode tab 54 ( 5 ) to build.

When the pouch cell 30 is completed, it can be sealed in a pouch 56, as shown in 5 shown. An electrolyte may be added to the pouch 56 prior to sealing. The electrolyte used depends at least partially on the electrodes 14NE, 14PE used.

The electrolytes of the lithium-ion battery/pouch cell or the lithium-lithium battery/pouch cell include an organic solvent and a lithium salt which are dissolved in the organic solvent. Examples of the organic solvents include cyclic carbonates (ethylene carbonate (EC), propylene carbonate, butylene carbonate, fluoroethylene carbonate), linear carbonates (dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC)), aliphatic carboxylic acid esters (methyl formate, methyl acetate, methyl propionate), γ -Lactones (γ-butyrolactone, γ-valerolactone), chain structure ethers (1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane), cyclic ethers (tetrahydrofuran, 2-methyltetrahydrofuran) and mixtures thereof. In one example, the electrolyte is a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate. Examples of the lithium salts include LiClO ₄ , LiAlCl ₄ , Lil, LiBr, LiSCN, LiBF ₄ , LiB(C ₆ H ₅ ) ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN(FSO ₂ ) ₂ (LlFSI), LiN(CF ₃ SO ₂ ) ₂ (LITFSI), LiPF ₆ , LiB(C ₂ O ₄ ) ₂ (LiBOB), LiBF ₂ (C ₂ O ₄ ) (LiODFB), LiPF ₃ (C ₂ F ₅ ) ₃ (LiFAP), LiPF ₄ (CF ₃ ) ₂ , LiPF ₄ (C ₂ O ₄ ) (LiFOP), LiNO ₃ , LiPF ₃ (CF ₃ ) ₃ , LiSO ₃ CF ₃ and mixtures thereof. In one example, the concentration of the salt in the electrolyte is approximately 1 mol/L. LiNO ₃ can also be added to the electrolyte as an additive. In these cases the concentration of the lithium salt can be approx. 0.6 mol/L plus the LiNO ₃ additive.

The electrolytes of the lithium or silicon-sulfur battery/pouch cell or the lithium-lithium battery/pouch cell include an ether-based solvent and a lithium salt contained in the ether based solvents can be dissolved. Examples of the ether-based solvent include 1,3-dioxolane (DOL), 1,2-ethylene glycol dimethyl ether (DME) tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,2-diethoxyether, ethoxymethyl ether, tetraethylene glycol dimethyl ether (TEGDME), polyethylene glycol dimethyl ether ( PEGDME) and mixtures thereof. An example of a mixture includes 1,3-dioxolane and 1,2-ethylene glycol dimethyl ether. Any of the previously mentioned salts can be used in this electrolyte. In one example, the concentration of the salt in the electrolyte is approximately 1 mol/l. This electrolyte may also contain another additive, such as LiNO ₃ (along with another lithium salt) and/or a fluorinated ether. When included, the fluorinated ether can be bis(2,2,2-trifluoroethylene) ether (F ₃ C-CH ₂ -O-CH ₂ -CF ₃ ) and/or propylene-1,1,2,2-tetra- Ether (H ₇ C ₃ -O-CF ₂ -CHF ₂ ). The concentration of the fluorinated ether in the electrolyte solution ranges from about 0.1 M to about 1 M.

To further illustrate the present invention, an example is given herein. It is understood that this example is provided for illustrative purposes.

EXAMPLE

A 1 Ah pouch cell was fabricated with a nickel-manganese-cobalt (NMC) positive electrode (on either side of an aluminum current collector) and a current collector-free lithium metal negative electrode. In this way, tabs were attached to each of the electrodes using the method disclosed herein. An aluminum tab was placed next to the positive electrode and both the tab and electrode were sandwiched between two pieces of aluminum foil. The sandwich was ultrasonically welded to secure the aluminum tab to the positive electrode. A nickel tab was placed next to the negative electrode and both the tab and electrode were sandwiched between two pieces of nickel foil. The sandwich was ultrasonically welded to secure the nickel tab to the negative electrode. The two electrodes were stacked with a separator in between. The separator was a polypropylene membrane (CELGARD 2400). In this example, the outermost stack consists of the negative electrode and the separator and the inner stack consists of the positive electrode. This example did not include the additional sub-stacks disclosed herein. A portion of the outermost stack was folded around one end of the positive electrode to form the first overlay and then the core stack (including the negative electrode, the separator and the positive electrode) was folded around the first overlay 9 times to form the pouch -cell to form. Various parameters are shown in the following table. Folding times Total thickness (T ₀ ) (cm) Total width (W) (cm) Li length (cm) Li weight (g) NMC length (cm) NMC weight (g) 9 0.6360 3,225 69.96 2.24 66.18 22.87 Separator weight (g) Tab weight (g) Electrolyte (g) Pouch weight (g) Total weight (g) Energy density (Wh/kg) Capacity (Ah) 1.46 0.2 3.33 2 32.12 346.13 1.11

With a conventional pouch cell design, including Cu foils with tab regions and stacked electrodes and separators, the energy density is approximately 304 Wh/kg. The Cu current collector will be about 4.37 g in the conventional structure.

Elimination of the negative side current collector, using lithium metal as the negative electrode, improves the energy density of the pouch cell disclosed herein.

It is to be understood that the ranges provided herein include the specified range and any value or portion within the specified range. For example, a range from about 0.1 M to about 1 M should be interpreted as including not only the explicitly stated limits of about 0.1 M to about 1 M, but also individual values, such as 0.5 M, 0.75M, etc., and subranges such as from about 0.3M to about 0.9M, etc. Furthermore, when "about" is used to describe a value, it is intended to mean that slight variations of that stated Value is included (up to +/- 10%).

Claims (8)

A method for producing a pouch cell, comprising: forming an outermost stack including a negative electrode and separators positioned on opposing surfaces of the negative electrode; forming an inner stack, including: a positive electrode; and at least one sub-stack having another negative electrode, a further positive electrode and further separators positioned on opposite surfaces of the further negative electrode; positioning the inner stack on the outermost stack so that i) one end of the inner stack is substantially aligned with one end of the outermost stack, ii) another end of the outermost stack and a portion of the outermost stack remain exposed, and iii) themselves the positive electrode of the inner stack is adjacent to one of the separators of the outermost stack, thereby forming a core stack; folding the exposed portion of the outermost stack around another end of the inner stack and covering a portion of an outer layer of the inner stack, thereby forming a first overlay; and folding the core stack by at least a portion of the first overlay after a predetermined number of times. Procedure according to Claim 1 , wherein the inner stack includes a plurality of sub-stacks and wherein the method further includes: trimming an edge of the core stack so that the positive electrodes, the negative electrodes and the separators are substantially aligned with one another at the edge of the core stack. Procedure according to Claim 1 , where the negative electrodes are lithium metals and where the pouch cell excludes a negative side current collector. Procedure according to Claim 1 , wherein the positive electrodes are sulfur-carbon composite electrodes and wherein the pouch cell excludes positive side current collectors. Procedure according to Claim 1 , wherein before forming the outermost and inner stacks, the method further comprises attaching a tab to each of the negative electrodes by: forming a sandwich structure with a first piece of foil, the negative electrode, the tab and a second piece of foil; and welding the sandwich structure. Procedure according to Claim 5 , wherein after folding the core stack, the method further welds the tabs attached to each of the negative electrodes together to form a single negative electrode tab. Procedure according to Claim 1 , wherein before forming the outermost and inner stacks, the method further comprises attaching a tab to each of the positive electrodes by: forming a sandwich structure with a first piece of foil, the positive electrode, the tab and a second piece of foil; and welding the sandwich structure. Procedure according to Claim 7 , wherein after folding the core stack, the method further welds the tabs attached to each of the positive electrodes together to form a single positive electrode tab.

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