EA039132B1 - Lithium ion battery and method of manufacturing same - Google Patents

Abstract

A method for producing a lithium ion battery is disclosed. The method comprises the following steps: assembling a cell including an interior volume comprising an anode, a cathode, and a separator; filling the interior volume of the cell with an electrolyte; connecting the anode and the cathode to a charging device; charging the cell at a rate less than or equal to C/6 until the cell reaches a voltage capacity; and charging the cell at a voltage for greater than 6 h. The invention further encompasses such a method wherein the voltage capacity is greater than or equal to 3.4 V. The invention further encompasses such a method wherein the voltage is greater than 3.4 V. The resultant batteries may comprise an efficient and properly formed solid electrolyte interface layer.

Description

Technical field

The present invention relates to a method for manufacturing a lithium ion battery comprising an insulating (non-conductive) microporous polymer battery separator composed of a single layer of intertwined microfibers and nanofibers. The general fabrication method is highly efficient and provides a complete solid electrolyte interfacial layer (SEI layer) on the anode of the battery. A method for manufacturing such a separator, a method for using such a separator inside a battery, and a method for manufacturing a solid electrolyte interfacial layer are included within the protection scope of the present invention.

State of the art

For many years, batteries have been used for electrical energy storage in remote locations and for portable applications. As a result of the controlled movement of ions between the electrodes (anode and cathode), a power supply circuit is formed, thus providing a source of electricity that can be used until the excess ions on one electrode are exhausted, after which further generation of electricity stops. Recently, rechargeable batteries have been developed to provide extended lifetimes for such remote power sources, even with the need to connect such batteries to other sources of electricity for a certain period of time. However, in general, the reusability of such a battery has opened up great prospects for use, in particular in a cell phone and laptop, and, moreover, the possibility of creating cars that run solely on electricity.

Such batteries typically contain at least five different components. The case (or container) houses the rest of the components in a safe and secure manner to prevent leakage to the outside, as well as contact between the outside and the inside. The housing contains the anode and cathode, reliably separated by a separator, as well as an electrolyte solution (low-viscosity liquid), which transports ions through the separator between the anode and cathode. Rechargeable batteries are currently and are expected to be used in the future in a variety of portable devices that are fairly small, but have a large potential for generating electricity, allowing them to remain efficient for long periods between charges, up to very large batteries, such as those found in cars. , which contain large electrodes (at least in terms of surface area) that must not come into contact with each other, and a large number of ions that must sequentially and constantly pass through the membrane to form the electrical circuit necessary to generate electricity sufficient to run the engine car. Also, the functionality and versatility of battery separators in the future must meet certain requirements that are not yet developed in today's industry.

In general terms, battery separators have been used since the advent of sealed cell batteries to provide the necessary protection against unwanted contact between electrodes, as well as to ensure efficient transport of ions within the power generating cells. Typically, such materials have a film structure that is thin enough to reduce the weight and volume of the battery device while imparting the desired properties indicated above. Such separators must have other characteristics, as well as ensure proper operation of the battery. These characteristics include chemical resistance, suitable porosity of ionic forms, effective pore size for electrolyte transfer, proper permeability, effective mechanical strength, and the ability to maintain dimensional and functional stability when exposed to high temperatures (as well as the ability to shut down if the temperature rises to excessively high levels).

In particular, the cage material must have sufficient strength and durability to withstand various conditions. First of all, the separator must not be torn or pierced due to the stresses that occur during battery assembly. Thus, the overall mechanical strength of the cage is an extremely important characteristic, in particular, determining the greater tensile strength of the material in both machine and transverse (i.e. at an angle) directions, and allows the manufacturer to handle such a cage with greater ease and without strict rules aimed at preventing the destruction of the structure of the separator or the deterioration of its performance during such a critical procedure as assembly. In addition, from a chemical point of view, the separator must withstand the oxidizing and reducing environment present directly inside the battery, in particular when it is fully charged. Any damage during use, in particular to structural strength, allowing excessive current flow or inter-electrode contact, may render the battery incapable of generating electricity and may render it completely inoperable. Thus, even having the above ability to withstand chemical contact, such a separator should also not lose dimensional stability (i.e. should not warp or melt) or mechanical strength during storage, manufacture and use for the same reasons indicated above.

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However, at the same time, the separator must be of the proper thickness as such to maintain the high energy densities and power of the battery itself. Uniform thickness is also very important to ensure long life, as any uneven wear on the separator prevents proper passage of the electrolyte and also increases the likelihood of electrode-to-electrode contact.

In all lithium-ion batteries, the electrolyte is unstable in the presence of a (carbonaceous) anode. For this reason, the electrolyte decomposes and forms a surface layer on the anode, called a solid electrolyte interfacial layer, which is formed on the surface of the anode from the decomposed and polymerized electrolyte. This layer prevents further decomposition of the electrolyte and is conductive to lithium ions, thus allowing the battery to be repeatedly charged and discharged.

With conventional lithium-ion separators, which have a pore size of 0.01 µm, or 10 nm, the formation of the SEI layer is slow due to the slow movement of the electrolyte towards the anode surface. Thus, the separator acts as a regulator of the formation of the SEI layer.

In industrial settings, manufacturers strive to speed up this process as quickly as possible, using the lowest current and lowest voltage to minimize the time and cost of this process and maximize equipment utilization.

In the case of non-woven separators whose pore size is greater than 10 nm, i. e. about 200-500 nm, the formation of the SEI layer does not depend on the pore size of the separator and is faster. In this case, a layer is formed that is uneven and leaves a large number of open spaces, i.e. does not fully protect the anode, resulting in the possibility of further decomposition. Thus, the process of forming the SEI layer for nonwoven separators takes more time, and the process itself depends on the strength of the electric current, and not on the pore size of the separator. In addition, some nonwoven separators are made of such a material and have such a porosity that the SEI layer can grow directly on nonwoven fibers, and the formation process must continue for a sufficient amount of time and requires sufficient current to allow this formation, which on nonwoven fibers can pass more slowly than on the electrodes.

One problem is that if a conventional forming process is used for lithium-ion batteries with a non-woven separator or any separator having a high porosity and increased pore size, the SEI layer is not completely formed and some areas of the anode still remain. open to electrolyte. If this happens when the cell is removed from the forming process (disconnected electrically), the SEI layer continues to build up and this process will absorb the charge of the cell. This continued formation of the SEI layer may be misinterpreted as a soft short circuit within the cell and may result in significant self-discharge until the cell is properly formed.

For batteries containing such a separator, the correct charge cycle must be used to create sufficient solid electrolyte interfacial layer (SEI) at the anode of the battery and also directly on the fibers of the separator. Such a cycle may include applying a first current to the battery during the first part of the cycle to properly deposit the electrolyte on the anode. In the second part of the cycle, a second current can be used. Also, during the initial formation of the solid electrolyte interfacial layer, high voltage impregnation may be required to achieve low initial self-discharge.

The standards currently in force today do not meet these critical limitations related to the deposition of a solid electrolyte interfacial layer. Thus, there is still a need to provide deposition parameters that provide sufficient solid electrolyte interfacial layer at the battery anode. At present, such a manufacturing method has not yet been explored to this extent in the field of battery separators. Also, an efficient, reasonably simple and easy battery manufacturing method that provides sufficient impregnation voltage and sufficient current to transport electrons and deposit an electrolyte is desirable in the field of rechargeable battery manufacturing; So far, this method has not been developed.

The essence of the invention

In view of the above disadvantages of known types of lithium ion batteries currently presented in the art, the present invention provides an improved lithium ion battery and a method for manufacturing the same, which overcomes the above disadvantages and disadvantages of the prior art. Also, the general object of the present invention, which is detailed below, is to provide a new and improved lithium ion battery and a method for its manufacture, which have all the advantages over the prior art described above, as well as many new features, resulting in a lithium ion battery which is not assumed, not made obvious, not suggested, or even implied by the prior art, either alone or in any combination of the foregoing.

A distinctive advantage of the present invention lies in the ease of fabrication of a lithium ion battery with an efficient and properly formed solid electrolyte interfacial layer. Another distinctive advantage of the present invention is that the current, and not the pore size of the separator, limits the rate of formation of the solid electrolyte interfacial layer. Another distinct advantage of the present invention is that the slow process and high voltage allow a uniform and complete coating of the battery anode to be made.

Lithium Iron Phosphate (LFP) cells have high charging speed characteristics, good cycle life and superior safety compared to other Lithium Ion batteries (LIB). They often compete with lead-acid batteries in applications such as e-bikes, backup and emergency power systems (UPS), powering light electric vehicles (electric forklifts, golf carts, etc.) and grid energy storage. In these applications, they have significant advantages in terms of cycle life, energy density and charge acceptance rate. However, they have disadvantages related to cost and safety. Converting these elements from polyolefin cages to Dreamweaver (DWI) Silver cages will increase both the safety and cost of the elements, making them more competitive in these markets. This change will also improve the performance of Lithium Iron Phosphate (LFP) cells in other applications such as power tools, electric buses, etc. where they are comparable to Nickel Metal Hydride (NiMH) or other Lithium Ion Batteries (LIB ).

However, some initial attempts at direct replacement resulted in high self-discharge after initial cell formation. These cells have performance equal to or better in all other respects, including cycle life, high temperature cycle life, discharge capacity at various charge rates up to 9C, and pass a full range of safety tests including thermal chamber (150-190°C), overload , short circuit and pierce with a nail. After multiple cycles, the cells also showed low self-discharge. Thus, it became apparent that there were differences in the initial life of the cell, and it made sense to investigate the formation of the SEI layer as a means to reduce the initial self-discharge of the cells.

Accordingly, the present invention relates to a method for manufacturing a lithium ion battery. The method includes the following steps: assembly of an element having an internal volume containing an anode, a cathode and a separator; filling the internal volume of the cell with electrolyte; connecting the anode and cathode to the charger; charging the cell at a charging rate that is less than or equal to C/6 until the cell reaches its maximum voltage; and charging the cell at a voltage that is higher than the specified voltage for more than 6 hours. The present invention also includes a method in which said voltage is greater than or equal to 3.4 V. The present invention also includes a method in which said voltage is greater than 3 .4 V.

Such a manufacturing method has not yet been explored in the prior art of a rechargeable battery, in particular, with respect to the ability to provide a sufficient solid electrolyte interfacial layer, which can reduce the self-discharge of a rechargeable battery. The use of current is particularly important so that specific parameters provide sufficient solid electrolyte interfacial layer such that the ideal applied current is no more than C/4, preferably no more than C/6, and more preferably no more than C/10 (where C is charge rate required to charge a cell to full capacity in one hour). In addition, the use of voltage is also very important, since specific parameters ensure that the solid electrolyte interfacial layer is sufficiently formed, so that the ideal voltage is greater than 3.3V, preferably 3.6V, and more preferably 3.9V. In addition, the use of current required to maintain a voltage greater than 3.6 V for a sufficient amount of time occurs for more than 6 hours, preferably more than 9 hours, more preferably more than 12 hours. This process allows the SEI layer to form at a rate that is limited current (but not the pore size of the separator), and also allows a slow process with high voltage, which continues to operate, to fill any gaps on the anode surface and achieve a uniform complete coverage of the anode.

In addition, it should be noted that although the present invention describes a single-layer separator containing microfibers and nanofibers, the use of multiple layers of such a fabric structure or one layer of the disclosed battery separator fabric with at least one other layer of a different type of fabric can also be applied in the present invention and fall within the scope of protection of the entire present invention described in this application.

Such battery separators as described herein are clearly suitable for upgrading known primary and rechargeable batteries, but can also be used for other forms of electrolyte conductive energy storage technologies such as capacitors, supercapacitors and ultracapacitors. Indeed, the control provided by the pore size of such separators according to the present invention can significantly reduce energy losses, increase energy efficiency and improve other characteristics of these devices.

In addition, such battery separators, which include forming the SEI layer directly on the fibers, have a reduced pore size necessary for good separation. Because the

The SEI layer is known to be conductive for lithium ions, separators with the SEI layer formed on them also have high ionic conductivity, necessary for fast and efficient charging and discharging of the device.

These and other aspects of the present invention, along with the various features of novelty that characterize the present invention, are defined in the appended claims, which are included in and form part of the present invention. For a better understanding of the present invention, its operational advantages and the specific problems solved by its use, reference is made to the accompanying drawings and text material, which describes embodiments of the present invention.

Brief description of the drawings

New features representing a characteristic of the disclosed subject matter of the present invention are set forth in the claims appended below. However, the disclosed subject matter of the present invention itself, as well as its preferred mode of use, its additional objects and advantages, will be better understood upon reading the following detailed description of an exemplary embodiment in conjunction with the accompanying drawings, in which FIG. 1 is a schematic representation of a solid electrolyte interfacial layer on a carbon-containing anode of a lithium-ion battery;

in fig. 2 and 3 are scanning electron microscope (SEM) micrographs at 1000 and 2000 gain levels of one potentially preferred embodiment of a microfiber/nanofiber nonwoven battery separator structure;

in fig. 4 and 5 show SEM micrographs taken at gain levels of 5000 and 10000 of another potentially preferred embodiment of the microfiber/nanofiber nonwoven battery separator structure of the present invention;

in fig. 6 is a graph showing a comparison of capacitance after self-discharge and open cell voltage after self-discharge for cells made with electrodes from manufacturer A;

in fig. 7 is a bar graph showing the effect of shaping parameter on cell capacity after shaping for cells from manufacturer A;

in fig. 8 is a bar graph showing the influence of the formation parameter on the residual capacity after self-discharge for cells made with electrodes from manufacturer A;

in fig. 9 is a graph showing the cross-correlation between initial charge time and self-discharge in lithium-ion batteries for cells made with electrodes from manufacturer A;

in fig. 10 is a graph showing a comparison of capacity (mAh) after self-discharge and voltage (V) after self-discharge for cells made with electrodes from manufacturer B;

in fig. 11 is a bar graph showing the effect of shaping parameter on cell capacitance after shaping for cells made with electrodes from manufacturer B;

in fig. 12 is a bar graph showing the effect of formation parameter on residual capacity after self-discharge for cells made with electrodes from manufacturer B;

in fig. 13 is a graph showing the cross-correlation between initial charge time and self-discharge in lithium-ion batteries for cells made with electrodes from manufacturer B;

in fig. 14 and 15 show SEM micrographs of a comparative prior art CELGARD® 2400 separator taken at a gain level of 15000 before and after disassembly of the lithium iron phosphate cell and showing no noticeable SEI layer formation on the separator;

in fig. 16 shows a SEM micrograph of a Dreamweaver Silver 25 separator taken at a gain of 5000 before being inserted into a lithium iron phosphate cell;

in fig. 17 and 18 show SEM micrographs of Dreamweaver Silver 25 separators taken at gain levels of 3000 and 5000 after disassembly of the lithium iron phosphate cell, showing significant SEI layer formation on the separator;

in fig. 19 is a graph showing 2 and 50 charge/discharge curves for Lithium Iron Phosphate cells cycled at 2.4 to 3.6V to compare cells made with CELGARD® 2400 and Dreamweaver Silver 25 separators. ;

in fig. 20 is a graph showing the capacity during the first 50 cycles of lithium iron phosphate cells cycled in 1C mode at voltages from 2.4 to 3.6 V, for comparison of cells made with the known CELGARD® 2400 separator and the Dreamweaver Silver 25 separator according to the present invention;

in fig. 21 is a graph showing the speed characteristics of similar elements in 1C, 2C and 4C modes, also for comparison of elements made with the known CELGARD® 2400 separator and the Dreamweaver Silver 25 separator according to the present invention;

- 4 039132 in FIG. 22 is an exploded view of a rechargeable lithium ion battery according to the present invention, which includes a battery separator according to the present invention.

Like reference numbers refer to like parts throughout the drawings.

Detailed description of the invention

All features of this invention and its preferred embodiments are described in detail below with reference to the accompanying, but not limiting, drawings and illustrative examples.

Definitions.

Solid electrolyte interfacial layer (SEI layer) - a layer of material formed on a carbon-containing anode as a result of electrolyte decomposition.

Shaping is the process used to create the SEI layer, generally defined by attaching a cell to a charger capable of controlling current and voltage and charging the cell according to a predetermined voltage and current profile.

A carbon-containing anode is an electrode capable of receiving lithium ions and including carbon-containing materials such as graphite, hard carbon, activated carbon, and others generally used in the manufacture of lithium-ion batteries. An anode in general is a coating on a conductive material that is used to propagate and collect electron current and is called a current collector. A common material for an anode current collector is copper foil.

The cathode is an electrode capable of receiving lithium ions, which generally comprise lithium oxide compositions such as lithium iron phosphate, lithium carbonate, manganese nickel carbonate, and other compositions generally used in the art. In other cases, compositions based on sulfur, spinels, lithium manganese oxide and other compositions known in the art can be used. Cathodes in general also have a current collector, which in modern practice is aluminum foil.

An electrolyte is a liquid in which lithium salts can be dissolved and is used to transport lithium ions from the anode to the cathode. Examples include ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, mixtures of all of the above and others. The electrolytes may also contain additives, and in particular additives to facilitate the formation of the SEI layer.

C-parameter - is determined by the current required to charge the cell to full capacity. 1C is the charging rate at which the required current is sufficient to charge the cell to full capacity in one hour and which is generally equal to the cell's capacity C divided by one hour. Thus, for a cell with a capacity of 1 Ah, the charging current at a rate of 1C is 1A. A 2C charge rate corresponds to twice that current, and a 0.5C charge rate corresponds to half that current.

Manufacturing of microfibers and nanofibers.

As indicated above, the microfiber can be made from any polymer (or mixture of polymers) that has suitable chemical resistance and heat resistance to match the internal conditions of the element, as well as the ability to form suitable fibrous structures within the indicated ranges. Such fibers may also have the potential to withstand fibrillation or the like to increase the surface area of the fibers themselves to facilitate entanglement during nonwoven fabrication. Such fibers can be made by well-known fiber manufacturing methods such as melt spinning, wet spinning, solution spinning, melt blowing, and the like. In addition, such fibers can start as bicomponent fibers and have a size and/or shape that is reduced or changed during further processing to obtain such fibers as fibers of the segmented pie type (splittable pie fibers), island-in-the-sea fibers (islands-in -the-sea), etc. Such fibers may be cut into appropriate lengths for further processing, which may be less than 50 mm, or less than 25 mm, or even less than 12 mm. Such fibers may also be extended in length to provide improved processability or increased strength more suitable for lengths greater than 0.5 mm, greater than 1 mm, or even greater than 2 mm. Such fibers can also be fibrillated into downsized fibers or fibers which preferably form wet-spun nonwovens.

The nanofibers for use in the present invention can be made according to various well-known technologies such as islands in the sea, centrifugal spinning, electrospinning, film or fiber fibrillation, and the like. Companies such as Teijin and Hills supply potentially preferred island-in-the-sea type nanofibers (Teijin's nanofibers are supplied as PET NanoFront fibers 500-700 nm in diameter). Companies such as Dienes and FiberRio supply equipment for making nanofibers using centrifugal spinning technology. Xanofi supplies fibers and equipment for its manufacture using high shear liquid dispersion technology. Nanofiber-shaped polyaramids manufactured by DuPont show excellent heat resistance as well as other particularly advantageous properties.

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The production of nanofibers by electrospinning is carried out by DuPont, ESpin Technologies or using equipment supplied for this purpose by Elmarco. Nanofibers fibrillated from films are disclosed in US Pat. Nos. 6,110,588; 6432347 and 6432532, which are incorporated herein by reference in their entirety. Nanofibers fibrillated from other fibers can be made by high shear abrasive processing. Nanofibers made from fibrillated cellulose and polyacrylonitrile fibers are available from Engineered Fiber Technologies under the brand name EFTEC™. Any such nanofibers can also be cut and slurried at high shear to separate the fibers and allow them to be wet-laid into a nonwoven fabric. This high shear treatment can be carried out with or without the necessary microfibers.

Fibrillated nanofibers generally have a cross-sectional aspect ratio (ratio of the length of short fibers to their diameter) that is different from fibers originally made as nanofibers in a typical manner (eg, island-in-the-sea technology). One such transverse aspect ratio is described in detail in US Pat. No. 6,110,588, which is incorporated herein by reference in its entirety. Also in one preferred embodiment, the nanofibers have a cross aspect ratio greater than 1.5:1, preferably greater than 3.0:1, more preferably greater than 5.0:1.

Also acrylic, polyester, cellulose and polyolefin fibers are particularly preferred for this purpose, with fibrillated acrylic and cellulose fibers being potentially the most preferred. However, again, this is offered solely as an indication of the potentially preferred type of polymer for this purpose and is not intended to limit the scope of protection for possible polymeric materials or polymer blends used for this purpose.

In FIG. 1 schematically shows a solid electrolyte interfacial layer formed on a carbon-containing anode of a lithium-ion battery.

In lithium ion batteries, the electrolyte is unstable in the presence of an anode (carbon anode). Because of this, the electrolyte decomposes and forms a surface layer on the anode, called a solid electrolyte interfacial layer, which is formed on the anode surface from the decomposed and polymerized electrolyte. This layer also prevents electrolyte degradation and is conductive to lithium ions, thus allowing the battery to be repeatedly charged and discharged.

In the case of conventional lithium ion separators with a pore size of 0.01 µm, or 10 nm, the formation of the SEI layer is slow due to the slow movement of the electrolyte towards the anode surface. Thus, the separator acts as a regulator of the formation of the SEI layer.

In an industrial setting, manufacturers try to run this process as quickly as possible, using the lowest current and lowest voltage to minimize the time and cost associated with this process and maximize equipment utilization.

In the case of non-woven separators, which have a pore size greater than 10 nm, and more often of the order of 200-500 nm, the formation of the SEI layer does not depend on the pore size of the separator and is faster. In this case, a layer is formed that is uneven, more open and does not completely protect the anode, allowing further decomposition to occur. Thus, for the formation of the SEI layer in the case of separators made of nonwoven materials, more time is required.

One problem is that if a conventional lithium ion battery formation process with a non-woven separator or some other separator having high porosity and large pore size is used, the SEI layer is not completely formed and the anode regions are still exposed to the electrolyte. If this happens when the cell is removed from the formation process (disconnected electrically), the SEI layer continues to form and the cell's charge is consumed in this process. Such continued formation of the SEI layer can be misinterpreted as a soft short circuit (soft short) inside the cell and can lead to rapid self-discharge until the cell is not properly formed.

One potentially preferred embodiment of the original combination of microfiber and nanofibers is EFTEC™ A-010-4 fibrillated polyacrylonitrile fibers (FIGS. 2 and 3), which have a high amount of nanofibers as well as residual microfibers. The resulting nanofibers present in this combination are the result of fibrillation of the original microfibers. Nonwoven sheets made from these materials are shown in FIG. 2 and 3. For example, these fibers can be used as a base material to which additional microfibers or additional nanofibers can be added to control the pore size and other properties of the nonwoven, or such material can be used directly as a battery nonwoven separator. . Examples of such sheets with additional microfibers added are shown in FIG. 4 and 5. Typical properties of acrylic micro/nanofibers are shown in Table 1 below. one.

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Table 1

Acrylic Micro/Nanofiber Properties Density, g / cm ³ 1.17 Tensile strength, MPa Modulus of elasticity, GPa Elongation, % Typical fiber length, mm Freeness of the mass according to the Canadian standard, ml 450 6.0 fifteen 4.5-6.5 10-700 BET specific surface area (according to the Brunauer-Emmett-Teller method), m ² /g fifty Equilibrium humidity, % <2.0 Surface charge anionic

Another potentially preferred embodiment of the original combination of microfibers and nanofibers is EFTEC™ L-010-4 fibrillated cellulose fibers (FIGS. 2 and 3), which have a high amount of nanofibers as well as residual microfibers. The resulting nanofibers present in this combination are the result of fibrillation of the original microfibers. For example, these fibers can be used as a base material to which additional microfibers or additional nanofibers can be added to control the pore size and other properties of the nonwoven material, or such material can be directly used as a battery nonwoven separator.

Such fibers are substantially present, as described above, in the slurry composition, thus facilitating their incorporation into a nonwoven wet-spinning circuit.

Method for the manufacture of non-woven materials.

Combinations of materials are evaluated below to provide various concentrations of both components prior to their joint introduction into the wet molding process. Handcast sheets can be made using the TAPPI test method T-205, which is incorporated herein by reference in its entirety (this method basically, as described above, involves mixing them in a very high concentration and high shear rate aqueous solvent formulation). , which is commonly used in wet spinning fabrication and is described as refining the fibers, and finally laying the wet structure on a flat surface to evaporate the solvent).

The similarity of the nonwoven fabric structures in FIG. 4 and 5 (larger microfibers and smaller nanofibers) is evident, and the reduced amount of nanofibers in these structures is also evident in these micrographs.

The method of manufacturing and forming the element, as presented in table. 3 includes the following steps:

Drying the separator to remove residual water in an air dryer, convection dryer, forced air dryer, vacuum dryer, or other dryer known in the art. This step is less necessary and also has temperature limitations for polyolefin cages. In the case of a non-woven separator, residual water can be removed from the hand-laid sheets by drying in an oven for 1 hour at 100°C. More preferably, such drying should be continued for 3 hours, or most preferably for 12 hours. A temperature of 110°C is more preferred, and a temperature of 130°C is most preferred. For material in rolls, the time and temperature required may depend on the size and placement of the roll, but in general a drying time of 12 hours at 100°C may be sufficient. However, a temperature of 110°C may be more preferable for drying, and a temperature of 130°C may be most preferred. In addition, a drying time of 24 hours may be preferred to remove residual moisture, and a drying time of 48 hours is most preferred.

Assembly of elements.

The assembly can be performed according to any known method and for any shape of the element. The procedures may include winding, bundling, laminating, or other operations. Element formats can include cylindrical elements of various shapes and sizes well known in the art, as well as polymer elements and prismatic elements, both of which can also have shapes and sizes well known in the art.

Drying items.

In some cases, to remove the last residual moisture from the anode, cathode, and separator, the cell is dried, which can be done in an air oven, convection oven, forced air oven, or vacuum oven. This can be done at a temperature of 100°C or higher, for example preferably 110°C and most preferably 130°C.

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Filling cells with electrolyte.

Filling can be done by any method suitable for delivering the electrolyte to the interior of the cell, and a variety of methods are well known in the art. The electrolyte may be any electrolyte suitable for a lithium ion battery that generally contains a mixture of organic solvents as well as a lithium salt and counterions (exchangeable ions). Examples of organic solvents include ethylene carbonate, methylene carbonate, diethyl carbonate, dimethyl carbonate and propylene carbonate. An example of a lithium salt is LiPF ₆ . In yet another embodiment, ionic liquids can be used that provide benefits such as increased heat resistance and high electrical strength.

Formation.

Thereafter, the assembled and filled cells must go through an initial charging process to form the SEI layer and charge the cells. Such formation includes various charging steps, which can be defined by their current and voltage profile, as described above. This shaping current and voltage profile may contain pauses at various points in the charging profile during which a constant voltage or a floating voltage may be applied. The use of current is particularly important because the specific parameters ensure that sufficient solid electrolyte interfacial layer is created so that the ideal applied current should be no more than C/4, preferably no more than C/6 and more preferably no more than C/10 (where C is the speed required to charge the cell to full capacity in one hour). In addition, the use of voltage is also very important, since specific parameters ensure that the solid electrolyte interfacial layer is sufficiently formed, so that the ideal voltage is greater than 3.3V, preferably 3.6V, and more preferably 3.9V. In addition, the use of current required to maintain a voltage greater than 3.6 V for a sufficient amount of time occurs for more than 6 hours, preferably more than 9 hours, more preferably more than 12 hours. This process allows the SEI layer to form at a rate that is limited current (but not the pore size of the separator), and also allows a slow process at high voltage, which continues to act to fill any gaps on the anode surface and achieve uniform complete coverage of the anode.

The elements formed in this process also differ in that the SEI layer is formed directly on the separator and not only on the anode, which is not the case with known polyolefin separators. This is clearly seen in the known polyolefin cages shown in FIG. 14 and 15 showing the CELGARD® 2400 separator before insertion into the cell and after 29 cycles in an LFP (Lithium Iron Phosphate Cell, (LiFePO4)) cell. In the case of nonwoven separators, the SEI layer may be formed under conditions suitable for forming the layer directly on the separator, as may be apparent from the comparison between FIGS. 16 showing the separator before placement in the element, and FIG. 17 and 18 showing the separator after 29 cycles in the LFP element and clearly showing the SEI layer formed on the separator. As shown by the charge-discharge curves in FIG. 19, the cyclic resource shown in FIG. 20 and the speed characteristics shown in FIG. 21, even with the SEI layer directly on the separator, the conductivity of the separator and electrolyte and the SEI layer is higher than CELGARD® 2400 brand separators, resulting in higher discharge capacity, reduced cycling degradation and higher speed performance.

The creation of an SEI layer on a separator can take various forms. As such, the SEI layer can be seen in SEM micrographs (scanning electron microscope micrographs) including areas in which substantially all of the pores present in the SEM micrographs of the original separator are filled. The SEI layer may also contain areas in which the nanofibers present in the SEM micrographs of the original separator are not observed because they are embedded in the SEI layer. The SEI layer of a lithium ion cell is known to be made from a decomposed electrolyte and therefore contains the lithium salt used in their manufacture, containing a large amount of fluorine and phosphorus, which can be measured using energy dispersive X-ray spectroscopy, or EDS. Such separators may contain areas that have a phosphorus level, measured using EDS, greater than 1.5%, preferably greater than 2.0%, more preferably greater than 2.5%. Such separators may also contain areas that have a fluorine level, measured using EDS, greater than 5%, preferably greater than 7%, more preferably greater than 9%.

Examples

The Dreamweaver Silver separator is made in the manner described in US Pat. No. 8,936,878, which is incorporated herein by reference in its entirety. Examples used in these tests are a Dreamweaver Silver 25 separator containing EFTec A-010-04 nanofibrillated polyacrylonitrile fibers, EFTec L-010-04 nanofibrillated cellulose fibers, and 5 mm polyethylene terephthalate fibers 0.3 denier. on a continuous elementary fiber. The characteristics of this separator are given in table. 2 below.

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table 2

Main properties of the membrane unit of measurement Dreamweaver Silver™ 25 Thickness (at 12.6 psi) micron 27 Thickness (at 25 psi) micron 26 Air permeability Gurley (JIS) sec 80 Porosity % 56% Pore size micron 1.1 Shrinkage in cross section direction @ 160 C % 0 Shrinkage in the machine direction @ 160 C % 2 Strength in the transverse direction kgf / cm ² 175 Strength in the machine direction kgf / cm ² 330 Young's modulus kgf / cm ² 23000 The temperature of preservation of mechanical integrity during melting °C 300 Puncture resistance G 280 Moisture contents % 3.7%

The thickness of the fabric was measured and then the fabric was cut into pieces of suitable sizes and shapes to be placed inside the lithium ion cells of the rechargeable battery. However, prior to such placement, battery separator fabric samples were examined and tested for various properties regarding their ability to function as suitable battery separators. In addition, comparative examples of nanofiber membranes for a battery separator according to US Pat. literature about CELGARD products.

Basic analysis and test of the battery separator.

Below are the following test reports:

The porosity was calculated according to the method described in US Pat. No. 7,112,389, which is incorporated herein by reference in its entirety. The results are presented in %, which refer to the portion of the mass of the separator that is filled with air or non-solid materials such as electrolyte when the separator is in the battery.

The Gurley air permeability was measured according to the TAPPI test method T460, which is incorporated herein by reference in its entirety. The Gurley densimeter model 4110 was used as the measuring instrument for this test. For the test, the sample was introduced and fixed in the densimeter. The cylinder was raised to the line 100 cm ³ (100 ml) and then allowed to fall under its own weight. The time (in seconds) required for 100 cm ^{3 of} air to pass through the sample was recorded. The results are reported in seconds/100 cm ³ which is the time required for 100 cm ^{3 of} air to pass through the separator.

The mean effective pore size was determined in accordance with the Standard Test Method for Pore Size Characterization of Membrane Filters using an automated liquid porosimeter according to ASTM E-1294, which uses an automated method based on the initial boiling point according to ASTM F 316 using capillary flow porosimeter. Tests were performed by Porous Materials, Inc., Ithaca, New York.

The air permeability of the separator was determined by measuring the time required to pass a fixed volume of air through a standard area under light pressure. The procedure is described in ASTM D-726-58.

Experimental part: the manufacturer of the A element.

Commercial lithium iron phosphate electrodes were obtained from two manufacturers and tested in single layer stacks sandwiched between two plexiglass pieces to create a uniform pressure. In the cells, the electrical characteristics beyond self-discharge were remarkably constant, as will be described more fully in another section.

Single-layer packet elements had a size of 50x50 mm. The electrodes (matched pairs of anode and cathode) were made by commercial battery manufacturers in China. The cells were filled with lithium-ion battery electrolyte containing 1 mol of LiPF ₆ in a mixture of ethylene carbonate, dimethyl

- 9 039132 carbonate and diethyl carbonate with a volume ratio of 4:3:3, hermetically sealed and tested according to the procedure and test parameters shown in table. 3, using the parameters specified in table. 4 below (in particular, charge rate, voltage, cut-off current and number of SEI formation cycles, and separator drying temperature for each cell). The test was performed on a Neware battery tester using the procedures listed below.

The cell fabrication process included separator drying, cell assembly and drying, electrolyte filling and shaping followed by a self-discharge test at 30% state of charge (SoC), and a final capacity test including full charge and full discharge. The results of these tests are given in table. 3 and 4 below.

Table 3

Element cycle

The separator is dried for 3 hours under vacuum at the drying temperature T.

Collect elements.

Dry the elements overnight at 100°C.

Fill cells with electrolyte, wait >2 hours.

Perform a test charge (Tap charge) up to 2.00 V.

I Withstand at a constant voltage (CV) of 2 V for 2 hours.

Wait 24 hours (voltage off (rest)).

Carry out shaping by charging in constant current mode (CC rate) to rated voltage, then in constant voltage mode (CV) until voltage cutoff (CV Cutoff).

Discharge in constant current mode (CC rate) to a voltage of 2.50 V.

Perform 2nd charging formation if necessary.

Perform a 2nd discharge if necessary.

Charge cells at C/6 rate to 30% state of charge™ (SoC).

Record the voltage (after a 24 hour soak period).

Wait 14 days.

Record the voltage.

Discharge at a rate of C / 6 to a voltage of 2.50 V.

The cells are charged at a rate of C/6 to a voltage of 3.60 V, then in constant voltage (CV) mode until a current of C/60 is reached.

The cells are discharged at a rate of C / 6 to a voltage of 2.50 V.

Charge cells to 50% state of charge (SoC) at C/6 rate.

Deliver items to DWI (Dreamweaver International).

Table 4

Element A Element B DC charging rate (CC rate) Voltage Constant voltage cutoff (CV Cutoff). Quantity cycles Temperature drying A1 IN 1 S/b 3.6 C/60 2 120 A2 IN 2 C/6 3.6 C/60 120 AZ VZ C/6 3.6 C/30 2 120 A4 AT 4 C/3 3.6 C/30 2 120 A5 AT 5 C/3 3.6 C/30 one 120 Ab wb C/6 3.4 C/60 2 120 A7 AT 7 C/6 3.6 C/60 2 ON A8 AT 8 C/6 3.6 C/60 one 110 A9 AT 9 C/6 3.6 C/30 2 110 AYu AT 10 O'CLOCK C/3 3.6 C/30 2 ON AP AT 11 C/3 3.6 C/30 one ON A12 AT 12 C/6 3.4 C/60 2 ON

The results of the formation of elements made from electrodes from manufacturer A (as indicated above) are shown below in table. 5. It can be seen from the table that the state of each element is the average of the two elements.

- 10 039132

Table 5

Element 1st cycle Coulomb efficiency 1st cycle Charging time 2nd cycle Coulomb efficiency 2nd cycle Charging time A1 68% 12:05:30 101.7% 7:09 A2 45% 42:55:30 AZ 84% 7:45:00 100.1% 5:42 A4 75% 10:25:30 101.6% 5:57 A5 81% 8:02:00 Ab 84% 09:01:00 97.6% 7:08 A7 76% 12:18:00 102.7% 6:12 A8 fifty% 42:06:30 A9 83% 9:11:00 am 100.7% 6:19 A10 76% 08:59:00 100.0% 5:59 AN 57% 14:52:30 A12 81% 09:07:00 98.3% 6:28

Several conclusions can be drawn from these results. The Coulomb efficiency in the first charge cycle is relatively low and ranges from 45% for the A2 state to 84% for the A3 and A6 states, with the Coulomb efficiency greater than 80% for the A5, A9 and A12 states. The duration of the charging cycle correlates with the Coulomb efficiency in a huge range from 8:02 to 42:55 hours. These extremely long periods are observed in cells that have undergone only one charge (A2, A8, A11). The variations between the elements in these pairs are very large, indicating a potential error in the experiment. The Coulomb efficiency in the 2nd cycle for the elements for which it was determined is very close to 100% for all elements and ranges from 97.6 to 102.7%. The average discrepancy between pairs of elements was 0.75%. The charging time in the 2nd cycle is also relatively uniform, ranging only from 5:42 to 7:09 h. The average deviation between cell pairs was 0:30 h, indicating a very close correlation of values.

The results of the self-discharge test, including discharge after self-discharge, are shown in table. 6 below, as well as in FIG. 6. In addition, it is observed that each state of an element is the average of two elements.

Table 6

Element self-discharge Day 1 self-discharge Day 2 Losses due to self-discharge, V Residual capacity after self-discharge, mAh Losses due to self-discharge, mAh Final discharge capacity A1 3.293 3.263 0.030 14.1 3.9 55.4 A2 3.295 3.281 0.014 15.7 2.3 57.0 AZ 3.298 3.258 0.040 13.5 4.5 54.6 A4 3.290 3.258 0.032 14.0 4.0 56.1 A5 3.295 3.268 0.027 13.6 4.4 52.8 Ab 3.292 3.264 0.028 12.2 5.8 50.5 A7 3.290 3.264 0.026 14.6 3.4 54.9 A8 3.297 3.280 0.017 17.8 0.2 56.5 A9 3.285 3.252 0.033 13.0 5.0 58.9 A10 3.288 3.254 0.034 12.9 5.1 56.7 AN 3.295 3.267 0.029 15.9 2.1 55.6 A12 3.294 3.266 0.029 13.4 4.6 51.4

Again, several conclusions can be drawn. The range of losses due to self-discharge, both in terms of voltage and in terms of capacitance, is very wide. The voltage loss ranges from 14 to 40 mV and the capacitance loss ranges from 0.2 to 5.8 mAh. From FIG. 6, it can be concluded that there is only a weak correlation between the end voltage of self-discharge, voltage losses due to self-discharge, and capacitance losses due to self-discharge. In addition, the range of the final discharge capacity is wide, but the correlation with the process parameters is only small. There is likely to be a large experimental error due to both the small size of the electrodes and the potential mismatch. There is no strong correlation between the pairs, with the average deviation in pairs being greater than 2 mAh.

Data analysis: cell manufacturer A.

For a quasi-designed experiment, a data set was formed that allows averaging partial sets to isolate a single parameter and obtain a change in various measurements related to this parameter. These averages and isolated parameters are shown in Table 1 below. 7.

- 11 039132

Table 7

Parameter Group #1 Group #2 Drying temperature Al, A2, AZ, A4, A5, Ab A7, A8, A9, A10, All, A12 Charging speed DC (CCC Rate) A1, A2, A7, A8 A4, A5, A1 0, All DC Current Cutoff (CVC Cutoff) Al, A7 AZ, A9 Shutdown by charging voltage (CV Cutoff) Al, A7 Ab, A12 Cycle numbers A2, A5, A8, AN A1, A4, A7, A10

Averaging the data in each of these groups provides the ability to isolate the parameter in the largest group of samples, averaging the experimental error, and also allows the identification of first-level cross-correlations. In each case, the minimum number of average elements is 8 (for current trip at constant voltage and voltage trip at charging). The average values obtained for each measurement are shown below in table. eight.

Table 8

C1 Efficiency C1 Time C2 Efficiency S2 Time self-discharge Day 1 self-discharge Day 14 Self-discharge loss, V Self-discharge losses, mAh Final charging capacity Final discharge capacity Drying temperature 110°С 71% 16:05:40 100.4% 6:14 3.291 3.264 0.028 3.4 56.1 55.7 120°C 73% 15:02:25 100.3% 6:29 3.294 3.265 0.029 4.1 56.0 54.4 Charging in constant current mode (CC rate) S/b 60% 27:21:23 102.2% 6:41 3.294 3.272 0.022 2.4 56.4 56.0 C/3 72% 10:34:45 100.8% 5:58 3.292 3.261 0.030 3.9 55.8 55.3 Charging in constant voltage mode until voltage cutoff (CV Cutoff) C/60 72% 12:11:45 102.2% 6:41 3.291 3.263 0.028 3.7 55.7 55.1 C/30 84% 8:28:00 100.4% 6:00 3.292 3.255 0.037 4.8 57.2 56.8 Voltage 3.6 72% 12:11:45 102.2% 6:41 3.291 3.263 0.028 3.7 55.7 55.1 3.4 83% 09:04:00 97.9% 6:48 3.293 3.259 0.031 4.1 56.3 55.8 Cycles 1 cycle 59% 26:59:08 3.295 3.274 0.022 2.2 55.9 55.5 2 Cycles 74% 10:57:00 24:21:37 6:19 3.290 3.259 0.031 4.1 56.3 55.8

From these data, the specialist understands that the result (element in the table) varies depending on the parameter (leftmost column of the table). Among the results, two results are important to the user of the element as performance indicators. The first of these is self-discharge, which is identified with losses due to self-discharge in mAh, i.e. the actual capacity lost during the 14 day soak period. The second important indicator is the final discharge capacity, which can be represented as the initial capacity of a cell ready for sale. With regard to the charging capacity, some conclusions can be drawn.

The final discharge capacity is positively affected by a decrease in the drying temperature and an increase in the critical charging voltage (disconnect voltage during charging), each of these parameters affecting the capacity within 3-4 mAh or 5-7%. These relationships are shown in Fig. 7. In addition, self-discharge losses (in mAh) are positively affected (reduced) by most of the parameters, as shown in FIG. 8, including reduced drying temperature, reduced DC charging rate, reduced DC charging cutoff current, increased charging voltage, and reduced number of cycles (which looks like an experimental anomaly because the Coulomb efficiency of these cells does not correlate with the Coulomb efficiency of the first cycle of cells subjected to two processing cycles). These results are the only basis for the present invention, which includes a shaping cycle using reduced current, increased voltage, and continuous impregnation at high voltage, which in this case corresponds to a reduced cutoff current during DC charging.

In FIG. 9 is a table showing the cross-correlation between initial charge time and self-discharge in lithium ion batteries. The strongest correlation between the total time spent in the initial charge cycle and the remaining capacity after self-discharge after 14 days on an open cell is shown on the right side of the chart. Based on conditions

- 12 039132 capacitance loss can be reduced by more than 50%, i.e. 5 mV to less than 2.5 mV (in cells charged to 18 mV or at 30% state of charge before self-discharge). In general, it can be noted that there seems to be a strong correlation with the use of longer initial charge periods to reduce self-discharge at the end of formation, regardless of the parameters used to achieve improved charge times.

Experimental part: manufacturer B of the element.

The results of the formation of elements made of electrodes from manufacturer B are shown below in table. 9. The state of each element is represented by the average of the states of the two elements.

Table 9

Element 1st cycle Coulomb efficiency 1st cycle Charging time 2nd cycle Coulomb efficiency 2nd cycle Charging time IN 1 53% 17:16:00 99.7% 7:10 IN 2 82% 09:04:30 vz 35% 22:11:00 99.2% 6:34 AT 4 46% 15:16:30 100.7% 6:51 AT 5 34% 24:44:00 wb 82% 14:13:30 100.0% 7:18 AT 7 41% 30:34:30 75.5% 13:33 AT 8 60% 14:58:30 AT 9 17% 45:29:30 99.4% 7:19 AT 10 O'CLOCK 56% 18:32:30 75.5% 10:03 AT 11 84% 8:46:00 AT 12 85% 10:50:00 98.8% 7:56

Several conclusions can be drawn from these results, which are similar to those for manufacturer A. The Coulomb efficiency for the first charge cycle is relatively low and ranges from 13% for condition B8 to 85% for condition B12, with conditions B2, B6 and B11 Coulomb efficiency is greater than 80%. The duration of the charge cycle correlates with the Coulomb efficiency over a huge range of charge times from 8:46 to 45:29 h. There does not appear to be a correlation between long charge times and formation states, in contrast to manufacturer A. Some pairs show good compatibility, while as other pairs have a large spread, which indicates an irregular error in the experiment. The Coulomb efficiency for the 2nd cycle, if it has been determined, is very close to 100% for all elements, except for two elements (B7-2, E10-1), for which it is in the range from 98.8 to 100.7% . The charging time for the 2nd cycle is also relatively uniform and ranges from 6:34 to 13:33 hours.

The results of the self-discharge test, including the discharge after self-discharge, are presented in table. 10. Again, each element state is the average of the states of the two elements.

Table 10

Element self-discharge Day 1 self-discharge Day 2 Losses due to self-discharge, V Residual capacity after self-discharge, mAh Losses due to self-discharge, mAh Final discharge capacity IN 1 3.291 3.249 0.042 13.7 4.3 58.0 IN 2 3.290 3.239 0.051 11.8 6.2 57.0 vz 3,300 3.254 0.046 12.5 5.5 57.3 AT 4 3.295 3.248 0.047 12.4 5.6 60.6 AT 5 3.299 3.262 0.037 15.1 2.9 62.1 wb 3.290 3.248 0.043 12.1 5.9 63.5 AT 7 3.295 3.256 0.039 13.8 4.2 61.8 AT 8 3.295 3.254 0.042 13.4 4.6 62.2 AT 9 3.292 3.251 0.041 12.6 5.4 66.3 AT 10 O'CLOCK 3.282 3.246 0.037 12.3 5.7 61.6 AT 11 3.280 3.227 0.053 10.3 7.7 63.3 AT 12 3.287 3.249 0.039 12.1 5.9 55.1

Again, several conclusions can be drawn. The range of losses due to self-discharge, both in terms of voltage and in terms of capacitance, is very wide. The voltage loss ranges from 37 to 86 mV and the capacitance loss ranges from 2.9 to 7.7 mAh. There is a good correlation between the end voltage of self-discharge, voltage losses due to self-discharge, and capacitance loss after self-discharge (as shown in Fig. 10). The range of the final discharge capacity is large, but the correlation with the process parameters is only small. Apparently, in this case there is a large error in the experiment, both because of the small size of the electrodes and because of the potential mismatch. There is no strong correlation between the pairs, with the average deviation in the pairs being greater than 2 mAh.

Data analysis: manufacturer B elements.

The data were averaged over the same groups as for manufacturer B. The average values obtained for each measurement are shown in Table 1 below. eleven.

Table 11

C1 Efficiency C1 Time C2 Efficiency S2 Time self-discharge Day 1 self-discharge Day 14 Self-discharge loss, V Self-discharge losses, mAh Final charging capacity Final discharge capacity Drying temperature 110°С 57% 21:31:50 87.3% 9:43 3.288 3.247 0.041 5.6 61.3 60.3 120°C 57% 16:40:00 100.0% 7:02 3.310 3.220 0.091 6.4 60.2 59.1 Charging in constant current mode (CC rate) C/6 65% 17:49:37 94% 9:00 3.291 3.249 0.037 5.1 61.0 59.9 C/3 55% 16:49:45 88% 8:27 3.294 3.190 oh yuh 7.1 61.8 60.8 Charging in constant voltage mode until voltage cutoff (CV Cutoff). C/60 47% 23:55:15 88% 10:21 3.293 3.252 0.041 4.3 60.6 59.6 C/30 23% 37:43:20 99% 7:04 3.335 3.272 0.063 5.5 62.1 61.2 Voltage 3.6 54% 23:22:30 89% 10:18 3.294 3.254 0.030 4.3 60.6 59.6 3.4 83% 12:31:45 99% 7:37 3.289 3.248 0.041 5.9 59.3 57.8 Cycles 1 cycle 65% 14:23:15 3.296 3.190 0.106 7.0 61.1 60.2 2 Cycles 49% 20:24:52 88% 9:24 3.291 3,250 0.041 5.1 60.8 59.9

When considering these data, as with manufacturer A, some conclusions can be drawn. The final discharge capacity is quite suitable and really only depends on the charging voltage. These relationships are shown in Fig. 11. Losses due to self-discharge (in mAh) depend positively (reduced) on most of the parameters, as shown in FIG. 12, including lowering the drying temperature, lowering the charging speed in constant current mode, reducing the cutoff current in constant current charging, increasing the charging voltage, and increasing the number of cycles. Again, these results support the conclusion that slow charging to high voltage with increasing soak time at high voltage results in superior battery performance.

In particular, with regard to self-discharge, the correlations are the same as for manufacturer A, except for the number of cycles, which for manufacturer A seems to be an experimental anomaly due to the inconsistency of the Coulomb efficiency in the first cycle between cells that have undergone one cycle of formation, and cells that have undergone two cycles of formation, cells from manufacturer B do not have such inconsistency, and thus the conclusion is that increasing the number of cycles contributes to a decrease in self-discharge, which is consistent with the general idea of many other manufactured cells.

As with manufacturer A, there is one significant cross-correlation between C1 time and self-discharge loss, which is shown below in FIG. 13. As shown in the figure, there appears to be a strong correlation with the use of longer initial charge periods to reduce self-discharge at the end of formation, independent of the parameters used to achieve improved charge times.

Several strong correlations are observed between shaping parameters and self-discharge and achieved cell capacity. While each cell must be optimized individually and these results may not correlate with similar results for other cells, the following recommendations are most likely to result in cell capacity improvements of up to 5% and self-discharge rates of up to 50% less. %.

Based on these results, it is recommended that, in specific embodiments, the Dreamweaver Silver Separator be dried at a maximum drying temperature of 110°C. It is also recommended that a low initial charge cycle current of maximum C/6 be used to form the SEI layer until the cell is partially charged, and a higher charge current of C/6 after the cell is partially charged. . It is also recommended that shaping occur until at least 3.6 V is reached, or even greater than 4.0 V or higher for some cathode systems. It is also recommended that shaping include high constant voltage (CV) charging either until a low current (less than C/60) is reached or for a specified amount of time (greater than 6 hours).

In FIG. 22 shows a typical structure of a battery 10 with an outer casing 12 that contains the remaining components and is securely sealed to prevent environmental contamination that may enter the cell, as well as any leakage of electrolyte from the cell. So the anode

- 14 039132 is located parallel to the cathode 16 with at least one battery separator 18 between them. Electrolyte 20 is added to the cell prior to sealing to provide the necessary ion generation. Thus, the separator 18 helps to prevent contact of the anode 14 with the cathode 16, and also allows the selective migration of ions through it from the electrolyte 20. The general shape of the cell is defined by the present description of its design, but with different sizes of structures and designs of each internal component depending on the size and the design of the element itself. In this case, in order to properly test the effectiveness of the separator located inside such a cell, a button battery was made of essentially round solid components.

In this regard, tablet-type elements were made for disassembly and measurement of the separator after disassembly. Tablet-type elements of brand CR2032 were assembled. Lithium iron phosphate cell (LFP, LiFePO ₄ ) and graphite electrode were used commercial electrodes from manufacturer B above, and a 1.0 M solution of LiPF ₆ in a mixture of ethylene carbonate and diethyl carbonate was used as electrolyte (EC/DEC, 1: 1 by volume). The CELGARD 2400 separator was used after drying at 60°C. To test the DWI Silver separator, the elements were made with a non-dried separator, as well as a separator that was dried for 4 hours at a temperature of 90 and 120°C. After assembly, the elements were kept under vacuum at a temperature of 50°C overnight to stabilize. After stabilization, the cells were cycled (charged and discharged in constant current and constant voltage, CCCV modes) using a battery tester from Toyo. Initially, the elements were cyclically processed for 2 cycles of formation, followed by a test of speed characteristics in modes 1C, 2C, 4C, 2C (3 cyclic treatments in each mode). After testing the speed characteristics, the cells were cyclically processed for 50 cycles at a charging rate of 1C. The results of these cycling tests are shown in the form of charge-discharge curves in FIG. 19 while the cyclic resource is shown in FIG. 20 and the speed characteristics are shown in FIG. 21.

As shown in FIG. 20, such a battery with a pre-formed SEI layer with a tangled microfiber/nano-fiber separator (e.g., DWI Silver 25), which is present during this formation of the SEI layer and contains ethylene carbonate/diethylene carbonate and LiPF ₆ electrolyte, after cycling has a specific capacity of at least 38 mAh/g in all 1C, 2C, 4C, 2C and 1C cycling modes. In comparison, a battery with a CELGARD 2500 type separator (with the same electrolyte and general design) had a much lower specific capacity measured in the same cycling modes. Similarly, in FIG. 21 shows the results of various measurements of specific capacity for a battery according to the present invention and a CELGARD type battery selected for comparison. After more than 50 continuous cycles since the initial charge, the SEI-preformed batteries had dramatically different results. The battery of the present invention having the above electrolyte had a specific capacity of more than 100 mAh/g after such continuous 50 cycles. It should be noted that the comparative battery showed a significantly lower specific capacity, indicating an improved reliability of the battery according to the present invention, apparently due to the effective pre-formation of the SEI layer on the anode as well as the battery separator.

In order to demonstrate the overall results of the pre-formed SEI layer in the batteries in question (the battery of the present invention and the battery shown for comparison), some exemplary cells were essentially disassembled to determine the common SEI coating layer they contained both inside the separators and on separators. Thus, after completion of the cycling, exemplary pellet cells were dismounted in an argon-filled glove box and dried under vacuum prior to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) examination. Samples prepared for SEM and EDX studies were coated with gold/palladium. For the study by the SEM method, a scanning electron microscope of the Carl Zeiss Auriga-BU FIB FESEM brand was used. A scanning electron microscope with an energy dispersive spectrometer (a Bruker Nano microscope with an XFIash Detector 5030 attachment) was used for the EDX study. The study of separators by the EDX method resulted in spectra with peaks of atomic resonances shown in Table. 12.

______________________________ Table 12

Element CELGARD 2500 DWI Silver 25 Carbon 88.05 68.48 Oxygen 6.81 16.30 Fluorine 3.99 12.23 Phosphorus 1.15 3.00

These measurements show that the SEI layer is much better developed on the separator according to the present invention than on the comparative film separator. Thus, the measured value of the resonant peak of the carbon atom, which is a maximum of 70 in this case, the value of re

- 15 039132 oxygen atom resonance peak value of at least 8, fluorine atom resonance peak value of at least 5, and phosphorus atom resonance peak value of at least 1.5 in this situation are important to ensure a complete SEI -layer inside the battery. Such an SEI layer corresponds, as mentioned above, to increased reliability of initial charging and cycling, in particular within the layer co-existing on the anode and separator. Thus, batteries containing such an efficient resulting SEI layer, and a separator that facilitates its application of such a coating during cycling and at least initial charging, have, as noted above, an excellent initial capacity, also providing increased reliability during use and potentially longer storage time while waiting for such an initial charge inside the respective device (eg cell phone, etc.).

The exemplary method includes the following steps: assembling an element having an internal volume containing an anode, a cathode and a separator; filling the internal volume of the cell with electrolyte; connecting the anode and cathode to the charger; charging the cell at a charging rate that is less than or equal to C/6 until the cell reaches its maximum voltage; and charging the cell at a voltage that is higher than the predetermined voltage for more than 6 hours. The present invention also includes a method in which the voltage to complete the low-rate charging step is greater than or equal to 3.4 V. The present invention also includes a method according to which the voltage for the charging stage using high voltage is greater than 3.4V.

Embodiments of the present invention may include specific parameters that provide sufficient solid electrolyte interfacial layer such that the ideal applied current is no more than C/4, preferably no more than C/6, and more preferably no more than C/10 (where C is charge rate required to charge the cell to full capacity within one hour). In addition, the use of voltage is very important in that specific parameters ensure that a sufficient solid electrolyte interfacial layer is created so that the ideal voltage is achieved at a value greater than 3.3 V, preferably 3.6 V, and more preferably 3.9 V. In addition In addition, the current required to maintain the voltage above 3.6 V must be supplied for a sufficiently long period of time, which is more than 6 hours, preferably more than 9 hours and more preferably more than 12 hours. This process allows the formation of the SEI layer with a charge rate that is limited by the current (not the size of the separator pores), and also allows for a slow process at high voltage, whereby the SEI layer continues to fill all the gaps and provides uniform full coverage of the anode. As stated above, this anode coating is important to the overall reliability of the battery (and the length of the storage period, presumably prior to initial charging).

While the present invention has been shown and described in detail with reference to the preferred embodiments thereof and the accompanying drawings, those skilled in the art will appreciate that various changes in form and detail may be made therein without departing from the principle of the present invention. Thus, the scope of protection of the present invention is not defined by the detailed description, but by the appended claims.

Claims (10)

1. A method for manufacturing a lithium-ion battery, including: assembling an element, the internal volume of which contains an anode, a cathode and a separator, which contains entangled microfibers and nanofibers; filling the internal volume of the cell with electrolyte; connecting the anode and cathode to the charger; charging the cell at an applied current value not exceeding C/4 until the charge is complete, where C is the charging rate required to charge the cell to full capacity in one hour and at a voltage greater than 3.3 V for more than six hours . 2. A lithium-ion battery manufactured using the method of claim 1, comprising a cathode, an anode, a separator, and a liquid electrolyte, the separator comprising entangled microfibers and nanofibers, and a solid electrolyte interfacial layer. 3. The lithium ion battery of claim 2, wherein the separator contains randomly oriented fibers. 4. The lithium ion battery of claim 3, wherein at least one of the randomly oriented fibers has a largest transverse dimension of less than 1.0 µm. 5. A lithium ion battery according to any one of claims 2 to 4, wherein the separator has an effective average pore size that is greater than or equal to 0.1 µm. 6. A lithium-ion battery according to any one of claims 2-5, in which the solid electrolyte interfacial layer contains areas detectable by a scanning electron microscope, in which essentially all the pores present in the micrographs of the original separator obtained using the - 16 039132 scanning electron microscope, filled. 7. The lithium ion battery of claim 2, wherein the solid electrolyte interface contains areas in which the nanofibers present in the SEM micrographs of the original separator are not observed as being present because they are embedded in the solid electrolyte interface. 8. Lithium ion battery according to any one of claims 2 to 7, wherein the solid electrolyte interfacial layer contains regions which, if observed using energy dispersive X-ray spectroscopy, show phosphorus levels greater than 1.5%. 9. A lithium ion battery according to any one of claims 2 to 8, wherein the solid electrolyte interfacial layer contains regions which, if observed using energy dispersive X-ray spectroscopy, show fluorine levels greater than 5%. 10. The lithium ion battery of claim 2 having a specific capacity greater than 100 mAh/g for 50 continuous cycles following said initial charge.