BATTERY CELL COMPRISING AN ANODE ELECTRODE HAVING A Si-BASED ANODE ACTIVE MATERIAL WITH A

Abstract

The present invention provides a battery cell comprising C cathode electrodes, S separators, and A anode electrodes, each anode electrode comprising an anode active material layer disposed on an anode current collector. The anode active material layer includes N sub-layers, and at least two of the N sub-layers have different proportions of Si-based anode active material and graphite, where A, S, C, and N are integers greater than 1.

Description

Technical Field

[0001] The present disclosure relates to battery pack cells, and more particularly to battery pack cells including an anode electrode having a silicon-based anode active material with a stepped gradient concentration. Background Art

[0002] The information provided in this section is intended to generally introduce the background of the present disclosure. To the extent that the work currently attributed to the inventors is described in this section, and aspects of the specification that may not otherwise be determined to be prior art at the time of filing, are not expressly or impliedly admitted to be prior art against the present disclosure.

[0003] The present disclosure relates to battery pack cells, and more particularly to battery pack cells including an anode electrode having a silicon-based anode active material with a stepped gradient concentration.

[0004] Electric vehicles (EVs), such as battery electric vehicles (BEVs), hybrid vehicles, and / or fuel cell vehicles, include one or more electric motors and a battery pack system including one or more battery pack cells, modules, and / or battery packs. A power control system is used to control the charging and / or discharging of the battery pack system during charging and / or driving.

[0005] A battery pack cell includes a cathode electrode, an anode electrode, and a separator. The cathode electrode includes a cathode active material layer disposed on a cathode current collector. The anode electrode includes an anode active material layer disposed on an anode current collector. Summary of the Invention

[0006] A battery pack cell includes C cathode electrodes, S separators, and A anode electrodes, each anode electrode including an anode active material layer disposed on an anode current collector. The anode active material layer includes N sublayers, and at least two of the N sublayers have different ratios of silicon-based anode active material to graphite, where A, S, C, and N are integers greater than 1.

[0007] In other features, the silicon-based anode active material is selected from LSO, chemically lithiated SiOx, Si-C, Si, Si nanowires, and Si alloys. The N concentrations of the silicon-based anode active material in the N sublayers each increase monotonically with the lateral distance from the plane including the anode current collector. The N concentrations of the silicon-based anode active material in the N sublayers each decrease monotonically with the lateral distance from the plane including the anode current collector.

[0008] In other features, at least one of the N sublayers has a capacity loading of 1 mAh / cm 2 to 4 mAh / cm 2Layers lacking Si-based anode active material. At least one of the N sub-layers is a layer lacking Si-based anode active material having 0 wt% to 50 wt% of Si-based anode active material and 50 wt% to 100 wt% of graphite. At least one of the N sub-layers is a sub-layer lacking Si-based anode active material having 5 wt% to 20 wt% of Si-based anode active material and 80 wt% to 95 wt% of graphite. At least one of the N sub-layers is a sub-layer rich in Si-based anode active material containing 20 wt% to 70 wt% of Si-based anode active material and 30 wt% to 80 wt% of graphite. At least one of the N sub-layers is a sub-layer rich in Si-based anode active material containing 20 wt% to 50 wt% of Si-based anode active material and 50 wt% to 80 wt% of graphite.

[0009] Among other features, the anode active material layer further comprises a conductive additive and a binder. The conductive additive is selected from single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), SuperP, graphite, and graphite nanosheets. The binder is selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), CMS, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), PAA-PHEA, and combinations thereof.

[0010] A method for manufacturing an anode electrode for a battery pack cell, comprising depositing a first slurry mixture onto an anode current collector using a first die to form a first layer. The first slurry mixture comprises a first ratio of Si-based anode active material to graphite, a binder, a conductive additive, and a solvent. The method comprises depositing a second slurry mixture onto the anode current collector using one of the first die and a second die to form a second layer. The second slurry mixture comprises a second ratio of Si-based anode active material to graphite, a binder, a conductive additive, and a solvent, and wherein the first ratio and the second ratio are different. The method comprises drying the first layer and the second layer using an oven.

[0011] Among other features, the Si-based anode active material is selected from LSO, chemically lithiated SiOx, Si-C, Si, Si nanowires, and Si alloys. The first layer has a lower concentration of Si-based anode active material than the second layer.

[0012] Among other features, at least one of the first layer and the second layer is a sub-layer lacking Si-based anode active material having 5 wt% to 20 wt% of Si-based anode active material and 80 wt% to 95 wt% of graphite. At least one of the first layer and the second layer is a sub-layer rich in Si-based anode active material containing 20 wt% to 50 wt% of Si-based anode active material and 50 wt% to 80 wt% of graphite.

[0013] A method for manufacturing an anode electrode for a battery pack cell, comprising generating a first mixture comprising a first proportion of Si-based anode active material, graphite, a binder, and a conductive additive; mixing the first mixture to fibrillate the binder; forming a first free-standing layer using the first mixture; generating a second mixture comprising a second proportion of Si-based anode active material, graphite, a binder, and a conductive additive, wherein the first proportion and the second proportion are different; mixing the second mixture to fibrillate the binder; forming a second free-standing layer using the second mixture; thermally bonding the first free-standing layer to the second free-standing layer; and laminating the first free-standing layer and the second free-standing layer onto an anode current collector.

[0014] Among other features, the Si-based anode active material is selected from LSO, chemically lithiated SiOx, Si-C, Si, Si nanowires, and Si alloys. The first free-standing layer has a lower concentration of Si-based anode active material than the second free-standing layer. At least one of the first free-standing layer and the second free-standing layer is a sublayer lacking Si-based anode active material, which has 5 wt% to 20 wt% of Si-based anode active material and 80 wt% to 95 wt% of graphite. At least one of the first free-standing layer and the second free-standing layer is a sublayer rich in Si-based anode active material, which comprises 20 wt% to 50 wt% of Si-based anode active material and 50 wt% to 80 wt% of graphite.

[0015] The present invention discloses the following solutions:

[0016] Solution 1. A battery pack cell, comprising:

[0017] C cathode electrodes;

[0018] S separators; and

[0019] A anode electrodes, each anode electrode comprising an anode active material layer disposed on an anode current collector,

[0020] wherein the anode active material layer comprises N sublayers, and at least two of the N sublayers have different proportions of Si-based anode active material and graphite, wherein A, S, C, and N are integers greater than 1.

[0021] Solution 2. The battery pack cell according to Solution 1, wherein the Si-based anode active material is selected from LSO, chemically lithiated SiO x , Si-C, Si, Si nanowires, and Si alloys.

[0022] Solution 3. The battery pack cell according to Solution 1, wherein the N concentrations of the Si-based anode active material in the N sublayers respectively increase monotonically with the lateral distance from the plane including the anode current collector.

[0023] Embodiment 4. The battery pack battery according to Embodiment 1, wherein the N concentrations of the Si-based anode active material in the N sub-layers decrease monotonically with the lateral distance from the plane including the anode current collector.

[0024] Embodiment 5. The battery pack battery according to Embodiment 1, wherein at least one of the N sub-layers is a layer lacking Si-based anode active material with a capacity load of 1 mAh / cm 2 to 4 mAh / cm 2 of the layer.

[0025] Embodiment 6. The battery pack battery according to Embodiment 1, wherein at least one of the N sub-layers is a layer lacking Si-based anode active material, which has 0 wt% to 50 wt% of the Si-based anode active material and 50 wt% to 100 wt% of graphite.

[0026] Embodiment 7. The battery pack battery according to Embodiment 1, wherein at least one of the N sub-layers is a sub-layer lacking Si-based anode active material, which has 5 wt% to 20 wt% of the Si-based anode active material and 80 wt% to 95 wt% of graphite.

[0027] Embodiment 8. The battery pack battery according to Embodiment 1, wherein at least one of the N sub-layers is a sub-layer rich in Si-based anode active material, which contains 20 wt% to 70 wt% of the Si-based anode active material and 30 wt% to 80 wt% of graphite.

[0028] Embodiment 9. The battery pack battery according to Embodiment 2, wherein at least one of the N sub-layers is a sub-layer rich in Si-based anode active material, which contains 20 wt% to 50 wt% of the Si-based anode active material and 50 wt% to 80 wt% of graphite.

[0029] Embodiment 10. The battery pack battery according to Embodiment 1, wherein:

[0030] the anode active material layer further comprises a conductive additive and a binder,

[0031] the conductive additive is selected from single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), Super P, graphite and graphite nanosheets; and

[0032] the binder is selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), CMS, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), PAA-PHEA and combinations thereof.

[0033] Scheme 11. A method for manufacturing an anode electrode of a battery pack cell, comprising:

[0034] Depositing a first slurry mixture onto an anode current collector using a first die to form a first layer,

[0035] wherein the first slurry mixture comprises a first proportion of Si-based anode active material and graphite, a binder, a conductive additive, and a solvent;

[0036] Depositing a second slurry mixture onto the anode current collector using one of the first die and a second die to form a second layer,

[0037] wherein the second slurry mixture comprises a second proportion of Si-based anode active material and graphite, a binder, a conductive additive, and a solvent, and wherein the first proportion and the second proportion are different; and

[0038] Drying the first layer and the second layer using an oven.

[0039] Scheme 12. The method according to Scheme 11, wherein the Si-based anode active material is selected from LSO, chemically lithiated SiO x , Si-C, Si, Si nanowires, and Si alloys.

[0040] Scheme 13. The method according to Scheme 11, wherein the first layer has a lower concentration of Si-based anode active material than the second layer.

[0041] Scheme 14. The method according to Scheme 11, wherein at least one of the first layer and the second layer is a sub-layer lacking Si-based anode active material, which has 5 wt% to 20 wt% of Si-based anode active material and 80 wt% to 95 wt% of graphite.

[0042] Scheme 15. The method according to Scheme 11, wherein at least one of the first layer and the second layer is a sub-layer rich in Si-based anode active material, which comprises 20 wt% to 50 wt% of the Si-based anode active material and 50 wt% to 80 wt% of graphite.

[0043] Scheme 16. A method for manufacturing an anode electrode of a battery pack cell, comprising:

[0044] Generating a first mixture comprising a first proportion of Si-based anode active material and graphite, a binder, and a conductive additive;

[0045] Mixing the first mixture to fibrillate the binder;

[0046] Using the first mixture to form a first self-supporting layer;

[0047] Produce a second mixture comprising a second proportion of Si-based anode active material, graphite, a binder, and a conductive additive, wherein the first proportion and the second proportion are different;

[0048] Mix the second mixture to fibrillate the binder;

[0049] Use the second mixture to form a second self-standing layer;

[0050] Thermally bond the first self-standing layer to the second self-standing layer; and

[0051] Laminate the first self-standing layer and the second self-standing layer onto an anode current collector.

[0052] Aspect 17. The method according to Aspect 16, wherein the Si-based anode active material is selected from LSO, chemically lithiated SiO x , Si-C, Si, Si nanowires, and Si alloys.

[0053] Aspect 18. The method according to Aspect 16, wherein the first self-standing layer has a lower concentration of Si-based anode active material than the second self-standing layer.

[0054] Aspect 19. The method according to Aspect 16, wherein at least one of the first self-standing layer and the second self-standing layer is a sub-layer lacking Si-based anode active material, which has 5 wt% to 20 wt% of Si-based anode active material and 80 wt% to 95 wt% of graphite.

[0055] Aspect 20. The method according to Aspect 16, wherein at least one of the first self-standing layer and the second self-standing layer is a sub-layer rich in Si-based anode active material, which comprises 20 wt% to 50 wt% of the Si-based anode active material and 50 wt% to 80 wt% of graphite.

[0056] From the detailed description, the claims, and the drawings, further applicable fields of the present disclosure will become apparent. The detailed description and specific examples are only intended to illustrate and are not intended to limit the scope of the present disclosure. Brief Description of the Drawings

[0057] The present disclosure will be more fully understood through the detailed description and the drawings, wherein:

[0058] Figure 1 is a side cross-sectional view of an example of a battery cell of a battery pack, the battery cell of the battery pack comprising A anode electrodes each containing a stepped gradient concentration of Si-based anode active material, C cathode electrodes, and S separators;

[0059] Figure 2An example of a side cross-sectional view of one of the A anode electrodes including a Si-based anode active material with an increasing stepped gradient concentration according to the present disclosure;

[0060] Figure 3 An example of a side cross-sectional view of one of the A anode electrodes including a Si-based anode active material with a decreasing stepped gradient concentration according to the present disclosure;

[0061] Figure 4 An example illustrating a method of manufacturing the A anode electrodes including a Si-based anode active material with a stepped gradient concentration according to the present disclosure;

[0062] Figure 5 An example illustrating a method of manufacturing the A anode electrodes including a Si-based anode active material with a stepped gradient concentration according to the present disclosure;

[0063] Figure 6 A scanning electron microscope (SEM) image of an example of an active material layer of an anode electrode according to the present disclosure;

[0064] Figure 7 A graph showing the variation of voltage with load during the first cycle of an anode electrode including a uniform anode active material layer and an anode electrode including a stepped gradient anode active material layer according to the present disclosure at a charge rate of C / 20 and a temperature of 25°C; and

[0065] Figure 8 A graph showing the variation of voltage with load during the first cycle of an anode electrode including a uniform anode active material layer and an anode electrode including a stepped gradient anode active material layer according to the present disclosure at a charge rate of C / 5 and a temperature of 25°C.

[0066] In the drawings, reference numerals may be reused to identify similar and / or identical elements. Detailed Description

[0067] Although the battery pack cells according to the present disclosure are shown in the context of an electric vehicle, the battery pack cells can be used in stationary applications and / or other applications.

[0068] Silicon-based anode active materials such as lithiated silicon oxide (LSO) have a high first Coulombic efficiency (>90%) and a large reverse specific capacity (-1400 mAh / g). Some anode electrodes may include an anode active material layer that contains a homogeneous mixture of a Si-based anode active material and graphite rather than pure graphite. However, silicon materials significantly expand and contract during cycling.

[0069] The present disclosure relates to a battery cell of a battery pack that includes an anode electrode, the anode electrode including an anode active material layer having a plurality of sub-layers, the plurality of sub-layers including Si-based anode active material having a stepped gradient concentration to improve fast charging and / or cycling performance of the battery cell of the battery pack. In other words, the anode active material layer includes N sub-layers, each sub-layer including a different concentration (e.g., an increasing or decreasing concentration) of Si-based anode active material, where N is an integer greater than 1. In some instances, the concentration of the Si-based anode active material is uniform within a given sub-layer and increases or decreases monotonically from one sub-layer to another.

[0070] In some instances, the stepped gradient concentration includes an increasing concentration of Si-based anode active material (e.g., LSO) in a lateral direction away from a plane including the anode current collector. For example, the anode active material layer includes an outer layer rich in LSO and an inner layer lacking LSO disposed adjacent to the anode current collector. Compared to an anode electrode having a uniform LSO concentration, the outermost layer rich in LSO rapidly conducts to deposit lithium ions (Li + ) and release volume expansion outwardly. The inner layer lacking LSO (richer in graphite than the outer layer rich in LSO) provides a highly conductive path for electrons to facilitate fast charging (e.g., at a charge rate > 3C). The lower concentration of LSO in the inner layer lacking LSO reduces the expansion of the inner layer, thereby reducing the risk of delamination of the anode active material layer due to volume expansion during direct current fast charging (DCFC).

[0071] Now referring Figure 1 , the battery cell 10 of the battery pack includes C cathode electrodes 20, A anode electrodes 40, and S separators 32 arranged in a battery cell stack 12 in a predetermined order, where C, S, and A are integers greater than zero. The battery cell stack 12 is disposed in a housing 50. The C cathode electrodes 20-1, 20-2,... and 20-C include cathode active material layers 24 disposed on one or both sides of a cathode current collector 26.

[0072] The A anode electrodes 40-1, 40-2,... and 40-A include anode active material layers 42 disposed on one or both sides of an anode current collector 46. The anode active material layer 42 includes sub-layers of Si-based anode active material (e.g., LSO) having a stepped gradient concentration in a direction transverse to the plane including the anode current collector. In some instances, the cathode active material layer 24 and / or the anode active material layer 42 include coatings applied or cast onto the current collector using a wet or dry method, the coatings including one or more active materials, one or more conductive additives, and / or one or more binder materials. The A anode electrodes 40 and the C cathode electrodes 20 exchange lithium ions during charge / discharge.

[0073] In some instances, the cathode current collector 26 and / or the anode current collector 46 includes a metal foil, a metal mesh, a perforated metal, a three-dimensional (3D) metal foam, and / or a porous metal. In some instances, the current collector is made of one or more materials selected from copper, stainless steel, brass, bronze, zinc, aluminum, and / or their alloys. The external tabs 28 and 48 are connected to the current collectors of the cathode electrode and the anode electrode, respectively, and may be disposed on the same side or different sides of the battery cell stack 12 of the battery pack. The external tabs 28 and 48 are connected to the terminals of the battery cells of the battery pack.

[0074] Now referring Figure 2 and Figure 3 , an example of one of the A anode electrodes 40 is shown. In Figure 2 , the anode active material layer 42 includes N sub-layers, each sub-layer including a different concentration of Si-based anode active material 62, where N is an integer greater than 1. For example, as the lateral distance between a corresponding one of the N sub-layers and the plane including the anode current collector 46 increases, the concentration of the Si-based anode active material 62 increases and the concentration of the graphite 60 decreases. In other words, the sub-layer L1 adjacent to the anode current collector 46 has a lower concentration of the Si-based anode active material 62 than the sub-layer L2. The sub-layer L1 has a higher concentration of graphite than the sub-layer L2. Although N = 2 in Figure 2 , N can be greater than 2.

[0075] In some instances, the sub-layer L2 contains 40 wt% of the Si-based anode active material and 60 wt% of the graphite. The sub-layer L2 provides sufficient Li + diffusion channels, and the Si-based anode active material with a high working potential conducts rapidly to effectively deposit Li + , without Li plating. The gradient concentration of the sub-layer L2 improves the fast charging ability.

[0076] The sub-layer L1 contains 20 wt% of the Si-based anode active material and 80 wt% of the graphite. The high electron conductivity provides sufficient electrons during fast charging and maintains a fast state of charge (SOC) balance between the layers (e.g., between the sub-layers L1 and L2). The sub-layer L1 has a reduced volume expansion to maintain a strong adhesion between the anode active material layer and the anode current collector, thereby maintaining the battery cycling performance.

[0077] In Figure 3In [the anode active material layer 42], the anode active material layer 42 includes N sub-layers, which include Si-based anode active materials 62 and graphite 60 at different concentrations. In other words, as the lateral distance between a corresponding one of the N sub-layers and the plane including the anode current collector 46 increases, the concentration of the Si-based anode active material decreases and the concentration of graphite increases. In other words, sub-layer L1 has a higher concentration of Si-based anode active material than sub-layer L2, and sub-layer L1 has a lower concentration of graphite than sub-layer L2. In Figure 3 [this case], N = 2, but N can be greater than 2.

[0078] In some examples, the anode active material layer 42 includes a Si-based active material, graphite, a binder, and a conductive additive. In some examples, the Si-based anode active material and graphite account for 84 wt% to 99 wt% of the anode active material layer 42, the binder accounts for 0.5 wt% to 8 wt% of the anode active material layer 42, and the conductive additive accounts for 0.5 wt% to 8 wt% of the anode active material layer 42.

[0079] In some examples, the anode active material layer 42 includes N sub-layers (e.g., on each side of the anode current collector 46), where N is an integer greater than 1. One or more of the N layers have different ratios of Si-based anode active material and graphite. In some examples, the concentration of the Si-based anode active material in each of the N sub-layers is 20 wt% to 70 wt%. In some examples, the capacity loading is 3 mAh / cm 2 to 8 mAh / cm 2 (for a single-sided coating at 0.1C at room temperature). In some examples, the capacity loading is 4 to 6 mAh / cm 2 (for a single-sided coating at 0.1C at room temperature). In some examples, the press density is 1.6 + / - 0.5 g / cm 3 .

[0080] In some examples, the N sub-layers include a layer rich in Si-based anode active material and a layer lacking Si-based anode active material. In some examples, the layer rich in Si-based anode active material contains 20 wt% to 70 wt% of Si-based anode active material and 30 wt% to 80 wt% of graphite. In other examples, the layer rich in Si-based anode active material contains 20 wt% to 50 wt% of Si-based anode active material and 50 wt% to 80 wt% of graphite.

[0081] In some examples, the capacity loading of the layer rich in Si-based anode active material is 1 mAh / cm 2 to 4 mAh / cm 2(For a single-sided coating at 0.1C at room temperature). In some instances, the capacity loading of the layer rich in Si-based anode active material is 2 mAh / cm 2 to 4 mAh / cm 2 (For a single-sided coating at 0.1C at room temperature). In some instances, the porosity is 25% to 50%.

[0082] In some instances, the layer lacking Si-based anode active material contains 0 wt% to 50 wt% of Si-based anode active material and 50 wt% to 100 wt% of graphite. In some instances, the layer rich in Si-based anode active material contains 5 wt% to 20 wt% of Si-based anode active material and 80 wt% to 95 wt% of graphite. In some instances, the capacity loading of the layer lacking Si-based anode active material is 1 mAh / cm 2 to 4 mAh / cm 2 (For a single-sided coating at 0.1C at room temperature). In some instances, the capacity loading of the layer rich in Si-based anode active material is 1 mAh / cm 2 to 3 mAh / cm 2 (For a single-sided coating at 0.1C at room temperature). In some instances, the porosity is 25% to 50%.

[0083] In some instances, the Si-based anode active material is selected from LSO, chemically lithiated silicon oxide SiO x , Si-C, Si, Si nanowires, and Si alloys. In some instances, the Si-based anode active material includes Li y SiO x (0 < x < 2 and 0 < y < 1). In some instances, the D50 particle size is 3 μm to 20 μm. In some instances, the Brunauer, Emmet, and Teller surface area is 0.5 m 2 / g to 10 m 2 / g. In some instances, the tapped density (TD) is 0.8 g / cc to 1.5 g / cc. The morphology of the silicon-based material can be nanoparticles, nanofibers, nanotubes, and micron particles.

[0084] In some instances, the graphite includes particles with a D50 size of 6 μm to 20 μm. In some instances, the BET surface area is 1 m 2 / g to 10 m 2 / g. In some instances, the TD is 0.8 g / cc to 1.5 g / cc.

[0085] In some examples, the conductive additive includes single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), SuperP, graphite, and graphite nanosheets. In some examples, the binder is selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), CMS, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), PAA-PHEA, and combinations thereof. In some examples, PAA is neutralized with sodium hydroxide (NaOH) or lithium hydroxide (LiOH) (e.g., sodium polyacrylate (PAANa), PAAH 0.2 Na 0.8 or lithium polyacrylate (LiPAA)).

[0086] In some examples, a slurry coating method is used to fabricate the anode electrode. In other examples, fabricating the anode electrode using a dry process includes fibrillating PTFE as the binder.

[0087] Now referring to Figure 4 , an example of the slurry coating method is shown. A first slurry mixture for the first layer 124 or L1 of the anode active material layer (e.g., LSO with graphite, conductive additive, and binder in a first ratio) is mixed with a solvent and supplied to a slotted die 120. The anode current collector 114 is supplied by a roll 110 to surround a roll 118 disposed adjacent to the slotted die 120. The slotted die 120 coats the first slurry onto the anode current collector 114 to form the first layer 124.

[0088] A second slurry mixture for the second layer 134 or L2 of the anode active material layer (e.g., LSO with graphite, conductive additive, and binder under a second blend) is mixed with a solvent and supplied to a slotted die 132. The anode current collector 114 having the first layer 124 is supplied to surround a roll 126 disposed adjacent to the slotted die 132. The slotted die 132 coats the second slurry onto the anode current collector 114 to form the second layer 134.

[0089] The anode current collector 114 having the first layer 124 and the second layer 134 passes through an oven 140 to remove the solvent and dry the first layer 124 and the second layer 134. The anode electrode 142 passes through guide rolls 144 and 148 and is collected on a roll 152.

[0090] In other examples, the first layer 124 can optionally be dried by another oven between the rolls 118 and 128. In other examples, a slotted die having two slots can be used to sequentially apply both the first layer 124 and the second layer 134.

[0091] Now referring to Figure 5, an example of a dry manufacturing method is shown. At 210, a Si-based anode active material and graphite in a first ratio are mixed with a polytetrafluoroethylene (PTFE) binder and a conductive additive and fibrillated. At 212, the first fibrillated mixture is pressed, calendered, and / or shaped to form a first self-supporting film. At 214, a Si-based anode active material and graphite in a second ratio are mixed with a polytetrafluoroethylene (PTFE) binder and a conductive additive and fibrillated. At 216, the second fibrillated mixture is pressed, calendered, and / or shaped to form a second self-supporting film. At 218, the first self-supporting film and the second self-supporting film are attached together using a thermal joint (e.g., an adhesive). At 222, the first film and the second film are laminated onto an anode current collector.

[0092] Now referring to Figures 6 to 8 , an example of a battery cell of a battery pack including an anode electrode having an inner layer lacking LSO and an outer layer rich in LSO is shown. The layer lacking LSO contains 20 wt% LSO and 80 wt% graphite. The layer rich in LSO contains 40 wt% LSO and 60 wt% graphite. The binder includes PTFE. In Figure 6 , the SEM image shows graphite, LSO, and fibrillated PTFE.

[0093] In Figure 7 , the stepped-gradient anode electrode 314 is compared with a single-layer anode electrode 310 having 30 wt% LSO and 70 wt% graphite. Lithiation is performed at C / 20 continuous current and 10 mV continuous voltage (CCCV) with a taper of C / 100. Delithiation is performed at 2V, C / 20. The electrolyte includes 1M LiPF6 in EC / EMC. Both electrodes provide the same capacity and first Coulombic efficiency (CE) (e.g., ~87%). In Figure 8 , the anode electrode having a stepped-gradient LSO concentration exhibits a higher lithiation capacity than the single-layer anode electrode 310.

[0094] The foregoing description is exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while the disclosure includes specific examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be implemented in a different order (or concurrently) without altering the principles of the disclosure. Further, although the embodiments are described above as having certain features, any one or more of the features described with respect to any one embodiment of the disclosure can be implemented in any other embodiment and / or combined with the features of any other embodiment, even if not explicitly described as such. In other words, the described embodiments are not mutually exclusive, and a permutation of one or more of the embodiments is still within the scope of the disclosure.

[0095] Various terms are used to describe spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.), including “connected,” “engaged,” “coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and “disposed.” Unless explicitly described as “direct,” when the relationship between a first element and a second element is described in the foregoing disclosure, the relationship can be a direct relationship in which no other intervening elements exist between the first and second elements, or an indirect relationship in which one or more intervening elements exist (spatially or functionally) between the first and second elements. The phrase “at least one of A, B, and C” as used herein should be construed to mean a logical (A or B or C) using a non-exclusive logical OR and should not be construed to mean “at least one of A, at least one of B, and at least one of C.”

[0096] In the drawings, the direction of an arrow as shown by the arrowhead generally demonstrates the flow of information (such as data or instructions) associated with the illustration. For example, when elements A and B exchange various information but the information transmitted from element A to element B is associated with the illustration, the arrow can point from element A to element B. Such a unidirectional arrow does not mean that no other information is transmitted from element B to element A. Further, for the information transmitted from element A to element B, element B can send a request for that information or receive an acknowledgment back from element A.

Claims

1. A battery cell for a battery pack, comprising: C cathode electrodes; S separators; and A anode electrodes, each anode electrode including an anode active material layer disposed on an anode current collector, wherein the anode active material layer includes N sub-layers, and at least two of the N sub-layers have different ratios of Si-based anode active material to graphite, where A, S, C, and N are integers greater than 1.

2. The battery of the battery pack according to claim 1, wherein the Si-based anode active material is selected from LSO, chemically lithiated SiO x , Si-C, Si, Si nanowires, and Si alloys.

3. The battery cell for a battery pack according to claim 1, wherein the N concentrations of the Si-based anode active material in the N sub-layers each increase monotonically with the lateral distance from the plane including the anode current collector.

4. The battery cell for a battery pack according to claim 1, wherein the N concentrations of the Si-based anode active material in the N sub-layers each decrease monotonically with the lateral distance from the plane including the anode current collector.

5. The battery of the battery pack according to claim 1, wherein at least one of the N sub-layers is a layer lacking a Si-based anode active material with a capacity load of 1 mAh / cm 2 to 4 mAh / cm 2 of the layer.

6. The battery cell for a battery pack according to claim 1, wherein at least one of the N sub-layers is a layer lacking Si-based anode active material, having 0 wt% to 50 wt% of the Si-based anode active material and 50 wt% to 100 wt% of graphite.

7. The battery cell for a battery pack according to claim 1, wherein at least one of the N sub-layers is a sub-layer lacking Si-based anode active material, having 5 wt% to 20 wt% of the Si-based anode active material and 80 wt% to 95 wt% of graphite.

8. The battery cell for a battery pack according to claim 1, wherein at least one of the N sub-layers is a sub-layer rich in Si-based anode active material, comprising 20 wt% to 70 wt% of the Si-based anode active material and 30 wt% to 80 wt% of graphite.

9. The battery cell for a battery pack according to claim 2, wherein at least one of the N sub-layers is a sub-layer rich in Si-based anode active material, comprising 20 wt% to 50 wt% of the Si-based anode active material and 50 wt% to 80 wt% of graphite.

10. The battery cell for a battery pack according to claim 1, wherein: the anode active material layer further comprises a conductive additive and a binder, the conductive additive is selected from single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), Super P, graphite, and graphite nanosheets; and the binder is selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), CMS, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), PAA-PHEA, and combinations thereof.

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