ELECTRODE STRUCTURE OF LITHIUM ION BATTERY

Abstract

An electrode structure of a lithium ion battery includes a current collector, at least one energy active layer, and at least one power active layer. The energy active layer is formed on the current collector and the power active layer is formed on the energy active layer. The energy active layer includes a first lithium-containing compound and multiple first conductive particles. The power active layer includes a second lithium-containing compound and multiple second conductive particles. The first lithium-containing compound includes lithium manganese cobalt nickel oxide (LiMnxCoyNizO2), where 0

Description

TECHNICAL FIELD

The disclosure relates in general to an electrode structure of a lithium ion battery, and more particularly to an electrode structure having an energy active layer and a power active layer for a lithium ion battery.

BACKGROUND

With surging oil prices and the emergence of carbon reduction awareness, electric vehicles are gradually becoming a rising focus in the market. Electric vehicles are available in hybrid vehicles (including plug-ins) and pure electric vehicles. A powering system of an electric vehicle is generally formed by three main components, namely a battery module type, power unit control and motor transmission. A vehicle battery is the primary core power source of an electric vehicle. In other words, the performance of an electric vehicle greatly depends on the performance of the battery powering the vehicle.

Lithium ion batteries are commonly utilized as vehicle batteries. Therefore, extensive researches are dedicated to increasing energy density, power density, safety and cycle life of lithium ion batteries in order to enhance the performance of vehicle batteries.

SUMMARY

According to an embodiment of the disclosure, an electrode structure of a lithium ion battery is provided. The electrode structure comprises a current collector, at least one energy active layer, and at least one power active layer. The energy active layer is formed on the current collector and the power active layer is formed on the energy active layer. The energy active layer comprises a first lithium-containing compound and a plurality of first conductive particles. The power active layer comprises a second lithium-containing compound and a plurality of second conductive particles. The first lithium-containing compound comprises lithium manganese cobalt nickel oxide (LiMn_xCo_yNi_zO₂), where 0<x, y, z<1. The second lithium-containing compound comprises lithium manganese oxide (LiMn₂O₄). A weight ratio of the first conductive particles to the energy active layer is greater than a weight ratio of the second conductive particles to the power active layer. A lithium ion diffusion coefficient of the second lithium-containing compound is greater than that of the first lithium-containing compound. A specific capacity of the first lithium-containing compound is greater than that of the second lithium-containing compound.

A detailed description is given in the following embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of an electrode structure of a lithium ion battery according to a first embodiment of the present disclosure.

FIG. 2 is a schematic diagram of an electrode structure of a lithium ion battery according to a second embodiment of the present disclosure.

FIG. 3 is a schematic diagram of an electrode structure of a lithium ion battery according to a third embodiment of the present disclosure.

FIG. 4 is a schematic diagram of an electrode structure of a lithium ion battery according to a fourth embodiment of the present disclosure.

In the drawings, same denotations represent the same or similar elements. It should be noted that the drawings are simplified for clear illustrations of the embodiments, and specific details disclosed in the embodiments are for examples for explaining the disclosure and are not to be construed as limitations. A person having ordinary skill in the art may modify or change corresponding structures according to actual applications.

DETAILED DESCRIPTION

In an embodiment of the disclosure, an electrode structure of a lithium ion battery comprises a current collector, at least one energy active layer, and at least one power active layer. The energy active layer is formed on the current collector and the power active layer is formed on the energy active layer. The energy active layer comprises a first lithium-containing compound and a plurality of first conductive particles. The power active layer comprises a second lithium-containing compound and a plurality of second conductive particles. The first lithium-containing compound comprises lithium manganese cobalt nickel oxide (LiMn_xCo_yNi_zO₂), where 0<x, y, z<1. The second lithium-containing compound comprises lithium manganese oxide (LiMn₂O₄). A weight ratio of the first conductive particles to the energy active layer is greater than a weight ratio of the second conductive particles to the power active layer. A lithium ion diffusion coefficient of the second lithium-containing compound is greater than that of the first lithium-containing compound. A specific capacity of the first lithium-containing compound is greater than that of the second lithium-containing compound.

FIG. 1 shows a schematic diagram of an electrode structure of a lithium ion battery according to a first embodiment of the present disclosure. Referring to FIG. 1, an electrode structure 100 of a lithium ion battery comprises a current collector 110, at least one energy active layer 120 and at least one power active layer 130. The energy active layer 120 is formed on the current collector 110, and the power active layer 130 is formed on the energy active layer 120, such that the energy active layer 120 is formed between the current collector 110 and the power active layer 130. The energy active layer 120 comprises a first lithium-containing compound and a plurality of first conductive particles. For example, the first lithium-containing compound is a lithium-containing complex transitional metal oxide. The composition of the lithium-containing complex transitional metal oxide (the first lithium-containing compound) includes at least one of nickel (Ni), cobalt (Co) or manganese (Mn). The power active layer 130 comprises a second lithium-containing compound and a plurality of second conductive particles. For example, the second lithium-containing compound is a lithium-containing complex transitional metal oxide. The composition of the lithium-containing complex transitional metal oxide (the second lithium-containing compound) includes at least one of Ni, Co or Mn. A lithium ion diffusion coefficient of the second lithium-containing compound is greater than that of the first lithium-containing compound. A specific capacity of the first lithium-containing compound is greater than that of the second lithium-containing compound. With the multi-layer structure formed from the at least one energy active layer 120 and the at least one power active layer 130, by incorporating the first lithium-containing compound with a high ion transmission efficiency of the second lithium-containing compound, the electrode structure 100 of a lithium ion battery is not only capable of performing high-efficiency discharge but offered with a prolonged cycle life.

In one embodiment, as shown in FIG. 1, for example, the first lithium-containing compound comprises lithium manganese cobalt nickel oxide (LiMn_xCo_yNi_zO₂), where 0<x, y, z<1, and the second lithium-containing compound comprises lithium manganese oxide (LiMn₂O₄).

According to an embodiment of the disclosure, the electrode structure 100 is a cathode of lithium ion battery. However, in applications, electrode structure 100 of a lithium ion battery may be cathode or anode, which is depending on the conditions applied and not limited thereto.

In the embodiment, the energy active layer 120 and the power active layer 130 may have the same thickness or different thicknesses. For example, the ratio of the thickness of the energy active layer 120 to the thickness of the power active layer 130 may be 5:5 to 7:3. In one embodiment, as shown in FIG. 1, for example, the thickness T1 of the energy active layer 120 is greater than the thickness T2 of the power active layer 130. Since the energy active layer 120 has a higher capacity than that of the power active layer 130, the optimization of the high-power and high-capacity characteristics of the electrode structure 100 can be achieved, and the overall capacity of the electrode structure 100 will not be reduced caused by a large thickness of the power active layer 130.

In the embodiment, the specific capacity of the first lithium-containing compound may be greater than or equal to 140 mAh/g.

In the embodiment, the first lithium-containing compound includes, for example, one or a combination of two or more of lithium cobalt oxide (LiCoO₂), lithium nickel oxide (LiNiO₂), lithium manganese oxide (LiMn₂O₄), a lithium-containing ternary oxide and a lithium phosphate compound. In the embodiment, the lithium-containing ternary oxide may be lithium manganese cobalt nickel oxide (LiMn_xCo_yNi_zO₂), where 0<x, y, z<1, or lithium nickel cobalt aluminum oxide (LiNi_xCo_yAl_zO₂), where 0<x, y, z<1, but not limited thereto. In the embodiment, a chemical formula of a lithium phosphate compound is LiMPO₄, where M is Fe, Ni or Mn. In an embodiment, the lithium phosphate compound may be LiFePO₄. However, the selections of the type of the first lithium-containing compound may vary depending on the conditions applied and are not limited thereto.

In the embodiment, the second lithium-containing compound has a lithium ion diffusion coefficient greater than or equal to 10⁻⁷ cm²/s. For example, the second lithium-containing compound may be LiMn₂O₄ (a spinel structure), or other types of lithium-containing compounds. The second lithium-containing compound may be one or a combination of two or more lithium-containing compounds having a lithium ion diffusion coefficient greater than or equal to 10⁻⁷ cm²/s. In one embodiment, the second lithium-containing compound may be a compound having a three-dimensional network structure, e.g., a compound having a cubic system lattice structure, such as LiMn₂O₄ (a spinel), having a ion transmission capability greater than that of a common layer structured active material (e.g., LiNi_1/3Mn_1/3Co_1/3O₂). In an alternative embodiment, the second lithium-containing compound may also be a layer-structured active material with a dopant, which increases the ion transmission capability of the layer-structured active material. In the embodiment, the lithium ion diffusion coefficient of LiMn₂O₄ is approximately 10⁻⁷ cm/s, the lithium ion diffusion coefficient of LiCoO₂ and LiNi_1/3Mn_1/3CO_1/3O₂ is approximately 10⁻⁸ cm/s, and the lithium ion diffusion coefficient of LiFePO₄ is approximately from 10⁻¹⁰ to 10⁻¹¹ cm/s. However, in addition to the above examples, given that the lithium ion diffusion coefficient of the second lithium-containing compound is greater than that of first lithium-containing compound, the selections of the types of the first and second lithium-containing compounds may vary according to the conditions applied and are not limited thereto.

In the embodiment, the first conductive particles are uniformly mixed in the energy active layer 120, and the second conductive particles are uniformly mixed in the power active layer 130 to achieve a preferred electron transmission effect. For example, the first conductive particles and the second conductive particles are respectively one or a combination of two or more of vapor grown carbon fiber (VGCF), conductive carbon black (such as Super P and KS6), graphite, a nano-sized carbon material, and acetylene black. In the embodiment, the first conductive particles and the second conductive particles may be selected from the same or different materials. However, in addition to the above examples, the selections of the types of the first conductive particles and the second conductive particles may vary according to the conditions applied and are not limited thereto.

In one embodiment, the weight ratio of the first conductive particles to the energy active layer 120 may be 0.5 to 20 wt %. In the embodiment, the weight ratio of the first conductive particles to the energy active layer 120 may be 0.5 to 5 wt %. In one embodiment, the first conductive particles may have a specific surface area of 10 m²/g to 100 m²/g.

In one embodiment, the weight ratio of the second conductive particles to the power active layer 130 may be 3 to 80 wt %. In the embodiment, the weight ratio of the second conductive particles to the power active layer 130 may be 5 to 50 wt %. In one embodiment, the second conductive particles may have a specific surface area of 10 m²/g to 100 m²/g.

In one embodiment, the weight ratio of the first conductive particles to the energy active layer 120 may be greater than the weight ratio of the second conductive particles to the power active layer 130. In the embodiment, the specific surface area of the first conductive particles in the energy active layer 120 is greater than the specific surface area of the first conductive particles in the power active layer 130.

In the embodiment, by incorporating the power active layer 130 having a high capacity with the first conductive particles having a high specific surface area and a high concentration in the energy active layer 120, the electron transmission capability (i.e., the electricity conductivity) can be increased. Compared to a conventional electrode structure having a single active material layer, the electrode structure according to the embodiments of the disclosure achieves a lower loss in the overall capacity under high-power discharge.

In one embodiment, the first lithium-containing compound and the second lithium-containing compound may both include lithium-containing manganese compounds. For example, the first lithium-containing compound may be LiNi_0.4Mn_0.4Co_0.2O₂, and the second lithium-containing compound may be LiMn₂O₄. When compositions of the lithium-containing compounds in both of the energy active layer 120 and the power active layer 130 include manganese, a high compatibility is provided in battery applications in contribution to the same element utilized. Further, as LiMn₂O₄ has a rather high platform voltage at about 3.9 V, that is close to an operating voltage (usually 3.7 V) of a common lithium ion battery, cross utilization and operations of products are further favored.

Further, in the embodiment, as shown in FIG. 1, the power active layer 130 is formed on the energy active layer 120, and both of the energy active layer 120 and the power active layer 130 contain lithium-containing manganese compounds. The insertion and extraction of the lithium ions cause an oxidation-reduction reaction, and so the lithium-containing manganese compound (e.g. LiMn₂O₄) in the power active layer 130 is allowed to in advance transform into a more stable tetravalent manganese (Me) layer. By the Mn⁴⁺ layer effectively protecting the lithium-containing manganese compound (e.g. lithium-containing nickel cobalt manganese compound) having a high capacity in the energy active material layer 130 underneath, an overall amount of dissolved manganese in the electrode structure can be reduced, and hence the cycle life is prolonged. Further, due to the better chemical stability and safety of coupling of trivalent and tetravalent manganese (Mn³⁺/⁴⁺) ions over those of coupling of trivalent and tetravalent cobalt (Co³⁺/⁴⁺), the amount of trivalent and tetravalent manganese (Mn³⁺/⁴⁺) in the two-layered structure according to the embodiments of the disclosure is greater than that in a conventional single-layered electrode structure, thereby promoting the corresponding stability in an electrochemical cycle.

In the embodiment, the energy active layer 120 and the power active layer 130 in the electrode structure 100 of a lithium ion battery may further comprise a binder, respectively. In the embodiment, the first lithium-containing compound and the first conductive particles form the energy active layer 120 via the binder, and the second lithium-containing compound and the second conductive particles form the power active layer 130 via the binder.

FIG. 2 shows a schematic diagram of an electrode structure of a lithium ion battery according to a second embodiment of the present disclosure. Elements sharing the same labeling are the same elements. Details of the same elements can be referred from associated descriptions of the foregoing embodiments, and shall be omitted herein.

Referring to FIG. 2, the difference of the present embodiment from the embodiments as shown in FIG. 1 is in that, an electrode structure 300 of a lithium ion battery comprises two power active layers 130 and 130′, which are formed on a first surface 110a of the current collector 110. The energy active layer 120 is formed between the two power active layers 130 and 130′. Characteristics of the power active layer 130′, material types included in the power active layer 130′, and material types for forming the power active layer 130′ are the same as those for the power active layer 130, and the related descriptions can be referred from foregoing descriptions associated with the power active layer 130. However, the selections of the types of the lithium-containing compounds in the power active layer 130 and in the power active layer 130′ may vary according to the conditions applied. Given that the lithium ion diffusion coefficients of the lithium-containing compounds in the two power active layers 130 and 130′ are greater than that of the first lithium-containing compound in the energy active layer 120, the lithium-containing compound in the two power active layers 130 and 130′ may be the same or different compounds.

FIG. 3 shows a schematic diagram of an electrode structure of a lithium ion battery according to a third embodiment of the present disclosure. Elements sharing the same labeling are the same elements. Details of the same elements can be referred from associated descriptions of the foregoing embodiments, and shall be omitted herein.

Referring to FIG. 3, the difference of the present embodiment from the embodiment as shown in FIG. 1 is in that, an electrode structure 400 of a lithium ion battery comprises two energy active layers 120 and 220 and two power active layers 130 and 230. The two power active layers 130 and 230 are respectively formed on a first surface 110a of the current collector 110 and a second surface 110b opposite the first surface 110a. The two energy active layers 120 and 220 are respectively formed on the first surface 110a and the second surface 110b of the current collector 110. The two power active layers 130 and 230 are respectively formed on the energy active layers 120 and 220 respectively corresponding to the first surface 110a and the second surface 110b of the current collector 110. That is, the power active layer 130 is formed on the energy active layer 120 corresponding to the first surface 110a of the current collector 110, and the power active layer 230 is formed on the energy active layer 220 corresponding to the second surface 110b of the current collector 110. In one embodiment, as shown in FIG. 3, the two energy active layers 120 and 220 are respectively located between the two power active layers 130 and 230 and the current collector 110. In an alternative embodiment, the two power active layers 130 and 230 may also be respectively located between the two energy active layers 120 and 220 and the current collector 110 (not shown).

Characteristics of the energy active layer 220, material types included in the energy active layer 220, and material types for forming the energy active layer 220 are the same as those of the energy active layer 120, and can be referred from foregoing descriptions associated with the energy active layer 120. Further, characteristics of the power active layer 230, material types included in the power active layer 230, and material types for forming the power active layer 230 are same as those of the power active layer 130, and can be referred from foregoing descriptions associated with the power active material layer 130. However, given that the lithium ion diffusion coefficients of the lithium-containing compounds in the power active layers 130 and 230 are greater than that of the lithium-containing compound in the energy active layers 120 and 220, the selections of the type of the lithium-containing compounds in the energy active layer 120, in the power active layer 130, in the energy active layer 220 and in the power active layer 230 may vary according to the conditions applied and are not limited thereto.

FIG. 4 shows a schematic diagram of an electrode structure of a lithium ion battery according to a fourth embodiment of the present disclosure. Referring to FIG. 4, the difference of the present embodiment from the embodiment as shown in FIG. 3 is in that, an electrode structure 500 of a lithium ion battery further comprises two power active layers 130′ and 230′ respectively formed on the first surface 110a and the second surface 110b of the current collector 110. In the embodiment, as shown in FIG. 4, the energy active layer 120 is formed between the two power active material layers 130 and 130′, and the energy active layer 220 is formed between the two power active layers 230 and 230′. Elements sharing the same labeling are the same elements. Details of the same elements can be referred from associated descriptions of the foregoing embodiments, and shall be omitted herein.

The embodiments of the present disclosure are further described below. In the following examples and comparison examples, electrode structures and materials are listed. However, it should be noted that the following examples are exemplifications rather than limitations to the disclosure.

1) Structural arrangement of embodiment 1 and 2: power active layer 130 (LiMn₂O₄)/energy active layer 120 (LiNi_0.4Mn_0.4Co_0.2O₂)/current collector 110.

2) Structural arrangement of comparison example 1: single-layered active layer (LiNi_0.4Mn_0.4Co_0.2O₂)/current collector.

3) Structural arrangement of comparison example 2: single-layered active layer (LiMn₂O₄) / current collector.

4) Structural arrangement of comparison example 3: single-layered active layer (LiMn₂O₄ and LiNi_0.4Mn_0.4Co_0.2O₂ mixed in the single layer)/current collector.

Referring to FIG. 1 and embodiments 1 and 2, which have a structural arrangement of power active layer 130 (LiMn₂O₄)/energy active layer 120 (LiNi_0.4Mn_0.4Co_0.2O₂)/current collector 110, the power active layer 130 may be formed of, 6 wt % Super P, 3 wt % PVDF (polyvinylidene fluoride, W1300) and 91 wt % LiMn₂O₄, and the energy active layer 1205may be formed of 5 wt % KS6, 2 wt % Super P, 4 wt % PVDF and 89 wt % LiNi_0.4Mn_0.4Co_0.2O₂, wherein the Super P and KS6 are conductive carbon black, and the W1300 and PVDF are used as an adhesive. That is, when the energy active layer 120 is formed on the current collector 110 and the power active layer 130 is formed on the energy active layer 120, a weight ratio of the first conductive particles (such as KS6 and Super P) to the energy active layer 120 may be 7 wt %, and a weight ratio of the second conductive particles (such as Super P) to the power active layer 130 may be 6 wt %. In other words, a weight ratio of the first conductive particles (such as KS6 and Super P) to the energy active layer 120 may be greater than a weight ratio of the second conductive particles (such as Super P) to the power active layer 130.

In Table 1, data of capacity retention of samples from the embodiments and the comparison examples are obtained under charge/discharge conditions of 10 (charged to 4.2 V)/10 (discharged to 2.75 V) for a charge/discharge cycle of 100 times.

	TABLE 1
	Thickness
	ratio (power		Capac-
	active layer		ity
	130:energy	C-rate capacity (mAh/g)	reten-
	active layer	0.5	3	4	tion
	120)	C[note 1]	C[note 1]	C[note 1]	(%)
Embodi-	5:5	124.7	100.0	60.0	91.1
ment 1
Embodi-	3:7	133.5	106.5	63.6	91.5
ment 2
Compar-	[note 2]	134.2[note 3]	111.8	46.4	90.1
ison
example 1
Compar-	[note 2]	102.3	83.7	49.2	91.2
ison
example 2
Compar-	[note 2]	120.0	98.5	46.2	82.6
ison
example 3
[note 1]0.5 C indicates that the current value can theoretically discharge for two hours, and 4 C indicates that the current value can theoretically discharge for 0.25 (¼) hour. That is to say, comparing 4 C and 0.5 C, 4 C is high-power discharge.
[note 2] Single-layered structure.
[note 3]The comparison example 1 utilizes high-energy active materials, and thus has a higher capacity under low C-rate discharge.

As observed from Table 1, under the condition of 40 discharge rate, the capacity of the comparison examples 1 to 3 is lower than the capacity of the embodiments 1 and 2. For example, under 40, the capacities of the embodiments are both above 60 mAh/g, whereas the capacitance capacities of the comparison examples are approximately at 46 to 49 mAh/g. That is, since the embodiments 1 and 2 have a two-layered structure formed of one power active layer and one energy active layer, the capacity of the embodiments 1 and 2 is greater than the capacity of the comparison example 1 having a single-layered active layer (LiNi_0.4Mn_0.4Co_0.2O₂), the comparison example 2 having a single-layered active layer (LiMn₂O₄) and the comparison example 3 having a single-layered active layer (LiMn₂O₄ and LiNi_0.4Mn_0.4Co_0.2O₂ mixed in the single layer).

Under a condition of a constant discharge current, for example, the discharge time of the embodiment 1 is about 0.25 hour, and the discharge time of the comparison example 1 is about 0.19 hour. Therefore, it is apparent that the electrode structure of the embodiments according to the embodiments of the present disclosure is capable of performing high-power discharge and has a longer high-power discharge period.

Further, it is also observed from Table 1 that, the capacity retention rate of the embodiments 1 and 2 are both above 90%. Thus, even after 100 times of charge/discharge, the electrode structures of the examples according to the embodiments of the present disclosure still maintain high capacity retention rates. In other words, the electrode structure of the embodiments is provided with a prolonged lifecycle even under a high-power discharge condition.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.

Claims

1. An electrode structure of a lithium ion battery, comprising: a current collector;at least one energy active layer, formed on the current collector, comprising a first lithium-containing compound and a plurality of first conductive particles; andat least one power active layer, formed on the energy active layer, comprising a second lithium-containing compound and a plurality of second conductive particles,wherein the first lithium-containing compound comprises lithium manganese cobalt nickel oxide (LiMnxCoyNizO2), where 0<x, y, z<1, and the second lithium-containing compound comprises lithium manganese oxide (Li M n2O4),wherein a weight ratio of the first conductive particles to the energy active layer is greater than a weight ratio of the second conductive particles to the power active layer,wherein the second lithium-containing compound has a lithium ion diffusion coefficient greater than a lithium ion diffusion coefficient of the first lithium-containing compound, andwherein the first lithium-containing compound has a specific capacity greater than a specific capacity of the second lithium-containing compound.

2. The electrode structure according to claim 1, wherein the specific capacity of the first lithium-containing compound is greater than or equal to 140 mAh/g.

3. The electrode structure according to claim 1, wherein the first conductive particles and the second conductive particles respectively comprise vapor grown carbon fiber (VGCF), conductive carbon black, graphite, a nano-sized carbon material, acetylene black, or the combinations thereof.

4. The electrode structure according to claim 1, wherein a weight ratio of the first conductive particles to the energy active layer is 0.5 to 20 wt %.

5. The electrode structure according to claim 1, wherein a weight ratio of the second conductive particles to the power active layer is 3 to 80 wt %.

6. The electrode structure according to claim 1, wherein the specific surface area of the first conductive particles is 10 to 100 m2/g.

7. The electrode structure according to claim 1, wherein the specific surface area of the first conductive particles in the energy active layer is greater than the specific surface area of the second conductive particles in the power active layer.

8. The electrode structure according to claim 1, wherein the thickness of the energy active layer is greater than the thickness of the power active layer.

9. The electrode structure according to claim 1, wherein the thickness of the energy active layer and the thickness of the power active layer are the same.

10. The electrode structure according to claim 1, wherein there are at least two power active layers and at least two energy active layers, the two energy active layers are respectively formed on a first surface of the current collector and a second surface opposite the first surface, and the two power active layers are respectively formed on the energy active layers respectively corresponding to the first surface and the second surface of the current collector.