WO2018176254A1

WO2018176254A1 - Electrode active material, an anode and a battery containing said electrode active material, and a method for preparing a battery

Info

Publication number: WO2018176254A1
Application number: PCT/CN2017/078550
Authority: WO
Inventors: Xiaogang HAO; Rongrong JIANG; Lei Wang
Original assignee: Robert Bosch Gmbh
Priority date: 2017-03-29
Filing date: 2017-03-29
Publication date: 2018-10-04
Also published as: CN110462890A; CN110462890B

Abstract

The present invention relates to an electrode active material for lithium ion batteries, which contains granular porous silicon or silicon alloy, and sodium ions, wherein the sodium ions are intercalated into the granular porous silicon or silicon alloy. The present invention also relates to an anode containing said electrode active material, and to a lithium-ion battery containing said anode. The present invention further relates to a method for preparing a lithium-ion battery.

Description

ELECTRODE ACTIVE MATERIAL, AN ANODE AND A BATTERY CONTAINING SAID ELECTRODE ACTIVE MATERIAL, AND A METHOD FOR PREPARING A BATTERY

Technical Field

Background Art

Silicon is a promising candidate anode material owing to its high theoretical specific capacity of 4200 mAh/g for Li_4.4Si. Nevertheless, two issues are considered to be critical to realize its application. One is the volume change during the charging and discharging processes, which causes cracking and crumbling of the electrode material, and consequently loss of electrical contact between individual silicon particles and a severe capacity drop. The other is the property of the surface layer on Si in contact with the electrolyte, also known as the solid-electrolyte-interface (SEI) .

Summary of Invention

The object of the present invention is solve the following problems: volume change during the charging and discharging processes, poor Li⁺ conductivity, and poor electronic conductivity.

Said object, according to one aspect, can be achieved by an electrode active material for lithium ion batteries, which contains granular porous silicon or silicon alloy, and sodium ions, wherein the sodium ions are intercalated into the granular porous silicon or silicon alloy.

According to another aspect of the present invention, an anode is provided, which contains the electrode active material according to the present invention.

According to another aspect of the present invention, a lithium-ion battery is provided, which contains the anode according to the present invention.

Said object, according to another aspect, can be achieved by a method for preparing a lithium-ion battery, said method including the following steps:

1) providing a cathode active material together with one or more sodium source materials, and providing granular porous silicon or silicon alloy as the anode active material；

2) assembling the cathode active material together with one or more sodium source materials of 1) , the anode active material of 1) , and electrolyte to obtain a lithium-ion battery；

3) subjecting the lithium-ion battery of 2) to a formation process.

Brief Description of Drawings

Each aspect of the present invention will be illustrated in more detail in conjunction with the accompanying drawings, wherein :

Figures 1 ～ 3 are schematic drawings of the formation process of the method according to the present invention；

Figure 4 shows the cycling performances of the lithium-ion batteries of Example 1 (E1) , Example 2 (E2) , Example 3 (E3) , and Comparative Example (CE) .

Detailed Description of Preferred Embodiments

All publications, patent applications, patents and other references mentioned herein, if not otherwise indicated, are explicitly incorporated by reference herein in their entirety for all purposes as if fully set forth.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.

When an amount, concentration, or other value or parameter is given as either a range, preferred range or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range.

The present invention, according to one aspect, relates to an electrode active material for lithium ion batteries, which contains granular porous silicon or silicon alloy, and sodium ions, wherein the sodium ions are intercalated into the granular porous silicon or silicon alloy.

In accordance with an embodiment of the electrode active material according to the present invention, the sodium ions can be present in a form of sodium-silicon alloy. As illustrated in Fig. 3, the sodium ions are not extracted from the anode material any more at the end of the formation process and during the subsequent cycling processes, but retained in the granular porous silicon or silicon alloy to form a sodium-silicon alloy. Since the radius of sodium ions is bigger than that of lithium ions, the sodium ions can act as pillars in the silicon structure during cycling, so as to diminish volume shrinking during cycling and keep the channels for lithiation/delithiation open. On the other hand, lithium ions can be extracted from and intercalated into the sodium source material, in addition to the cathode active material, during the subsequent cycling processes, wherein the sodium ions of the sodium source material have been partially replaced with lithium ions.

In accordance with another embodiment of the electrode active material according to the present invention, the content of the sodium ions can be 0.1 –5 wt. ％, preferably 0.5 –2 wt. ％, more preferably 0.8 –1.5 wt. ％, based on the weight of the electrode active material.

Since the radius of sodium ions is bigger than that of lithium ions, only a small amount of the sodium ions can be intercalated into the silicon structure.

In accordance with another embodiment of the electrode active material according to the present invention, the average diameter of the granular porous silicon or silicon alloy can be 20 nm –20 μm, preferably 0.1 –10 μm.

In accordance with another embodiment of the electrode active material according to the present invention, the BET specific surface area of the granular porous silicon or silicon alloy can be 5 –500 m²/g.

In accordance with another embodiment of the electrode active material according to the present invention, the pore volume of the granular porous silicon or silicon alloy can be 0.3 – 50.0 cm³/g.

In accordance with another embodiment of the electrode active material according to the present invention, the average pore diameter of the granular porous silicon or silicon alloy can be 0.2 nm –0.1 μm.

The present invention, according to another aspect, relates to an anode, which contains the electrode active material according to the present invention.

The present invention, according to a further aspect, relates to a lithium-ion battery, which contains the anode according to the present invention.

The present invention, according to another aspect, relates to a method for preparing a lithium-ion battery, said method including the following steps:

3) subjecting the lithium-ion battery of 2) to a formation process.

1) Providing a cathode active material together with one or more sodium source materials, and providing granular porous silicon or silicon alloy as the anode active material

In step 1) a cathode active material together with one or more sodium source materials can be provided, and granular porous silicon or silicon alloy can be provided as the anode active material.

In accordance with an embodiment of the method according to the present invention, the sodium source materials can be one or more selected from the cathode active materials usable in sodium ion batteries. Particularly the sodium source materials can be one or more selected from the group consisting of

- binary, ternary or quaternary oxides of sodium and one or more transition metals；

- sulphates of sodium and one or more transition metals；

- sodium ferrocyanide, and ferrocyanides of sodium and one or more transition metals；

- phosphates of sodium and one or more transition metals；

- sodium pyrophosphate, and pyrophosphates of sodium and one or more transition metals；

- sodium fluorophosphate, and fluorophosphates of sodium and one or more transition metals； and

- organic sodium salts,

wherein said one or more transition metals can be selected from the group consisting of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc.

In accordance with another embodiment of the method according to the present invention, the sodium source materials can be one or more selected from the group consisting of sodium vanadium phosphate, sodium iron phosphate, sodium vanadium fluorophosphate, sodium iron fluorophosphate, and sodium ferrocyanide.

In accordance with another embodiment of the method according to the present invention, the sodium source material can be dehydrated.

In accordance with another embodiment of the method according to the present invention, the weight proportion of the cathode active material to the sodium source material can be 12.6 : 1 –9 : 1, preferably 11.6 : 1 –10 : 1, more preferably 11.1: 1 –10.5 : 1.

2) Assembling the battery

In step 2) the cathode active material together with one or more sodium source materials of step 1) , the anode active material of step 1) , a separator, and an electrolyte such as 1M LiPF₆ in EC: DMC (1: 1 in molar ratio) can be assembled to obtain a lithium-ion battery.

In particular, the cathode active material together with one or more sodium source materials of step 1) can be mixed with carbon black, graphite and a binder such as poly- (vinyl difluoride) (PVDF) in a solvent such as DMF, TMF, THF, or NMP, and pasted onto an aluminium foil, and dried. On the other hand, the anode active material of step 1) can be mixed with carbon black, graphite and a binder such as sodium polyacrylate, and pasted onto a copper foil, and dried.

3) Formation process

In step 3) the lithium-ion battery of step 2) can be subjected to a formation process.

In accordance with another embodiment of the method according to the present invention, the formation process can be carried out at a current density of C/5 –C/100, preferably C/10 –C/50, more preferably about C/20.

In accordance with another embodiment of the method according to the present invention, during the formation process, the lithium-ion battery of step 2) can be charged to 3.7 –4.0 V, preferably 3.8 –3.9 V, more preferably about 3.85 V, held for 1 –10 hours, preferably 4 –6 hours, and then further charged to the charge cutoff voltage.

In accordance with another embodiment of the method according to the present invention, the formation process can be carried out to a charge cutoff voltage of 4.15 –4.25 V, preferably about 4.2 V, and to a discharge cutoff voltage of 2.4 –2.6 V, preferably about 2.5 V.

In accordance with another embodiment of the method according to the present invention, the formation process can be carried out to a charge cutoff voltage of 4.3 –4.4 V, preferably about 4.35 V, and to a discharge cutoff voltage of 2.9 –3.1 V, preferably about 3.0 V.

In accordance with another embodiment of the method according to the present invention, during the formation process, sodium ions can be extracted from the cathode into the electrolyte (see Fig. 1) , and intercalated from the electrolyte into the anode (see Fig. 2) .

In accordance with another embodiment of the method according to the present invention, during the formation process, sodium ions can be intercalated into the granular porous silicon or silicon alloy of the anode active material to form a sodium-silicon alloy. As illustrated in Fig. 3, the sodium ions are not extracted from the anode material any more at the end of the formation process and during the subsequent cycling processes, but retained in the granular porous silicon or silicon alloy to form a sodium-silicon alloy. Since the radius of sodium ions is bigger than that of lithium ions, the sodium ions can act as pillars in the silicon structure during cycling, so as to diminish volume shrinking during cycling and keep the channels for lithiation/delithiation open. On the other hand, lithium ions can be extracted from and intercalated into the sodium source material, in addition to the cathode active material, during the subsequent cycling processes, wherein the sodium ions of the sodium source material have been partially replaced with lithium ions.

4) Replace with fresh electrolyte

In accordance with another embodiment of the method according to the present invention, said method can optionally further include a step 4) after step 3) , in which step 4) the electrolyte can be replaced with fresh electrolyte having the same composition such as 1 M LiPF₆ in EC: DMC (1: 1 in molar ratio) , so that the electrolyte in the battery essentially does not contain sodium ions any more, as illustrated in Fig. 3.

According to the present invention, sodium can be used to activate the silicon anode. The sodium source materials can be initially incorporated into the cathode. During the first formation cycle, sodium ions can be extracted from the cathode structure, and diffuse from the cathode side to the anode side. And then, lithium and sodium ions in the electrolyte can be intercalated into the silicon anode.

Since the radius of sodium ions is bigger than that of lithium ions, the sodium ions can act as pillars in the silicon structure, so as to diminish the volume change during the charging and discharging processes. Thus, a better cycling performance and a better rate capability can be achieved.

In particular, the following problems can be solved by the present invention:

1) Volume change during the charging and discharging processes:

When some sodium ions are intercalated into the silicon structure, the volume of the silicon structure will expand, but not shrink, so that the volume change can be diminished；

2) Poor Li⁺ conductivity:

As some sodium ions are intercalated into the silicon structure, the diffusion channel for lithium ions can be expanded, so as to enhance the Li⁺ conductivity；

3) Poor electronic conductivity:

Continuous volume change results in loss of electrical contact between silicon particles, while according to the present invention, the volume change can be diminished, and a better electronic conductivity can be achieved.

Example 1 (E1) :

Preparing the cathode:

Na₄Fe (CN) ₆·xH₂O was used as the sodium source material, and dehydrated overnight to obtain Na₄Fe (CN) ₆. Then Na₄Fe (CN) ₆ was mixed with conductive carbon black Super P (commercially available from Timcal) in a weight ratio of 8 : 2 by a ball mill machine at a speed of 200 rpm for 2 hours to obtain a preliminary mixture.

10 g of the preliminary mixture, 86.5 g of NCM111 (commercially available from BASF) , 2 g of PVDF (commercially available from Solef) , 1 g of conductive carbon black Super P (commercially available from Timcal) and 0.5 g of flake graphite (commercially available from Timcal) were weighed, and then dry blended to obtain a intermediate mixture.

The intermediate mixture was added to NMP solvent to obtain a cathode slurry, wherein the solid content of the cathode slurry was adjusted to about 68 wt. ％. The cathode slurry was pasted onto an aluminium foil, and dried at about 80℃, so as to obtain the cathode.

Preparing the anode:

40 wt. ％of granular porous silicon alloy (commercially available from 3M) , 40 wt. ％of graphite (commercially available from BTR) , 10 wt. ％of sodium polyacrylate (NaPAA) , 8 wt.％of flake graphite (commercially available from Timcal) and 2 wt. ％of conductive carbon black Super P (commercially available from Timcal) were used to prepare an anode composition. The anode composition was pasted onto a copper foil, and dried, so as to obtain the anode.

Assembling the battery:

1 M LiPF₆ in dimethyl carbonate (DMC) and ethylene carbonate (EC) (1: 1 in molar ratio) was used as the electrolyte. PI film (commercially available from DuPont) was used as the separator.

The cathode, the anode, the electrolyte, and the separator were assembled in an argon-filled glove box (MB-10 compact, MBraun) to obtain a pouch cell.

Formation process and subsequent cycling processes:

The electrochemical performance was evaluated on a LAND-CT 2001A Battery test system (Wuhan, China) at room temperature.

The pouch cell was subjected to a formation process, in which the pouch cell was charged to 3.85 V at a current density of C/20, held for 5 hours, further charged to 4.2 V, and discharged to 2.5 V. During the subsequent cycling processes the pouch cell was charged to 4.2 V and discharged to 2.5 V at a current density of 0.5C.

Fig. 4 shows the cycling performances of the lithium-ion battery of Example 1 (E1) .

Example 2 (E2) :

Example 2 (E2) was carried out similar to Example 1, except that during the subsequent cycling processes the pouch cell was charged and discharged at a current density of 0.1C every 50 cycles and at a current density of 0.5C for other cycles.

Fig. 4 shows the cycling performances of the lithium-ion battery of Example 2 (E2) .

Example 3 (E3) :

Example 3 (E3) was carried out similar to Example 1, except that during the formation process the pouch cell was charged to 3.85 V at a current density of C/20, held for 5 hours, further charged to 4.35 V, and discharged to 3 V； and that during the subsequent cycling processes the pouch cell was charged to 4.35 V and discharged to 3 V at a current density of 0.1C every 50 cycles and at a current density of 0.5C for other cycles.

Fig. 4 shows the cycling performances of the lithium-ion battery of Example 3 (E3) .

Comparative Example (CE) :

Comparative Example (CE) was carried out similar to Example 1, except that the cathode was prepared without sodium source material.

Fig. 4 shows the cycling performances of the lithium-ion battery of Comparative Example (CE) .

Potential applications of the electrode active material according to the present invention include, but are not limited to, high-energy-density lithium ion batteries with acceptable high power density for energy storage applications, such as power tools, photovoltaic cells and electric vehicles.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. The attached claims and their equivalents are intended to cover all the modifications, substitutions and changes as would fall within the scope and spirit of the invention.

Claims

An electrode active material for lithium ion batteries, characterized in that the electrode active material contains granular porous silicon or silicon alloy, and sodium ions, wherein the sodium ions are intercalated into the granular porous silicon or silicon alloy.
The electrode active material of claim 1, characterized in that the sodium ions are present in a form of sodium-silicon alloy.
The electrode active material of claim 1 or 2, characterized in that the content of the sodium ions is 0.1 –5 wt. ％, preferably 0.5 –2 wt. ％, more preferably 0.8 –1.5 wt. ％, based on the weight of the electrode active material.
The electrode active material of any one of claims 1 to 3, characterized in that the granular porous silicon or silicon alloy has an average diameter of 20 nm –20 μm, preferably 0.1 –10 μm.
The electrode active material of any one of claims 1 to 4, characterized in that the granular porous silicon or silicon alloy has a BET specific surface area of 5 –500 m²/g.
The electrode active material of any one of claims 1 to 5, characterized in that the granular porous silicon or silicon alloy has a pore volume of 0.3 –50.0 cm³/g.
The electrode active material of any one of claims 1 to 6, characterized in that the granular porous silicon or silicon alloy has an average pore diameter of 0.2 nm –0.1 μm.
An anode for lithium ion batteries, characterized in that the anode contains the electrode active material of any one of claims 1 to 7.
A lithium-ion battery, characterized in that the lithium-ion battery contains the anode of claim 8.
A method for preparing a lithium-ion battery, said method including the following steps:

1) providing a cathode active material together with one or more sodium source materials, and providing granular porous silicon or silicon alloy as the anode active material；

2) assembling the cathode active material together with one or more sodium source materials of 1) , the anode active material of 1) , and electrolyte to obtain a lithium-ion battery；

3) subjecting the lithium-ion battery of 2) to a formation process.
The method of claim 10, characterized in that the sodium source materials are one or more selected from the cathode active materials usable in sodium ion batteries.
The method of claim 10 or 11, characterized in that the sodium source materials are one or more selected from the group consisting of

- binary, ternary or quaternary oxides of sodium and one or more transition metals；

- sulphates of sodium and one or more transition metals；

- sodium ferrocyanide, and ferrocyanides of sodium and one or more transition metals；

- phosphates of sodium and one or more transition metals；

- sodium pyrophosphate, and pyrophosphates of sodium and one or more transition metals；

- sodium fluorophosphate, and fluorophosphates of sodium and one or more transition metals； and

- organic sodium salts.
The method of claim 12, characterized in that said one or more transition metals are selected from the group consisting of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc.
The method of any one of claims 10 to 13, characterized in that the sodium source materials are one or more selected from the group consisting of sodium vanadium phosphate, sodium iron phosphate, sodium vanadium fluorophosphate, sodium iron fluorophosphate, and sodium ferrocyanide.
The method of any one of claims 10 to 14, characterized in that the sodium source material is dehydrated.
The method of any one of claims 10 to 15, characterized in that the weight proportion of the cathode active material to the sodium source material is 12.6 : 1 –9 : 1, preferably 11.6 : 1 –10 : 1, more preferably 11.1: 1 –10.5 : 1.
The method of any one of claims 10 to 16, characterized in that the formation process is carried out at a current density of C/5 –C/100, preferably C/10 –C/50, more preferably about C/20.
The method of any one of claims 10 to 16, characterized in that during the formation process, the lithium-ion battery of 2) is charged to 3.7 –4.0 V, preferably 3.8 –3.9 V, more preferably about 3.85 V, held for 1 –10 hours, preferably 4 –6 hours, and then further charged to the charge cutoff voltage.
The method of any one of claims 10 to 18, characterized in that the formation process is carried out to a charge cutoff voltage of 4.15 –4.25 V, preferably about 4.2 V, and to a discharge cutoff voltage of 2.4 –2.6 V, preferably about 2.5 V.
The method of any one of claims 10 to 19, characterized in that the formation process is carried out to a charge cutoff voltage of 4.3 –4.4 V, preferably about 4.35 V, and to a discharge cutoff voltage of 2.9 –3.1 V, preferably about 3.0 V.
The method of any one of claims 10 to 20, characterized in that during the formation process, sodium ions are extracted from the cathode into the electrolyte, and intercalated from the electrolyte into the anode.
The method of 21, characterized in that during the formation process, sodium ions are intercalated into the granular porous silicon or silicon alloy of the anode active material to form a sodium-silicon alloy.
The method of any one of claims 10 to 22, characterized in that after step 3) , the electrolyte is replaced with fresh electrolyte having the same composition.