Anode material for lithium batteries

Abstract

Primary and secondary Li-ion and lithium-metal based electrochemical cell The suppression of gas generation is achieved through the addition of an or additives to the electrolyte system of respective cell, or to the cell itself it be a liquid, a solid- or plastized polymer electrolyte system. The gas ion additives are primarily based on unsaturated hydrocarbons.

Description

BACKGROUND OF THE INVENTION

[0003] Rechargeable lithium battery technology has become an important source in providing new, lightweight and high energy density batteries for many applications growing with the electronic industry. These batteries have gained increased attention because of their possible utilization for high power applications such as hybrid electric vehicles. The LixC6/Li1−xCoO2 cell is widely commercialized, and is also the best known lithium ion battery cell chemistry in which L1−x-CoO2 plays the role of the cathode or positive electrode while LixC6 acts as the anode or negative electrode. Theoretically during the charge, lithium ions can be extracted from the layered structure of LiCoO2 and then inserted into the carbonaceous structure, leading to the formation of CoO2 and Li6C the hypothetical phases. At the top of the charge, highly lithiated carbon or graphite is a very reactive material, particularly in the case of cells made of cathodes containing nickel and flammable organic electrolytes. Therefore, there is a major concern to address the issue of the safety of the cells which leads to introducing Li4Ti5O12 as an alternative to carbon.

[0004] Li4Ti5O12 has a spinel structure and can be written as Li8a[Ti1.67Li0.33]16dO4. Lithium is inserted into the structure, and then the rock-salt phase [Li2]16c[Ti1.67Li0.33]16dO4 is generated. Hence, a two-phase reaction provides a constant voltage at 1.5V. versus lithium metal. A major disadvantage of a Li4Ti5O12 electrode is its insulating character because it has poor electronic and ionic conductivities, which seriously limit its utilization for high rates application as a preferred anode. As a solution, several attempts of doping this material with materials such as Mg2+, Al3+ have been reported in order to improve its electronic conductivity.

SUMMARY OF THE INVENTION

[0005] To address this issue, this invention presents for the first time MIILi2Ti6O14 (M=Sr, Ba and those of the strontium metal series) as a new generation of non carbonaceous anode material with an original type structure.

[0006] Only two materials have been reported in strontium lithium titanium oxide phases. SrTiO3, in which Li+ is partially substituted for Ti4+ (SrTi0.9Li0.1O3−x), is a selective catalyst for oxidative dehydrogenation of lower alkanes. Sr0.4Li0.6Ti2O4 has also been developed as a superconductor oxide. Recently, SrO—TiO2—LiBO2 has been studied in a ternary system to determine the concentration and temperature range of spontaneous crystallization of SrTiO3. By accident, an unknown phase was found which later was attributed to a new SrLi2Ti6O14 phase. The structure of SrLi2Ti6O14 is very attractive and presents a lot of cavities which could allow rapid lithium ion diffusion within the host. SrLi2Ti6O14 is therefore expected to be a very good ionic conductor, although it should be electronically an insulating material because all the titanium ions are tetravalent, during the first charge Ti4+ is reduced to Ti3+ which leads to a mixed-valent electronically conducting SrLi2+xTi6O14. For these reasons, this material is expected to be a very promising non carbonaceous anode materials for lithium ion battery applications that need high capabilities and enhanced safety.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a plot showing the X-ray pattern of SrLi2Ti6O14 made at 950° C.;

[0008] FIG. 2 shows the structure of SrLi2Ti6O14;

[0009] FIG. 3 is a plot showing the voltage profile of a Li/SrLi2Ti6O14 cell for the first 35 cycles;

[0010] FIG. 4 is a plot showing the area-specific impedance (ASI) as function as state of charge for a Li/SrLi2Ti6O14 cell and a Li4Ti5O12 cell;

[0011] FIG. 5 is a plot showing the delivered charge capacity (mAh/g) of a Li/SrLi2Ti6O14 cell;

[0012] FIG. 6 is a plot showing the delivered discharge capacity (mAh/g) of a Li/SrLi2Ti6O14 cell;

[0013] FIG. 7 is a plot showing the voltage profile of a Li(Ni1/3Co1/3Mn1/3)O2/SrLi2Ti6O14 cell;

[0014] FIG. 8 is a plot showing the delivered discharge capacity (mih/g) of a Li(Ni1/3Co1/3Mn1/3)O2/SrLi2Ti6O14 cell (C/5 rate.);

[0015] FIG. 9 is a plot showing the area-specific impedance (ASI) as a function as state of charge of a Li(Ni1/3Co1/3Mn1/3)O2/SrLi2Ti6O14 cell;

[0016] FIG. 10 is a plot showing the voltage profile of a LiNi0.5Mn1.5O4/SrLi2Ti6O14 cell; and

[0017] FIG. 11 is a plot showing the delivered discharge capacity (mAh/g) of a LiNi0.5Mn1.5O4/SrLi2Ti6O14 cell.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Compositions of matter, articles of manufacture and methods for manufacture are set forth herein for preparation of battery electrodes and a non-aqueous lithium ion battery.

[0019] To that end, MLi2Ti6O14 (M=Sr, Ba) ceramics have been prepared by solid state reaction, starting from a mixture of strontium carbonate SrCO3 or barium carbonate BaCO3, lithium carbonate Li2CO3 and titanium (IV) oxide TiO2 anatase. The mixture was heated at 5° C./min up to 800° C. to allow a complete decomposition of the carbonates with evolution of CO2. After grinding, the powder was sintered at 950° C. for 24 h. The resulting white polycrystalline powder was examined by X-ray diffraction to check purity of the obtained phase, as shown in FIG. 2.

[0020] The positive electrode was prepared by mixing MLi2Ti6O14 (M=Sr, Ba) with 10 wt. % carbon SP and 10 wt. % PVdF binder in NMP solvent. The resulting paste was spread on copper foil. The electrolyte was 1M LiPF6 in (1:1) ethylene carbonate (EC) and diethyl carbonate (DEC) solvents. The cells were assembled inside a helium-filled dry-box and were evaluated using coin-type cells (CR2032: 1.6 cm2). The charge/discharge measurements were carried out between 0.5 and 2V potential range under 0.2 mA/cm2 current density.

Description of Preferred SrLi2Ti6O14 Structure

[0021] SrLi2Ti6O14 belongs to the SrO—Li2O—TiO2 ternary system. The unit cell is orthorhombic (Space group: Cmca, Z=8L) with the following crystalline parameters: a=16.570, b=11.15 and c=11.458 Å. The structure of SrLi2Ti6O14 is built by edge and corner sharing [TiO6] octahedra which form layers parallel to (100) plane. The consecutive layers are linked by sharing common corners along the a axis. The details of this unique structure are shown in FIG. 1.

Titanium Environment

[0022] A titanium atom is located preferably at a six fold oxygenated site in four different crystallographic positions. Ti(1) and Ti(2) octahedra share common edges which form [AX4] chains running along c direction. The remaining Ti(3) and Ti(4) octahedra are bounded by a common edge forming [A2X7] group which shares common corners with similar group forming a layer along (100) plane. The parallel [AX4] chains containing Ti(1) and Ti(2) octahedra are situated between [A2X7] layers and are linked to each others by common corners.

Lithium Environment

[0023] The lithium atom is preferably located in a tetrahedral oxygenated site sharing two oxygen atoms with [Ti(1),Ti(2)] titanium chain and two others with [Ti(3),Ti(4)] titanium layer. As it can be seen in FIG. 1, lithium atoms are isolated from each others and occupy tunnels within [TiO6] framework along the c direction.

Strontium Environment

[0024] The strontium atoms are situated in between every three consecutive [TiO6] chains and layers. They are coordinated to eleven oxygen atoms which form polyhedrons of triply capped distorted cube (FIG. 2).

Electrochemical Data of SrLi2Ti6O14

[0025] FIG. 3 shows the voltage profile of a Li/SrLi2Ti6O14 cell. Four lithium ions are insertable into SrLi2Ti6O14 leading to SrLi6Ti6O14 according to the following general reaction:

4Li+SrLi2Ti6O14⇄SrLi6Ti6O14

[0026] According to this reaction, SrLi2Ti6O14 provides a total theoretical capacity of 175 mAh/g.

[0027] FIG. 4 shows the areas specific impedance (ASI) of the Li/SrLi2Ti6O14 cell. The ASI of this material is around 60 ΩQ.cm2 which is much lower than that of Li4Ti5O12, which is around 150 ΩQ.cm2. As a result, the SrLi2Ti6O14 should exhibit much better rate performance as well as sustainable cycling characteristics than Li4Ti5O12. For the subsequent cycles, the capacity is much more stable and reaches 140 mAh/g constantly up to 35 cycles under C/5 rate.

[0028] To establish the electrochemical behavior of SrLi2Ti6O14 anode material in reel cell chemistry, cells with two cathodes were chosen to be built: Li(Ni1/3Co1/3Mn1/3)O2 layered oxide and LiNi0.5Mn1.5O2 spinel material.

Electrochemical Data of Li(Ni1/3Co1/3Mn1/3)O2/SrLi2Ti6O14 Cell

[0029] Li(Ni1/3Co1/3Mn1/3)O2 belongs to the list of layered oxide materials having an α-NaFeO2 structure type. This cathode has certain specificities which make it a very promising cathode for many battery applications. The predominant oxidation states of Ni, Co and Mn in the compound are 2+, 3+ and 4+ respectively, which means that the capacity of 150 mAh/g delivered in the range 3-4.3V is mostly arising from the oxidation of Ni2+ to Ni3+, with a limited Ni4+ generation at that cutoff voltage. During the charge/discharge process, Mn4+ ions are intact, leading to the cohesion and the stability of the structure because of the strong covalency of Mn—O bonds. Furthermore, a LiNi2+/3+1/3Co3+1/3Mn4+1/3O2 configuration is very suitable for Li-ion batteries since there is no generation of highly oxidizing and unstable Ni4+ ions, which play a major role in the mechanism of failure of the battery.

[0030] FIG. 7 shows the voltage profile between a 2 and 4.1 V voltage range of a cell made of Li(Ni1/3Co1/3Mn1/3)O2 as a positive electrode and SrLi2Ti6O14 as a negative electrode. The cell delivers a specific discharge capacity of 150 mAh/g at a C/5 rate. This capacity is not affected during subsequent cycle as seen in FIG. 8.

[0031] FIG. 9 represents the area specific impedance (ASI) of a cell built with Li(Ni1/3Co1/3Mn1/3)O2/SrLi2Ti6O14. These very low ASI values meet the preferred requirement established for a high power application such as hybrid electric vehicle.

Electrochemical Data of LiNi0.5Mn1.5O4/SrLi2Ti6O14 Cell

[0032] LiMn2O4 is a well known spinel cathode which has been widely studied for high energy battery application. The practical 100 mAh/g of this cathode is achieved at 4.3 V cutoff voltage. However, LiMn2O4 base cell chemistry encounters many problems that affect the cycle and the calendar life of the battery, such as the manganese dissolution during the charge/discharge processes. LiNi0.5Mn1.5O4 oxide formulation is an exception among the spinel family designated for the battery technology. The electrochemical reaction occurs at high voltage as to give raise to a flat plateau at 4.7 V. At the top of the charge, the material is able to deliver up to 140 mAh/g.

[0033] To improve the electronic conductivity of SrLi2Ti6O14 and hence its electrochemical performances, many methods could be employed. For example, this could be accomplished by the partial reduction of Ti4+ cations to Ti3+ cations by various mechanisms, including the preparation under reduced atmospheres such as H2, H2/N2, CO2/CO and similar environments. The material could also be coated with one or combination of different conductive metals, such as Cu, Ag, Fe and Ti, metal oxides including aluminum oxide, iron oxide, cupper oxide, titanium oxide, vanadium oxide, nickel oxide, and silver oxide and/or carbonaceous compounds. Additionally, various combinations of the these methods could also be used.

[0034] FIG. 10 shows the voltage profile of a cell made of LiNi0.5Mn1.5O4 as a positive electrode and SrLi2Ti6O14 as a negative electrode. The cell delivers a specific discharge capacity of 120 mAh/g at C/5 rate. FIG. 11 shows the cycle stability of a cell fabricated with this chemistry.

[0035] It should be understood that the above description of the invention and the specific examples and embodiments therein, while indicating the preferred embodiments of the present invention, are given only by demonstration and not limitation. Many changes and modification within the scope of the present invention may therefore be made without the parting from the spirit of the invention, and the invention includes all such changes and modifications.

Claims

1. A negative electrode material for a non-aqueous lithium ion battery having the general formula M1−xAxLi2−yByTi6−zCzO14−tQt, wherein M is selected from the group consisting of Ba, Sr, Ca, Mg, Pb, Sn, and a divalent cation of electronegativity allowing reaction, 0<x<0.5; 0<y<0.5; 0<z<0.5; 0<t<0.5; and where A, B and C comprise at least one divalent, trivalent or tetravalent metal, and wherein Q is one or more suitable monovalent or divalent anions.

2. The negative electrode material of claim 1, wherein the M divalent cations are partially replaced by at least one divalent, trivalent or tetravalent metal cation to provide an electrode comprising M1−xAxLi2Ti6O14, wherein 0<x<0.5.

3. The negative electrode material of claim 1, wherein the Li monovalent cations are partially replaced by at least one divalent, trivalent or tetravalent metal cation to provide an electrode comprising MLi2−yByTi6O14, wherein 0<y<0.5.

4. The negative electrode material of claim 1, wherein the Ti cations are partially replaced by at least one divalent, trivalent or tetravalent metal cations to provide an electrode MLi2Ti6−zCzO14, wherein 0<z<0.5.

5. The negative electrode material of claim 1, wherein the M, Li, Ti cations are partially replaced by at least one divalent, trivalent or tetravalent metal cation respectively, to provide an electrode comprising M1−xAxLi2−yByTi6−zCzO14, wherein 0<x<0.5; 0<y<0.5; 0<z<0.5.

6. The negative electrode material of claim 1, wherein the O divalent anions are partially replaced by at least one monovalent or divalent anions to provide an electrode comprising M1Li2AyTi6O14−tQt, wherein 0<t<0.5.

7. A non-aqueous lithium ion battery comprising a positive electrode, an electrolyte and the negative electrode material of claim 1.

8. A non-aqueous lithium ion battery comprising a positive electrode, an electrolyte and the negative electrode material of claim 2.

9. A non-aqueous lithium ion battery comprising a positive electrode, an electrolyte and the negative electrode material of claim 3.

10. A non-aqueous lithium ion battery comprising a positive electrode, an electrolyte and the negative electrode material of claim 4.

11. A non-aqueous lithium ion battery comprising a positive electrode, an electrolyte and the negative electrode material of claim 5.

12. A non-aqueous lithium ion battery comprising a positive electrode, an electrolyte and the negative electrode material of claim 6.

13. The negative electrode of claim 1, wherein the negative electrode is coated with a material selected from the group consisting of all conductive materials, carbon, and combinations thereof.

14. A lithium insertion material for a non-aqueous lithium ion battery having the general formula M1−xAxLi2−yByTi6−zCzO14−tQt, wherein M is selected from the group consisting of Ba, Sr, Ca, Mg, Pb, Sn, and divalent cations, 0<x<0.5; 0<y<0.5; 0<z<0.5; 0<t<0.5, A, B and C are at least one divalent, trivalent or tetravalent metal, and wherein Q is at least one monovalent or divalent anion.

15. The lithium insertion material of claim 14, wherein the lithium insertion material is a cathode material for non-aqueous lithium ion batteries.

16. The lithium insertion material of claim 14, wherein the lithium insertion material is an anode material for non-aqueous lithium ion batteries.

17. The lithium insertion material of claim 14, wherein the lithium insertion material has a general formula M1−xAxLi2−yByTi6−zMnzO14−tQt wherein titanium is preferably replaced my Manganese, M is selected from the group consisting of Ba, Sr, Ca, Mg, Pb, Sn, and divalent cations, 0<x<1; 0<y<1; 0<z<6; 0<t<0.5, A and B are at least one divalent, trivalent or tetravalent metal, Q is at least one monovalent or divalent anion.

18. The lithium insertion material of claim 17, wherein titanium is replaced by manganese, and wherein the lithium insertion material is a cathode material for non-aqueous lithium ion batteries.

19. A non-aqueous lithium ion battery, comprising a positive electrode as described in claim 18, an electrolyte and a negative electrode.

20. The lithium insertion material of claim 14, wherein the lithium insertion material has the formula SrLi2Ti6O14.

21. The negative electrode material of claim 1, wherein Ti4+ cations are reduced to Ti3+ cations by preparing the negative electrode material under a reduced atmosphere.

22. A non-aqueous lithium ion battery, comprising a positive electrode, an electrolyte and the negative electrode material of claim 21.

23. The negative electrode material of claim 1, further comprising a coating of a material selected from the group consisting of a conductive metals, a metal oxide, a carbonaceous compound and combinations thereof.

24. A non-aqueous lithium ion battery, comprising a positive electrode, an electrolyte and the negative electrode of claim 23.